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Cropping Systems Effect on Soil Biological Health and Sustainability


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The influence on the chemical and physical soil composition, exerted from the applied cropping system, is dominated by the amount and kind of residual plant material. The cropping system, defined by the cropping sequence and type, as well as by plant residual management and natural and/or artificial fertilization, shapes the biological soil activities and environment for the soil micro-biotic habitat. Also climate and soil type exert an influence on the soil’s biological activity in a significant amount. The effects, exerted from the farming practice on the soil microbial biomass, accumulate in a slow way and are often measureable only in the late stage, when changes in the microbial biomass already negatively affect fertility and stability of the soil ecosystem. Measuring the classical soil nutrition parameters does not always reveal these changes, and suitable soil health indicators are not established as a common standard. Soil microbial biomass turns out to be a good indicator for changes in the soil composition and shows potential for an early soil health indicator.
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© Springer Nature Singapore Pte Ltd. 2019
D. P. Singh, R. Prabha (eds.), Microbial Interventions in Agriculture and
K. Saharan · U. Singh ()
College of Agriculture, Agriculture University, Jodhpur, Rajasthan, India
K. C. Kumawat
Department of Microbiology, Punjab Agricultural University, Ludhiana, Punjab, India
C. S. Praharaj
Division of Crop Production, ICAR-Indian Institute of Pulses Research,
Kanpur, Uttar Pradesh, India
Cropping Systems Effect onSoil
Biological Health andSustainability
KrishnaSaharan, UmmedSingh, K.C.Kumawat,
The inuence on the chemical and physical soil composition, exerted from the
applied cropping system, is dominated by the amount and kind of residual plant
material. The cropping system, dened by the cropping sequence and type, as
well as by plant residual management and natural and/or articial fertilization,
shapes the biological soil activities and environment for the soil micro-biotic
habitat. Also climate and soil type exert an inuence on the soil’s biological
activity in a signicant amount. The effects, exerted from the farming practice on
the soil microbial biomass, accumulate in a slow way and are often measureable
only in the late stage, when changes in the microbial biomass already negatively
affect fertility and stability of the soil ecosystem. Measuring the classical soil
nutrition parameters does not always reveal these changes, and suitable soil
health indicators are not established as a common standard. Soil microbial bio-
mass turns out to be a good indicator for changes in the soil composition and
shows potential for an early soil health indicator.
Cropping systems · Pulses · Soil biology · Soil health · Soil microbial biomass ·
Soil enzymatic activity
11.1 Introduction
Global agriculture is facing a changing scenario, an outcome from globalized
agriculture production and worldwide trading of the products. With the industrial-
ization of the food production, a trend to large-scale monoculture production sys-
tems has taken over the traditional crop rotation cultures, with their benets for the
soil health. Agriculture systems in many countries and regions are facing so-called
second- generation problems characterized by degradation of the soil composition
and texture, nutritional depletion (imbalance) of the soil, accumulation of herbi-
cides and pesticides in the soil, resurgence of plant diseases and pest, depletion of
groundwater, and increasing soil salinity (Fig.11.1). These problems are on the
short term alleviated by higher input of fertilizers, manpower (labor), and natural
resources (e.g., articial watering) which leads to decline in farm prots if the
higher cost cannot be forwarded to the consumers. Crop rotation, as employed since
long time ago in small-scale farming, shows a promising way to counteract these
problems, enhances environmental safety, withstands weather aberrations, dampens
price uctuations, and regulates income from farming by maintaining or enhancing
the soil health. Soil health can be seen as the overall soil capability to yield healthy
plants in a sustainable long-term view, with a constant input of labor and external
resources (e.g., fertilizer), and holds the key to sustainable food production in order
to feed the increasing human population. Healthy soil can be dened by the ability
to (a) provide physical support for the landscape itself (hills, mountains), vegeta-
tion, and external structures (e.g., buildings); (b) buffer natural rainfalls and lter/
maintain the quality and level of groundwater; (c) produce plants, supply them with
Fig. 11.1 Soil health inuencers and benets in the cropping system
K. Saharan et al .
sufcient water, and provide the habitat for soil organisms; (d) biochemically cycle
and to retain nutrients that are essential for the growth and development of plants,
such as nitrogen, phosphorus, potassium, or carbon; and (e) maintain the natural
biodiversity and buffer against toxic contamination. These attributes are often inu-
enced by agricultural management practices using excessive articial inputs and the
choice of the cropping system (Norris and Congreves 2018). In order to promote a
successful and sustainable plant growth, the soil has to provide benecial functions
to the plants, which include (i) provide mineral nutrients for plant roots in proper
form, within root-vicinity (space) and at the required time; (ii) supply water in the
right quantity and with appropriate potential energy, available for ideally continu-
ous uptake by plant roots; (iii) support the growth and spread of the macro- and
micro-fauna as earthworms (Lumbricidae) and plant growth-promoting soil organ-
isms as rhizobacteria and mycorrhiza fungi; (iv) facilitate sufcient root growth in
providing low physical resistance by connected pores, supplying oxygen and
removing carbon dioxide and toxic gases, and allowing sufcient rooting depth to
generate the physical support needed.
Soil organic matter content is inuencing most of these functions to a high
degree. A high level of this soil organic matter is typically associated with higher
soil aggregation and reduced erosion, improved nutrient cycling, as well as inltra-
tion and also water retention and mobility (Meng etal. 2012). Recent research focus
areas to elucidate the interactions and relationship between soil quality and the
organic matter in soil are mainly (i) chelating agents (organic compounds) control-
ling the availability and toxicity of micronutrients for plants and related microor-
ganisms, (ii) soluble or easy oxidable carbon as source of energy for microbial
biomass, and (iii) conversion process of organic matter and its chemical energy in
the nutrition chain (trophic levels) of the soil ecosystem which cycles nutrients and
carbon. The productivity of the soil is primarily depending on its biological health,
which includes the composition and amount of the microbial biomass with respect
to organic carbon, soil nitrogen, and enzymatic activities. Microbes are the active
agents for transforming organic matter and for recycling nutrients, affecting the
sustainability in a large amount.
Another highly important biotic component of the soil ecosystem are microar-
thropods. They are involved in organic material decomposition, thereby increasing
their availability to microorganisms and stimulating the overall nutrient turnover.
Lacking general standards and minimum data sets turns objective assessment of soil
health parameters into a challenge. Current available indicators for soil health
include chemical properties (organic carbon, potentially mineralizable nitrogen),
microbial biomass as well as soil enzymes, and respiration activities. As rhizo-
spheric micro-organisms are contributing largely to the soil health condition, they
shall be incorporated into any biological indicators for soil quality (Schloter etal.
2018). Recent studies have already emphasized the need to include soil organisms
as an important parameter for soil health in order to reect their importance in nutri-
ent cycling, soil aggregation, and soil structure development. Linking proposed soil
health indicators directly to soil functions is suggested by several authors; neverthe-
less, till to date there are no common standards or general guidelines of data
11 Cropping Systems Eect onSoil Biological Health andSustainability
interpretation and value metrics describing the relation between soil biology com-
position/activity and soil health. This chapter’s objective is to provide a summary of
the soil health inuencers and their indicators. Subsequently a brief description of
commonly applied cropping systems and their exerted effects on soil fertility and
productivity of succeeding crops is given.
11.2 Dominant Cropping Systems
The term “cropping system” describes the crops, the cropping sequences, and plant-
ing techniques used in a repeating sequence on a given agricultural area over a
period of years. It represents the planting pattern employed by a farm, the allocation
of farm resources, and deployment of available technology, determining their
makeup. It comprises all time and physically related aspects in managing an agri-
cultural production system. This includes also cropping a number of different crops
grown simultaneously or in short succession on the same eld. Using natural
resources in an efcient and sustainable manner while generating a high yield and
stable income for the farmer without negative side effects on the ecological soil
environment characterizes ideal cropping systems. Cropping systems are either a
result of improvements in agriculture technique, driven by changing market demand
or available resources, dened by landowners or government decisions or simply
environment- and climate-imposed facts as, e.g., nonproductive periods in winter
times. Cropping systems can be mainly separated into sequential cropping systems
with a planned and time-wise regular pattern of different crops, grown on a certain
agricultural area, one after the other (crop rotation) and into intercropping systems
where two or more different crops are grown together (at the same time) and in a
spatial recurring sequence on a dened area of land. This means that different plant
species are either grown simultaneously in short succession of each other or time-
wise overlapping. Growing different plant species in a time sequential manner is
referred to as crop rotation, and growing different plants simultaneously on a dened
area is called intercropping (Malezieux etal. 2009). Cereal crops, legumes, oil-
seeds, and forage/fodder crops are the most important plants, and planting systems
based on these crop types are worldwide dominating.
Climate change and resulting drought conditions are widely expected to exert
higher challenges on food production systems in the future. Cropping yield is inu-
enced by agronomic factors and several environmental parameters, with water avail-
ability and optimum temperature ranges among the most critical environment
parameters (Awika 2011). Daryanto et al. (2016) have reported that agricultural
yield correlates with both optimum environmental conditions (e.g., temperature,
water, aridity) and agronomic parameters (i.e., crop species, phenological cycle, soil
texture) at the same time. In this entry, we describe the major following cropping
systems and soil enzymes, which affect the biological health of soil.
K. Saharan et al .
11.2.1 Cereal Systems
The cereals comprise a wide range of cultivated members of the grass family (mono-
cotyledonous Poaceae, former Gramineae), often grown in an annual cycle. The
plants feature a single growing cycle (monocarpic or semelparous species) and are
having usually long, thin stalks with their fruits (grains) concentrated at the end.
Examples of important cereals, where the starchy grains are used for food, are
wheat, rye, maize, rice, oats, sorghum, millet, and barley. The terminus cereal is also
used for secondary products that are processed out of the starchy grains of cereal
plants like ours, breads, or pasta as further products. Cereals are a classical,
worldwide- grown staple food with a higher (nutritional) energy contribution than
any other type of crops. They are also a rich vitamin, mineral, and carbohydrate
source and provide important fats, oils, and protein in their natural form as a whole
grain (Sarwar etal. 2013).
Cereal cropping systems represent a vast range of agricultural production meth-
ods with the large-scale wheat and rice production areas worldwide, where both are
often a classical monoculture cultivation system (Awika 2011). The specialization
of large wheat farms in North America or the growing conditions in water-ooded
elds for rice are resulting in these monoculture systems, but for rice, there are also
crop rotation sequences, with, e.g., rice-legume employed. In contrast to legumes,
cereals do not accumulate atmospheric nitrogen in nodules and require therefore
articial nitrogen supply for plant growth. The impact on the soil health of large-
scale monoculture production areas is an ongoing discussion. Despite huge yield
increase from this kind of cropping system, the needed articial nutrients supply
and the applied pesticides are affecting the soil health in a negative amount, which
is not denied anymore. The dominance of cereals has a reported number of disad-
vantages for the farming systems: (a) depletion of soil nutrients over time, requiring
replenishment by articial sources of nitrogen and other nutrients; (b) declining
factor productivity; (c) over reliance on high quantity of soil nutrients; (d) declining
soil health; (e) in cereal cultures hard-to-control weed population development; (f)
disease carryover between cereals, such as the root-borne crown root disease
(Fusarium pseudograminearum) and the take-all disease (Gaeumannomyces grami-
nis var. tritici); and (g) cyclic and simultaneous tendencies of market price move-
ments of cereal crops and the resulting income dependency of the farmers (Brennan
etal. 2004).
11.2.2 Pulse Systems
The second important group of crops, after cereals, are pulses. They provide a sig-
nicant and balanced contribution for the nutrition of predominantly vegetarian
populations. Their ability to biologically x atmospheric nitrogen (BNF) and to
release parts of unused nitrate into the soil makes them a highly valuable contributor
to soil nutrition and soil health. They are also known to improve the soil microbial
environment generally and to exudate organic compounds with low molecular
11 Cropping Systems Eect onSoil Biological Health andSustainability
weight. These compounds serve as a nutritional substrate to soil microorganisms,
resulting in the build-up of soil microbe populations (Lupwayi and Soon 2016).
Having deeper-reaching and more abundant roots, they can reach and utilize higher
amounts of water, stored in areas below the top-soil surface region, and are therefore
more resistant to drought conditions, compared to shallow-rooted plants. The deep-
reaching tap root system of pulse crops, like pigeon peas, makes them very suitable
for intercropping with cereals and oilseeds, having shallow roots and which are
often rain-fed. The table below is showing the various cropping systems for pulses
used in India, depending on the regional cropping zone within the vast country
(Singh et al. 2009). As indicated in the table, a sequential cropping system is
employed in many regions with an alternating cereal-pulse sequence, especially in
combination with rice as one seasonal cereal. Other cropping systems with the sole
rice-wheat sequence, as found in the Indo-Gangetic plains, are under threat as a
long-term decline in soil organic carbon (SOC) is observed, leading to a reduction
of the overall productivity (Table11.1).
As indicated in the table, a sequential cropping system is employed in many
regions with an alternating cereal-pulse sequence, especially in combination with
rice as one seasonal cereal. Other cropping systems with the sole rice-wheat
sequence, as found in the Indo-Gangetic Plains, are threatened as soil organic car-
bon (SOC) decline is observed in the long term, leading to a reduction of the overall
11.2.3 Oilseed Systems
Oilseeds are hardy crops and are reported as a suitable choice under rainfed condi-
tions. They have potential for increasing overall return (protability) by raising the
cropping intensity with their stable return under harsh environment conditions. With
their wide ability to adapt to environmental stress conditions, they benet not only
in terms of price. New introduced high-yield varieties are replacing lower yielding
traditional crops because of higher returns gained by the better utilization of mois-
ture and rainfall. The popular soybean delivers satisfactory yields in many countries
when grown in the post-rainy season (rabi/summer). Sunower can adapt to a wide
range of soil types and is suitable for late planting in case of delayed or failed mon-
soon rain, or in case crops planted in the Kharif season have failed to grow. As a
summer crop under limited irrigation, sesame shows a great potential in the high-
lands of Deccan (e.g., Andhra Pradesh/Telangana region). Safower also shows
economic advantage over other popular crops like coriander, chickpea, or rainfed
wheat. Brennan et al. (2004) reported that intercropping of pulses with oilseeds
turns out to be a protable combination, as often the growth density of pulses can be
kept and oilseed crops are grown additionally. Intercropping of winter pulses as
chickpea and lentils with oilseeds is a common practice in rainfed areas of India.
Studies conducted under AICPIP (during 1982–2006) showed that mustard-lentil,
mustard-chickpea combinations in northern plains, chickpea-linseed in Central
K. Saharan et al .
Table 11.1 Important pulse-based cropping systems in different agro-climatic zones
zones States represented
(mm) Cropping systems
1 Western
Jammu and
Himachal Pradesh,
Uttar Pradesh
Rice-chickpea/lentil/eld pea, maize-
chickpea/ eld pea, ragi-chickpea/lentil/
eld pea, maize/urdbean/mung
bean-wheat, pigeon pea-wheat,
mungbean/urdbean-mustard, common
2 Eastern
Assam, West
Bengal, Manipur,
Arunachal Pradesh
Summer rice-urdbean/mungbean,
rice-lathyrus, maize-maize-urdbean,
maize-pigeon pea/horse gram, maize-
chickpea/lentil/eld pea, jute-urdbean-
3 Lower
West Bengal 1300–
Maize-chickpea/lentil/eld pea, rice-
chickpea/lentil/eld pea, rice-
4 Middle
Uttar Pradesh and
Maize-wheat-summer mungbean/
urdbean, rice-potato-summer mungbean/
urdbean, rice-chickpea/lentil
5 Upper
Uttar Pradesh 720–980 Rice-wheat/potato-summer mungbean,
maize-wheat/potato-summer mungbean,
pigeon pea-wheat, mungbean/urdbean-
wheat, sorghum (fodder)-chickpea
6 Trans
Punjab, Haryana 360–890 Maize-potato-summer mungbean/
urdbean, rice/maize-wheat-summer
mungbean/ urdbean, maize-early
potato-late potato-summer mungbean/
urdbean, rice- chickpea/lentil, maize-
chickpea/ lentil/eld pea
7 Eastern
Plateau and
Hills Region
Madhya Pradesh,
Odisha, West
Early rice-urdbean, rice-rice-cowpea,
jute-maize-cowpea, jute-urdbean
8 Central
Plateau and
Hill Region
Madhya Pradesh,
Rajasthan, Uttar
Sorghum (grain/fodder)-chickpea,
fallow- chickpea, sorghum+pigeon
pea-fallow, pearl millet+pigeon
pea-fallow, rice/maize- chickpea/lentil/
eld pea, moth bean/mungbean/
urdbean-wheat, pearl millet-chickpea
9 Western
Plateau and
Hill Region
Madhya Pradesh,
Urdbean-rabi sorghum, sorghum-potato-
mungbean, cotton+urdbean/mungbean-
fallow, sorghum-wheat-cowpea/
mungbean, cotton/sorghum-chickpea,
11 Cropping Systems Eect onSoil Biological Health andSustainability
Plateau, and chickpea-safower in the peninsular zone are the intercropping
arrangements yielding highest return for the mentioned regions (Ali 1992; Singh
and Rathi 2003).
11.2.4 Forage andFodder Systems
Forage and fodder crops are a simple but also signicant contributor in cropping
systems. They are a simple answer to a common problem created by modern culti-
vation and fallowing practices, the decline in soil fertility, soil organic matter, and
erosion. Forage is positively used on any type of land but particularly on marginal
soils. It provides numerous benets as improvement of soil quality, enhanced water
management, reduction in weed population, increase in soil fertility (with legumes
used), and subsequent yield and health increase for the following (cereal) crops.
It also provides a more intense and deeper carbon sequestering and contributes
therefore in reducing greenhouse gases. Forages can also aid to lower cost for nitro-
gen fertilizer and energy associated with applying nutrients (Singh et al. 2012).
Farmers are using forage for positive results particularly on marginal cropland but
are achieving them on any type of land.
Table 11.1 (continued)
zones States represented
(mm) Cropping systems
10 Southern
Plateau and
Hill Region
Andhra Pradesh,
Tamil Nadu,
Maize-sorghum+pigeon pea, sorghum-
chickpea, pearl millet-horse gram,
mungbean/urdbean-safower, rice-
mungbean/urdbean/cowpea, mungbean-
sorghum/safower, mungbean-pigeon
pea, rice+rice mungbean/urdbean/
11 East coast
Plains and
Hills Region
Odisha, Andhra
Pradesh, Tamil
Nadu, Puducherry
Rice-mungbean/urdbean, sorghum-
mungbean/urdbean, tapoic+mungbean/
urdbean, rice-rice mungbean/urdbean,
rice-maize/cowpea, maize-horse gram/
pigeon pea/chickpea
12 West Coast
Plains and
Hills Region
Tamil Nadu,
Kerala, Goa,
13 Gujarat
Plains and
Hills Region
Gujarat 340–
Urdbean-safower/niger, cowpea-
safower, mungbean-tobacco, pearl
millet/sorghum+ pigeon pea-chickpea
14 Western Dry
Rajasthan 400 Pearl millet/ sorghum-
chickpea+mustard, moth bean/
mungbean-wheat, Cotton-chickpea
Adapted from Singh etal. (2009)
K. Saharan et al .
The numerous benets in both situations include higher soil fertility with legu-
minous crops, increased soil quality, improved water ltration and internal drain-
age, fewer disease in following cereal crops, reduced weed populations, higher
yield and better economics in subsequent crops, and intensied and deeper carbon
sequestering for greenhouse gas reduction. Research ndings reported that the sys-
tem of fodder production can vary regionally as well as locally or even from one
farmer to the next (Singh et al. 2012). The individual fodder production system
depends on available inputs as irrigation and fertilizers and also on insecticides/
pesticides as well as on the landscape (topography) and is typically optimized for
maximum livestock output per available production area. Maximum yield per pro-
duction site, measured in either digestible nutrients or maximum livestock products,
characterizes an ideal fodder system. Production shall also ensure sufcient succu-
lent, palatable, and nutritive fodder to feed livestock on a daily basis throughout the
year, and it shall be from high quality in terms of nutritional and avor parameters.
Growing high-yielding fodder crops, either as single or crop mixture, can increase
overall yield. Also growing several (three or four) fodder crops in succession is
helping to enhance production output on the given area. Even though forage requires
specialized harvesting machinery, it needs less input in nancial capital (cash).
Compared to earlier times, harvesting equipment can be shared more easily with
other farmers or rented from specialized organizations when needed. Some impor-
tant fodder crops, crop rotating schemes, and expected yield under different regions
in India are summarized in Table11.2.
11.3 Soil Biological Health Indicators
11.3.1 Soil Microbial Biomass
The microbial biomass in the soil is considered as the living fraction/anchor of the
soil organic matter (SOM), including bacteria, actinomycetes, fungi, algae, and
microfauna in general, and represents typically 3–5% of the organic carbon within
Table 11.2 Different cropping sequences for fodder crop production
No. Different cropping sequences Expected yield
1 Maize+cowpea–maize+cowpea+seem+mustard (300q/ha)(450q/
2 Sweet sudan+cowpea–berseem+oats (1000q/ha)(1000q/ha)
3 Hybrid Napier+Lucerne (1250q/ha)(850q/ha)
4 Maize+cowpea–jowar+cowpea–berseem+mustard (300q/ha)(400q/
5 Teosinte+bajra+cowpea–berseem+oats (1000q/ha)(1000q/ha)
6Sweet sudan+cowpeamustardoats+peas (1000q/ha)(250q/
7Jowarturnipsoats (1800q/ha)
Adapted from Geoffrey and James (2006)
11 Cropping Systems Eect onSoil Biological Health andSustainability
the soil. It also serves as reservoir for the nutrients, even though, generally, the pro-
portion of the biomass represents only 2–3% of the organic carbon (C) in soil. It is
reported that declines in crop diversity tend to reduce soil microbial biomass, alter
microbial functions, and threaten the provision of soil ecosystem services (McDaniel
and Grandy 2016). Soil organic matter, created by decay of plant material and act-
ing as an important source of plant nutrients, forms the variable (or labile) pool of
the soil microbial biomass (SMB) and is perceived as one of the highly important
contribution factors to soil fertility (Singh etal. 1989; Rai etal. 2018). Changes in
microbial biomass affect the cycling of soil organic matter, stability, and fertility of
the ecosystem in a negative way. Studies on soil microbial biomass carbon (SMBC),
nitrogen (SMBN), and phosphorus (SMBP) in different natural and disturbed eco-
systems showed an important inuence on labile pool of carbon (C) and mineral
nutrients (Smith and Paul 1990; Wardle 1992, 1999; Christos et al. 2014). The
microbial biomass is an important factor in the transformation of soil nutrients and
determines largely the biogeochemical cycle rate of C, N, and other nutrients. The
applied cropping system affects the soil microbial biomass. It has been reported that
crop rotations show to have large positive inuence on soil carbon, nitrogen micro-
bial biomass (McDaniel etal. 2014), plant pathogen suppression (Krupinsky etal.
2002), and yields (Smith etal. 2008; Riedell etal. 2009). This positive inuence on
the crop production has been generally referred to as the “rotation effect.” Any
change in the microbial biomass composition may inuence the fertility and organic
matter recycling in the soil and therewith the stability of that ecosystem. Many stud-
ies indicate a raise in soil microbial biomass with the addition of pulses in the crop-
ping system. Including mungbean in a rice-wheat sequence shows increase of
SMB.Similar results are found in the maize-based cropping systems, with maize-
wheat- mungbean returning higher soil microbial biomass carbon (SMBC) as com-
pared to maize-wheat only cropping (Singh et al. 2009). The effect of various
cropping systems and their inuence on the soil microbial biomass carbon and
nitrogen are compared in Table11.3. The type of vegetation, availability of sub-
strate, and other abiotic factors in an ecosystem are inuencing the microbial activ-
ity. Increased microbial activity has effect on the mineralization and reduction of
mobilization of important plant nutrients as N, P, and S.As a biological indicator or
index for soil, microbial activity can serve the dehydrogenase enzyme activity,
which shows positive correlation to pulse cropping. As a dynamic and living organ-
ism, the SMB and its activity determine the organic matter transformation and regu-
lation of the associated nutrient and energy cycling in soil. A turnover time of less
than once per year and a quick response to conditions which leads eventually to an
alteration of the soil quality turn the soil microbial biomass into a good pre- indicator
for changes in soil health. Seasonal uctuations induced from changes in climate
conditions also affect microbial biomass, which tends to positive correlation
(increase) with annual precipitation and shows negative correlation (decrease) with
higher annual temperatures. Crop residues and root biomass as well as nutrient
amendments, clay content, soil water content, and temperature inuence the SMB,
but also soil pH, C, N, and concentration of pesticides and heavy metals are affect-
ing the quantity and quality of the soil microbial biomass. Measuring the SMB is
K. Saharan et al .
Table 11.3 Soil microbial biomass carbon (SMBC), SMBN, SMBP, and SMBK parameters by various cropping systems
Cropping system Tillage practices
SMB (mg/kg soil)
ReferencesC N P K
Maize-wheat BF+FYM 298 Singh etal.
Maize-wheat-mungbean BF+FYM 350
Maize-wheat-maize-chickpea BF+FYM 338
Pigeonpea-wheat BF+FYM 305
Rice-wheat 305
Rice-wheat-mungbean 376
Rice-chickpea-rice-wheat 342
Rice-chickpea 336
Maize+wheat 132 Venkatesh etal.
Maize+wheat+maize+chickpea 135
Maize+wheat+mungbean 142
Pigeonpea+wheat 150
Rice-wheat CT -R 646 201 144 Choudhary
etal. (2018)
+Ri 1113 343 176
ZT -R 890 239 153
+Rm 1181 364 163
Maize-Wheat CT -R 895 244 157
+Ri 1500 590 208
ZT -R 1278 416 188
+Rm 1990 729 213
Chickpea Sole Rhizosphere 180 16 Tang etal.
Chickpea Sole Bulk soil 150 14
Chickpea+durum wheat Intercropped Rhizosphere 380 35
11 Cropping Systems Eect onSoil Biological Health andSustainability
Table 11.3 (continued)
Cropping system Tillage practices
SMB (mg/kg soil)
ReferencesC N P K
Durum wheat+chickpea Intercropped Rhizosphere 170 11
Chickpea+durum wheat Intercrop Bulk soil 250 20
Durum wheat Sole Rhizosphere 230 18
Durum wheat Sole Bulk soil 190 23
Durum wheat+lentil Intercropped Rhizosphere 275 13
Lentil+durum wheat Intercropped Rhizosphere 170 36
Lentil+durum wheat Intercrop Bulk soil 430 28
Lentil Sole Rhizosphere 155 24
Lentil Sole Bulk soil 160 20
Maize-Weat-Mungbean WS 448.4 Parihar etal.
Maize-Chickpea-Sesbania WS 470.0
Maize-Mustard-Mungbean WS 344.4
Maize-Maize-Sesbania WS 373.2
Rice+Wheat Field A MC 119 21.9 27.0 Yamashita etal.
Rice+Wheat MCC 88.7 18.6 17.0
Rice+Wheat CF 63.8 8.78 7.0
Rice+Wheat NF 47.8 3.55 8.5
Rice+Wheat Field B RSC 119 19.5 18.5
Rice+Wheat NPK 52.7 7.61 4.8
Rice+Wheat NP 42.8 3.71 5.0
aMC livestock manure compost plot, MCCF livestock manure compost plus chemical fertilizer plot, CF chemical fertilizer plot without application of livestock
Manure compost, NF no fertilizer plot, RSC rice straw compost plus chemical fertilizer plot, NPK chemical fertilizer plot, NP no potassium fertilizer plot, Field
A long-term application of livestock manure compost, Field B rice straw compost and chemical fertilizers, £ WS winter soil, MWMb maize-wheat-mung bean,
MCS maize chickpea-sesbania, MMuMb maize-mustard-mung bean, MMS maize-maize-sesbania, ΨCT conventional till, ZT zero till, R residue, i incorporated,
m mulched
K. Saharan et al .
therefore considered to be the most general and practical indicator, and an increase
is generally seen as a desired and benecial change of the soil health (Shukla etal.
2006). Soil Microbial Biomass Carbon
A small portion of the biologically signicant soil labile C comes from the
SMBC.As a fertility and soil health indicator, it is a sensitive parameter for soil
management practices and serves as reservoir of nutrients (as N, P, S), and content
in soil correlates in a positive way with the available soil organic matter. It has been
demonstrated that straw incorporation over 18years increased the biomass by about
50%, while changes in total organic matter remained undetected (Powlson et al.
1987). Chander and Brookes (1991) showed that the ratio of SMBC to soil organic-
C was a sensitive indication for heavy metal effects on the microbial biomass using
soils from two different eld experiments. Under tropical conditions, continuous
applications of fertilizers and organic manures have shown an increase in soil
microbial biomass-C and biomass-N with a balanced fertilization. The studies by
Wang etal. (2011) on SMBC and SMBN content from mixed plant residues revealed
that incorporating residues from more than two plant species into soils could
increase both SMBC and SMBN which then can contribute to restore vegetation
and soil fertility in the Loess Plateau. The sensitiveness of the soil microbial bio-
mass to changes in soil management qualies it as a good indicator for soil quality.
Tropical conditions accelerate the decomposition of plant materials and enhance the
transformation of SMB to SMBC.Supplemental applications of organic fertilizers
further increase the creation of SMBC in comparison to sole application of inor-
ganic fertilizers. For example, the applications of farmyard manure along with
N-P-K fertilizer result in higher SMBC concentrations as compared to fertilization
with N-P-K only. Soil Microbial Biomass Nitrogen
Part of the nitrogen potentially available for mineralization and available for plants
is out of the soil microbial biomass (Choudhary etal. 2018). This SMBN represents
a signicant sink or source for nitrogen to the plants. A substantial amount of soil-
borne N originates from pulses after their harvesting. Their unique ability xing
atmospheric N2 makes them a valuable SMBN donor, with a contribution to the soil
N budget in the range of 4–20kg/ha and with chickpea in the upper range of the
contribution. Soil Microbial Biomass Phosphorus
Phosphatic fertilizer continues to be a signicant player in intensive agriculture,
even though declining availability of phosphorus (P) and raising production cost
from depletion of natural resources turn it into a future critical issue. Legume crops
are a valuable source for soil N, but they also aid in the efcient utilization of native
P.The secretions of certain organic acid (root exudates) facilitate the solubilization
of various phosphorus forms and increase the available P as a result of P-acquisition
from insoluble phosphates through roots. This capacity makes legumes efcient in
11 Cropping Systems Eect onSoil Biological Health andSustainability
native utilization of P present in different forms. As an example, the ability of chick-
pea to access P, normally unavailable to other crops, in mobilizing hardly soluble
Ca-P by rhizosphere acidication through its citric acid root exudates in Vertisols,
whereas pigeon pea is known having the ability to dissolute Fe-P in Alsol. Soil Microbial Biomass Potassium
Potassium (K) in microbial cells inhabiting the soil is considered to be the major K
pool for plant growth. The high potassium demand of plants for their proper growth
turns it into one of the essential nutrients, with K uptake equivalent or greater than
the nitrogen uptake by the crops (Yamashita etal. 2014, Owa 2006). K is available
in four different forms in soil: water-soluble, exchangeable, non-exchangeable or
xed, and structural or mineral form. Most readily available for plants are the water-
soluble and exchangeable forms (Sparks 2011). The concentration of K is generally
regulated higher within inside the cells than in the outside environment (Uozumi
2011). Also bacteria and fungi accumulate K inside their cells to a concentration
above 0.18–0.2M (Slayman and Tatum 1964). This turns the soil microbial biomass
into a rich K pool. Despite this, relatively less is known in dealing with this potential
K source.
11.3.2 Soil Enzymatic Activities
Microbiota, a particular form of soil microorganisms, have an essential role in ele-
ments cycling and soil structure stabilization (Saha etal. 2008). They are also taking
the dual role as a source and sink for carbon and labile nutrients. Enzyme activities
are linked to the decomposition of organic matter and soil remediation processes
and to indicators of biochemical activities. In combination with other chemical or
physical parameters, they can determine the quality level of soil (Gelsomino etal.
2006), and enzyme activity estimates are often used as indicators for soil fertility
and microbial activity (Skujins 1978). Soil enzymes are reported to be important in
soil functions (Dick 1997; Alkorta etal. 2013), and their activity may serve as useful
indicators for changes in soil biology and biochemistry due to external management
and environmental factors (Dick 1994) as enzymes react on changes in soil manage-
ment long before changes in any other soil quality parameter becomes detectable.
Soil enzyme activities catalyze the principal biochemical reactions involved in
nutrient cycling and are highly responsive to natural and anthropogenic-induced
changes. They also serve a relevant role in organic matter decomposition and the
cycling of plant nutrients.
Soil enzyme activity can be considered as the accumulated long-term effect of
soil microbial activity and viable population at the sampling site. As a large amount
of samples can be analyzed in a short time (within few days) requiring only a small
amount of soil, they are suggested as sensitive indicators for soil fertility (Nannipieri
etal. 2012; Doran and Parkin 1994). The major soil enzymes and their related
functions are given in Table11.4 (Srinivasa etal. 2011; Das and Varma 2011). The
main groups of enzymes involved in nutrient cycles including dehydrogenases,
K. Saharan et al .
Table 11.4 The effect of different eld practices/ecosystem on various soil enzymes activities
Field practice C-cycling enzymes
enzymes Phosphatase
sulfatase Dehydrogenase Urease References
Horticulture land use
High High High Bhavya etal.
Continuous cropping
First increase then
decline (invertase)
High Low Sun etal.
Continuous cropping
First increase then
decline (invertase)
High Low Sun etal.
Conventional tillage
vs. no tillage
High High Choudhary
etal. (2018)
Degraded vs. native
Low (cellulose) Low Araújo etal.
Forest vs. pasture vs.
(β-glucosidase) in
forest, lowest in
agricultural soil
Highest (urease)
in pasture, lowest
in agricultural
Highest (alkaline
phosphatase) in
forest, lowest in
agricultural soil
and Dengiz
Organic residue with
RDF (maize residue in
rice and wheat
High (invertase) High protease High alkaline
High High Tao etal.
Organic vs.
unamended (in bell
High (β-glucosidase) High acid
High High Gopinath
etal. (2009)
fertilization, no
High High High High Nonsignicant Saha etal.
11 Cropping Systems Eect onSoil Biological Health andSustainability
Table 11.4 (continued)
Field practice C-cycling enzymes
enzymes Phosphatase
sulfatase Dehydrogenase Urease References
Conservational vs.
conventional tillage
High (β-glucosidase) High protease High High High Roldan etal.
Conventional tillage
vs. no tillage
High (cellulose)
under no tillage
High under no
under no
Balota etal.
Continuous cropping
First increase then
decline (invertase)
High Low Sun etal.
K. Saharan et al .
glucosidases, ureases, amidases, phosphatases, arylsulfatase, cellulases, and phenol
oxidases are described (Fig.11.2). Carbon Cycling Enzymes
The carbon cycle process denotes the main constituent process of all living
organisms, where primary producers x atmospheric carbon dioxide and transform
it to organic material. Microbes play a further important role in this cycle where
autotrophic microbes are capable to x carbon dioxide within the soil. Plants, as
primary organic material producers in our terrestrial ecosystems contribute in
signicant amount to carbon xation, although surface-dwelling algae and cyano-
bacteria, both free-living and symbiotic as lichens, may add to carbon xation in
some ecosystems in signicant amount (Gougoulias etal. 2014). The organic mate-
rial originating from the primary production is incorporated in living organisms and
forms part of the nonliving organic materials, derived from decaying life. The ulti-
mate recyclers of decaying organic material are heterotrophic bacteria and fungi.
This kind of saprotrophic microorganisms closes the carbon cycle by converting the
organic material, formed by the primary producers, back to carbon dioxide during
respiration. This process of organic matter decomposition utilizes the degradation
of nonliving organic material to derive energy for growth. Higher life forms, as
Fig. 11.2 Major soil enzymes as biological indicator of soil health
11 Cropping Systems Eect onSoil Biological Health andSustainability
herbivore and carnivore beings, digest with gastrointestinal tract-inhabiting
microbes organic material and support in this way the carbon dioxide cycle.
The mineralization of organic compounds occurs when they are entirely degraded
to inorganic components, like carbon dioxide, ammonia, and water. The main activ-
ists for organic matter decomposition in soil ecosystems are fungi, representing the
majority of the soil biomass. Nevertheless, bacteria as well as fungi are able to
decompose and degrade complex organic molecules that cannot be broken up by
higher organisms. A range of bacteria, especially out of Actinobacteria and
Proteobacteria, are able to degrade soluble organic molecules such as organic acids,
amino acids, and sugars (Eilers et al. 2010). Likewise, bacteria from phylum
Bacteroidetes can aid in degrading more recalcitrant carbon compounds like cellu-
lose, chitin, or lignin. Recalcitrant carbon compound-targeting bacteria may require
quite large amounts of available N for supporting the creation of extracellular and
transportation enzymes (Treseder etal. 2011), contrary to bacteria suited for low N
environments, which are more procient in metabolizing organic N compounds,
such as amino acids. In soils with abundance of Proteobacteria and Bacteroidetes,
a positive correlation of the net carbon mineralization rate was found, whereas it
correlated negatively with Acidobacteria (Craine etal. 2013). Nitrogen Cycling Enzymes
Nitrogen (N) is an essential element for protein and nucleic acids and is required by
all organisms. Organic sources deliver the needed nitrogen for animals, whereas
plants need nitrogen in inorganic forms, like ammonium and nitrate, or relatively
depolymerized N sources such as single amino acids (e.g., glycine) (Schimel and
Bennett 2004). Most microbes can utilize ammonium or nitrate for their growth, and
they also take an important role in the nitrogen cycle. These microbes execute sev-
eral processes not carried out by other organisms, like nitrogen xation, dissimila-
tory nitrate reduction to ammonia (DNRA), ammonication, nitrication, and
denitrication. The conversion rates of these microbial processes determine the
availability of nitrogen where low rates can result in limiting the productivity of the
underlying ecosystem. Only few microbial groups (e.g., nitrogen xation or nitri-
cation) mediate some of the process steps in the nitrogen cycle. These steps are
known as narrow processes, whereas other steps are mediated by many groups (e.g.,
DRNA) and are considered as broad processes. Ammonication is known as the
release of ammonium from soil organic matter during decomposition (Prosser
1989). Bacteria and archaea only carry out the biological reduction of atmospheric
nitrogen to ammonium (biological nitrogen xation– BNF). This BNF process is of
crucial importance for the functioning of the entire ecosystem as it is the sole natu-
ral process through which atmospheric N enters the biosphere (Aislabie and
Deslippe 2013). N-xation is catalyzed by the enzyme nitrogenase, an extremely
oxygen-sensitive enzyme, requiring an environment with low oxygen content for
activity. The N-xation is a process of high-energy expense; xing 1 Mol of N2
consumes the amount of 16 Mol of ATP.The produced ammonium becomes assimi-
lated into amino acids and subsequently polymerized into proteins. Nitrogen-
limiting conditions create an advantage for N-xing microbes. Plant exudates may
K. Saharan et al .
supply some of the energy required for N-xation which is carried out by free-living
microbes (e.g., Azotobacter, Burkholderia, Clostridium, and some methanogens),
some of them associated with the rhizosphere of plants, and by bacteria which form
symbiotic relationships with plants (e.g., Rhizobium, Mesorhizobium, and Frankia).
Rhizobia-forming root nodules in symbiotic relationships with human-introduced
legumes such as clover, lucerne, or lotus became a signicant nitrogen source for
New Zealand’s agricultural soils. In a similar way are native legumes (e.g., Sophora
and Clianthus) forming symbiotic relationships with Mesorhizobium or Rhizobium
leguminosarum (Weir etal. 2004). As reported, the nitrogen xation rate generated
by symbiotic rhizobia is often higher by a magnitude of two or three orders com-
pared to free-living soil bacteria, indicating a mutual benet for symbiotic life
forms. Phosphate Activity
The abundant organic phosphorus (P) in soil is able to provide nutrient P for plants
and soil-borne microbes after hydrolysis and the release of free phosphates into the
soil environment (Utobo and Tewari 2014; Condron etal. 2005). Plants and microbes
secrete phosphatase enzymes into the soil, which are catalyzing this process. This
secretion is actively driven by the demand for nutrient P or results from decaying
cell, as a passive form of release. While microorganisms belonging to genera
Actinomycetes produce rather negligible quantities of phosphatases are fungi, espe-
cially genera belonging to the Aspergillus and Penicillium type, as well as Bacillus
and Pseudomonas bacteria mostly neutral phosphatase producer, as reported by
Tarafdar and Chhonkar (1979). Phosphomonoesterase soil enzymes are showing
activity under alkaline as well as under acid conditions and are therefore among the
most studied enzymes. They can serve as biological soil quality indicators as they
are acting on P-compounds with low molecular structure, including polyphosphates,
sugar phosphates, and nucleotides (Makoi and Ndakidemi 2008). The evaluation of
phosphatase activity in grassland in the temperate climate zone revealed a strong
correlation between soil properties (P, N, pH, and clay content) and enzyme activity,
as reported by Turner and Haygarth (2005). The amount of plant roots-exuded acid
phosphatase differs between plant species, with legumes showing higher secretion
as compared to cereals (Ndakidemi 2006; Yadav and Tarafdar 2001; Li etal. 2004).
The higher P requirement of legume crops for the nitrogen xation process in sym-
biosis with bacteria may attribute to this observation (Joachim and Patrick 2008).
Crop management practice is also an active inuencer of the phosphatase process,
as the capability of soil mineral solubilization by phosphomonoesterases is consid-
ered to be on a higher level in the soil system with higher organic C content. Several
studies conrmed a positive correlation between soil organic matter content and
alkaline or acid phosphatase activity (Aon and Colaneri 2001; Aon etal. 2001), even
though only few studies are available investigating the inuence of crop manage-
ment options on phosphatase activity in the soil ecosystem (Joachim and Patrick
2008). Understanding the phosphatase activity dynamics in the soil ecosystem is an
important asset for anticipating the interactions as plant nutrient uptake and, in
consequence, plant growth are governed by these interactions (Das and Varma 2011).
11 Cropping Systems Eect onSoil Biological Health andSustainability
Phosphodiesterases in soil and related microorganisms are even less studied.
Considering that the larger input of fresh organic P into the soil is out of the decom-
position of phospholipids and nucleic acids, derived from the phosphodiesterase
activity (Cosgrove 1967, 1980), the research on these topics is clearly underrepre-
sented compared to its importance. For releasing free phosphate from a phosphate
diester, both phosphodiesterase and phosphomonoesterase are required (Turner and
Haygarth 2005). Phosphodiesterase releases by an initial hydrolysis a phosphate
monoester which requires subsequent hydrolysis to release free phosphate. This
second step is carried out by the phosphomonoesterase and creates P available for
biological uptake (Fig.11.3). Arylsulfatase Activity
Arylsulfatase, a widely available soil enzyme, catalyzes the hydrolysis of organic
sulfate ester to phenols and sulfate, or sulfate sulfur (Kertesz and Mirleau 2004;
Utobo and Tewari 2014). The enzyme is found in bacteria strains of Pseudomonas
sp., Actinobacteria sp., Klebsiella sp., and Raoultella sp., as well as in fungi like
Eupenicillium sp. and Trichoderma sp. It is also found in plants and animals
(Nicholls and Roy 1971) and was initially detected by Tabatabai and Bremner
(1970) in soils. The secretion of arylsulfatases into the soil environment is mainly
by bacteria as a response to sulfur limitation, as reported by Das and Varma (2011).
According to the ndings of McGill and Colle (1981) and Klose etal. (1999), the
occurrence of arylsulfatase in various soils is many times correlated with the amount
of microbial biomass and rate of sulfur (S) immobilization. Various soil environment
Fig. 11.3 A simplied conceptual model of plant nutrient uptake by microorganisms through
direct and indirect mechanisms and turnover of organic phosphorus inputs from plants and
microbes in soil
K. Saharan et al .
parameters inuence the release of S from soluble and insoluble sulfate esters and
depend on the type and content of organic matter (Sarathchandra and Perrott 1981),
changes in the pH of the soil (Acosta-Martinez and Tabatabai 2000), heavy metal
content (pollution) or organic sulfate esters concentration, and the extent of protec-
tion against enzymatic hydrolysis of organic sulfate esters, like sorption to particle
surfaces in soils (Joachim and Patrick 2008). By now the knowledge about specic
microbial genera or species having an important role in the soil organosulfur circle
with arylsulfatase as the key enzyme is little (Kertesz and Mirleau 2004). Considering
the importance of sulfate in plant nutrition, the role of arylsulfatase in S mobiliza-
tion in agriculture soils is still a critical factor and requires more attention from the
scientic institutions. Dehydrogenase Activity
Dehydrogenase enzyme is able to oxidize soil organic matter and is seen as an inte-
gral element of intact cells. During the oxidation process, a transfer of electrons and
protons from substrates to acceptors takes place, but the enzyme does not extracel-
lularly accumulate in the soil (Das and Varma 2011). Dehydrogenase activities as
abundant metabolic processes in healthy microorganisms to decompose organic
matter are a general bio-indicator of microbial respiration activities in soils (Bolton
etal. 1985), and this activity can therefore be used to indicate biological soil activity
(Utobo and Tewari 2014). This enzyme requires a bacterium as host and is found
only within certain soil bacteria, e.g., genus Pseudomonas, with most abundant in
Pseudomonas entomophila. The presence of dehydrogenase in soil is therefore a
valid indicator for the presence of soil bacterial cultures (Walls-Thumma 2000).
Addition of triphenyltetrazolium chloride to the soil makes organic materials
more available to microorganisms, and this chloride becomes converted to forma-
zan, a chemical substance which can then be extracted for analysis from the soil.
This test for dehydrogenase activity in soil indicates the presence of healthy bacteria
with higher formazan levels and concludes for active metabolic processes
enhancing the soil fertility (Alef and Nannipieri 1995; Walls-Thumma 2000). This
determination of dehydrogenase levels leads to a more intense understanding of side
effects from agricultural practices as application of articial fertilizers, herbicides,
or pesticides. As a direct indicator of the microbial activity in the soil, it can also
serve as soil pollution indicator. McCarthy et al. (1994) reported higher levels of
dehydrogenase enzyme activities in soils polluted with efuents from pulp and
paper mills but low enzyme activities in y-ash-polluted soils. Similar results are
reported by Pitchel and Hayes (1990). Urease Activity
Urease is the driving and required enzyme for the urea fertilizer hydrolysis into NH3
and CO2, accompanied with the pH rise of the soil and loss of N to the atmosphere
through NH3 volatilization (Frankenberger and Tabatabai 1982). Urease is widely
found as intra- as well as extracellular enzyme in nature, being present mainly in
plants and microorganisms (Burns 1982). Urease extracted from plants or microor-
ganisms degrades rapidly in soil by proteolytic enzymes (Pettit etal. 1976; Zantua
11 Cropping Systems Eect onSoil Biological Health andSustainability
and Bremner 1977). This leads to the conclusion that a relevant share of the soil
ureolytic activity is carried out by extracellular urease, stabilized from the immobi-
lization on organic and mineral soil colloids. Urease activity rises with organic fer-
tilization and reduces with tillage of the soil (Saviozzi etal. 2001), so it is also
widely used for evaluating changes in the soil management related to soil quality.
Soil management-related parameters as soil depth, organic matter content, or crop-
ping history, as well as environmental factors like pH, temperature, or heavy metal
depositions, also inuence the urease activity, which can therefore be used as a
biological indicator of the soil constitution (Yang etal. 2006). The urease activity
depends also on the physical and chemical soil properties and also on the microbial
community (Corstanje etal. 2007). The enzyme stability is inuenced by factors as
humic substances or organo-mineral complexes, which makes it resistant against
denaturation from heat and proteolytic effects (Makoi and Ndakidemi 2008). Urease
activity generally increases with higher temperatures, and temperature dependency
of the urea hydrolysis has drawn a signicant attention in research. A better man-
agement of urea fertilizers requires the intense understanding of urease activity,
especially in warm areas with a high amount of rainfall and irrigated or ooded soil
conditions (Makoi and Ndakidemi 2008). Urease can be produced by bacteria,
yeasts, algae, and fungi, as well as by plants. It may also become synthesized in
some organisms, but mostly urease expression is under nitrogen regulation (Anna
2014). The synthesis of the enzyme is suppressed when growing cells have access
to a preferred source of nitrogen (e.g., NH4+) and activated under availability of
urea or alternative sources of N. N supply regulating role for plants, after urea
fertilization, created high attention for the soil urease activity.
11.4 Cellulose-Degrading Microorganisms
Soil microorganisms exert an important role in the degradation of cellulose.
Cellulose-degrading microorganisms are abundant and ubiquitous in nature. Fungi
or bacteria, including mesophilic or thermophilic anaerobic or aerobic bacteria, are
able to perform the task of degrading cellulose (Wilson 2011). Even though present
in high amounts, only a small fraction of microorganisms are able to degrade cel-
lulose, likely due to its presence in recalcitrant cell walls. Cellulose degradation
follows several mechanisms employed by different types of microorganisms, but all
of them involve cellulases. The plant cell walls, the natural substrate of the cellu-
lases and cellulolytic organisms, turn them to highly diversied organisms. Despite
the great amount of information available, there is still not the full understanding
about the cellulose degradation and microbial ecology in any given environment.
The vast diversity of cellulose-degrading microorganisms in most of the active envi-
ronments and lack of culture techniques to grow them articially still limit our
understanding of these topics. Cellulases are highly diverse enzymes, catalyzing a
single chemical reaction which is the hydrolysis of β-1,4 linkage, joining two
glucose molecules within a cellulose molecule. The fact that cellulases are able to
degrade an insoluble substrate makes them a very unique enzyme (Wilson 2008).
K. Saharan et al .
The enzyme has to diffuse into the substrate and subsequently to move a segment
from a cellulose molecule away from the insoluble particle to its active site. Soluble
substrates are, in contrast, diffusing to the enzyme and bind themselves into the
active site. Also cellulase activities may be used as a primary indicator of some
chemical or physical soil properties and provide strategic support in agricultural soil
management (Joachim and Patrick 2008). Any improved understanding of this
enzyme is of high importance as the cellulose enzymes exert a very important role
in natural cellulose recycling, a globally abundant polymer. With a better under-
standing, it may also be used as a sort of prediction tool in programs to enhance the
soil fertility (Das and Varma 2011).
11.4.1 Cellulose-Degrading Bacteria
The bacteria involved in cellulase enzyme production are classied into aerobic,
e.g., Acinetobacter junii, Bacillus subtilis, Cellulomonas biazotea, Paenibacillus
sp., and Pseudomonas; cellulose; and anaerobic, e.g., Acetivibrio cellulolyticus,
Butyrivibrio brisolvens, and Clostridium thermocellum (Islam and Roy 2018;
Sukumaran etal. 2005; Sadhu etal. 2013).
11.4.2 Cellulose-Degrading Fungi
Fungi-synthesized cellulase enzymes occupy a critical role in recycling C and nutri-
ents and in maintaining soil fertility in nature.
The fungi-based cellulolytic enzyme systems are usually separated into three
groups: (i) soft-rot fungi with members Aspergillus niger, A. oryzae, Fusarium
solani, T. harzianum, Trichoderma reesei, Trichoderma atroviride, and Mucor cir-
cinelloides; (ii) brown-rot fungi with Poria placenta, Coniophora puteana, Lanzites
trabeum, Tyromyces palustris, and Fomitopsis sp.; and (iii) white-rot fungi with
Phanerochaete chrysosporium, Agaricus arvensis, Sporotrichum thermophile,
Pleurotus ostreatus as members (Kleman-Leyer etal. 1996; Nutt 2006; Sukumaran
etal. 2005; Kuhad etal. 2011).
11.5 Phosphatase Activity
Phosphorous (P) represents the second major nutrient element after N in higher
organisms. It is necessary for the growth of the plants and crop yield. However, a
large quantity is immobilized due to the intrinsic characteristics of soils like pH,
affecting the nutrient availability and activity of enzymes and altering the equilib-
rium of the soil solid phase (Martinez-Salgado etal. 2010; Dick and Tabatabai 1983).
Phosphatases are enzymes capable of hydrolyzing phosphoric esters with the
liberation of inorganic phosphate. They can be found widely distributed in the
nature and form two groups, “alkaline” and “acid” phosphatases. Their activity
11 Cropping Systems Eect onSoil Biological Health andSustainability
depends largely on the moisture content in the soil and environmental temperature.
They are usually classied according to their pH optimum as neutral (EC 3.1.3),
alkaline (EC, and acid (EC This classication is driven by the fact
that some are optimally active at an alkaline and some others at an acid pH.Even
though the pH value varies with a given substrate, using phenyl phosphate maxi-
mizes alkaline phosphatase activity at a pH of 9.8, whereas acid phosphatases show
an optimum activity at pH of 4.9. The large spread in between these two optimum
pH values allows determination of one of the phosphatase groups, even in the pres-
ence of the other one.
The phosphatase activity has an important role in the P-conversion, from soil
organic matter into forms of P available for plant uptake, as organisms are only able
to absorb phosphate in dissolved forms (Caldwell 2005). Plant roots, bacteria, and
fungi produce phosphatase enzymes which serve to split off a phosphate group from
its substrates and to convert a complex or an unavailable form of organic P into
available phosphate for plants. The generation of phosphatase is therefore con-
trolled by a combination of demand for P from the plants, microbes, availability of
organic P substrates, and limitation of P the soil. Phosphatase secretions from roots
and mycorrhiza and other enzymes directly inuence the rhizosphere, a narrow soil
region with a dense population of root-associated and free-living microorganisms
(Margalef et al. 2017). Soil contains therefore a large quantity of phosphatase
enzymes, either inside living microbial cells (intracellular enzyme) or as secretion
of living cells or as decayed cellular material (as extracellular enzymes). Stabilization
of phosphatases in soil can be achieved on surface-reactive particles as clay and on
oxides of iron or aluminum. Because of their participation in the phosphorus cycle,
phosphatase enzymes release inorganic phosphate that can be taken up by plants
and microorganisms from organic moiety and complex inorganic materials.
Phosphorus has several important functions in the enumerable metabolic path-
ways and may be described as the maker of the energy currency of living systems
(Ushasri etal. 2013).
11.6 Microbe-Mediated Mineral Solubilization
11.6.1 Nitrogen Solubilizers
Nitrogen forms an inherent component of proteins, nucleic acids, as well as other
essential biomolecules and is therefore among the most important nutrients needed
for the growth of plants and for the productivity in agriculture systems (Bockman
1996). The atmosphere on our Earth contains more than 80% nitrogen, but this is
not directly accessible (is unavailable) for plants. To become available for plants
and other eukaryotes, it must be converted into ammonia. For conversion into
ammonia, three types of processes are possible: (a) atmospheric nitrogen is directly,
in the atmosphere, converted into nitrogen oxides; (b) industrial nitrogen genera-
tion/xation, which involves a high-energy input (due to high process temperatures
of 300–500 °C) and catalyzation to ammonia; and (c) biological nitrogen xation
K. Saharan et al .
(BNF) by microorganisms, using nitrogenase, a complex but natural enzyme sys-
tem. The biological nitrogen xation is environmentally sound and a very suitable
alternative option to chemical fertilizers. This biological process represents also an
important economic factor as about 60% of the available, and nitrogen is xed by
this kind of biological processes. Nitrogen xation in nonleguminous plants is per-
formed by PGPR (diazotrophs), engaging a nonobligate interaction with their host
plant (Glick etal. 1999). A nitrogenase enzyme, coded by nif genes, carries out this
nitrogen xation process (Masepohl and Klipp 1996). Dean and Jacobson (1992)
elucidated the structural composition of the nitrogenase as a two-component metal-
loenzyme consisting of (i) dinitrogenase reductase, the iron protein, and (ii) dinitro-
genase, with a metal cofactor. Masepohl and Klipp (1996) discovered three different
nitrogen-xing systems, based on the metal cofactor: (i) Mo-nitrogenase, (ii)
V-nitrogenase, and (iii) Fe-only nitrogenase. The existence of these nitrogen-xing
systems differs among the bacteria, based on the growing conditions (Bishop and
Jorerger 1990). There are free-living organisms, such as Azospirillum, Azotobacter,
Burkholderia, Herbaspirillum, and Bacillus sp., inhabiting the rhizosphere and
establishing a very close relationship with the plant, although they are not penetrat-
ing the plant tissues (Vessey 2003). They live in sufcient root proximity that the
plants can take up excess nitrogen, xed by the bacteria from the atmosphere but not
used for its own. This unspecic and loose symbiosis is generating an additional
nitrogen source for the plants. BNF is a high energy-consuming process, and bacte-
rial strains which are able to perform this process fulll rst their physiological
needs, creating little leftover nitrogen available for the plants. However, the growth
promotion exerted by nitrogen-xing PGPR was attributed for many years to the
excess N, until additional effects were revealed with the use of nitrogen isotopes in
research. Nitrogen-isotope tracing revealed that free nitrogen-xing bacteria are
enhancing the production of benecial plant growth regulators and xation of
(excess) nitrogen is a secondary benet for the plants (Nakkeeran etal. 2005). These
ndings led to inoculant development and applications, resulting in remarkable crop
yield increases, especially for cereals, with Azotobacter chroococcum and
Azospirillum brasilense as highly important PGPRs. These two species include
strains that are capable to release vitamins and plant growth regulators, exerting
direct inuence on the growth of plants (Nakkeeran etal. 2005).
11.6.2 Phosphorus Solubilizers
The most limiting plant nutrient after nitrogen is phosphorus. Even though P
reserves are abundant, they are not available in a suitable form for plants. Plants can
only absorb soluble mono- and dibasicphosphate forms of P.Of considerable impor-
tance is also P present in organic matter, besides the inorganic forms of soil-stored
phosphorous. Estimations of the deposited organic phosphorus range between 30%
and 50% of the total available P in soil. This reservoir of soil-stored P can become
mineralized by microorganisms and converted into soluble phosphates, suitable for
uptake by plants (Gyaneshwar etal. 2002). Phosphate-solubilizing bacteria employ
11 Cropping Systems Eect onSoil Biological Health andSustainability
two different mechanisms for this conversion: (i) release of organic acids, which
produce ionic interactions with the phosphate salt cations and mobilize the phos-
phorous, and (ii) release of phosphatases which in turn are responsible for fracturing
phosphate groups bound to organic matter (Gyaneshwar etal. 2002). Many micro-
organisms from different genera are capable of solubilizing phosphate and include
the following genera: Pseudomonas, Bacillus, Rhizobium, Burkholderia,
Achromobacter, Agrobacterium, Micrococcus, Aerobacter, Flavobacterium,
Chryseobacterium, and Erwinia.
11.6.3 Potassium Solubilizers
The third major essential plant nutrient in crop production, after N and P, is K.It has
an essential role in the activation of the enzyme and in the protein and photosynthe-
sis and is important for the quality of products. Potassium is a dominant constituent
of several soil minerals (Meena etal. 2015, 2016) as it ranks on seventh place among
all the elements in the earth’s crust. K-bearing minerals can become solubilized by
potassium-solubilizing bacteria (KSB), which convert insoluble forms of K into
soluble forms of K, accessible for uptake by plants. The number of microorganisms
having the ability to solubilize K-bearing minerals as biotite, feldspar, illite, musco-
vite, orthoclase, and mica is large. Among these microorganisms are Acidothiobacillus
ferrooxidans, B. circulans, B. edaphicus, Bacillus mucilaginosus, and Paenibacillus
spp. type. KSB are typically found in all kinds of soils, but their number, diversity,
and capability for K solubilization may vary depending upon the soil structure and
climatic conditions. K release is through dissolving silicate minerals and production
of organic and inorganic acids acidolysis, polysaccharides, complexolysis, chela-
tion, and various exchange reactions. Biological fertilizers based on potassium solu-
bilizers (KSBs) are therefore a viable alternative to chemical fertilizers (Etesami
etal. 2017).
11.6.4 Sulfur Solubilizers
For recycling of sulfur compounds, a group of sulfate-reducing bacteria takes up the
active role. They take up the sulfate as nutrient and reduce it to sulde which is
subsequently utilized in the amino acid synthesis (as cystine or methionine) and to
synthesize sulfur-containing enzymes. In this sulfur transformation process, chemo-
lithotrophic sulfur- and sulfate-reducing bacteria become important actors in the
oxidation and reduction reactions. These reactions generate metabolic energy
through sulde oxidation and dissimilatory sulfate reduction (Muyzer and Stams
2008). Sulfur solubilizer bacteria use the highly oxidized form of sulfur (SO4 2),
also known as sulfate, as the terminal electron acceptor to produce hydrogen sulde
(H2S) during the catabolism of organic matter. The so formed sulde can become
oxidized from chemolithotrophic sulfur-oxidizing bacteria, either in an aerobic way
(Thiobacillus or Beggiatoa spp.) or in an anaerobic process (Chlorobium spp.), to
K. Saharan et al .
elementary sulfur (S°) and SO42. Many different bacteria groups are also involved,
e.g., Desulfuromonas spp. and Desulfovibrio sulfodismutans. Agostino and
Rosenbaum (2018) reported that most cultured sulfur solubilizer microorganisms
belong to four bacterial (Deltaproteobacteria, Nitrospirae, Firmicutes, and
Thermodesulfobacteria) and two archaeal (Euryarchaeota and Crenarchaeota)
11.6.5 Zinc Solubilizers
Zinc, an important micronutrient for human beings, animals, as well as for crops, is
a relevant component of different enzymes which catalyze many metabolic plant
reactions. Zinc plays also a relevant role in the resistance of plants against diseases,
in the photosynthesis, for the cell membrane integrity, in protein synthesis, or in
pollen formation (Gurmani et al. 2012). It also enhances the antioxidant enzyme
level and chlorophyll content within the plant tissues (Sbartai etal. 2011). Zinc also
inuences essential life processes in plants, such as (a) quality of N and protein
uptake (nitrogen metabolism); (b) synthesis of chlorophyll (photosynthesis) and
carbon anhydrase activity; (c) biotic and abiotic stress resistance, i.e., resistance
against oxidative damage (Hussain etal. 2015; Alloway 2008).
Acidication is one of the various mechanisms through which zinc-solubilizing
microorganisms solubilize zinc. Organic acids, produced by these microbes in soil,
sequester the zinc cations and reduce the pH of the soil nearby. Additionally, the
anions are able to chelate zinc and enhance therefore the zinc solubility. The pro-
duction of siderophores and protons or oxido-reductive systems on cell membranes
is another mechanism possibly involved in zinc solubilization (Saravanan et al.
2011); also production of chelated ligands is among them (Chang et al. 2005).
Various biofertilizers as Pseudomonas, Rhizobium strains, Bacillus aryabhattai,
Bacillus sp. and Azospirillum, Oidiodendron maius, etc. have shown enhanced plant
growth and amplied zinc content in plant tissues. Zinc solubilization on lab-scale
is reported from bacterial strains like Pseudomonas aeruginosa, Gluconacetobacter
diazotrophicus, Bacillus sp., Pseudomonas striata, Pseudomonas uorescence,
Burkholderia cenocepacia, Serratia liquefaciens, S. marcescens, and Bacillus
thuringiensis (Kamran etal. 2017).
11.6.6 Iron Solubilizers
Iron is another essential plant nutrient, and iron deciency exhibits metabolic
changes due to its role as a co-factor in numerous enzymes that are essential to
important physiological processes in the plants, like respiration, photosynthesis,
and nitrogen xation. Iron is often unavailable for plants or soil microorganism’s
uptake, despite its abundance in soils. The predominant, in soil available, chemical
form is Fe3+, the oxidized form of iron that reacts to build oxides and hydroxides
which are insoluble and hence inaccessible to plants and microorganisms (Brait
11 Cropping Systems Eect onSoil Biological Health andSustainability
1992; Bultreys etal. 2001). For efcient iron absorption, plants are releasing iron-
chelating organic compounds, thus rendering the insoluble oxides or hydroxides
into soluble forms. The iron then diffuses toward the plant and becomes reduced
and, with an enzymatic system present in the cell membrane, absorbed. Another
strategy for iron uptake is in absorbing a complex, which is formed by Fe3+ and the
organic compound, where the iron is then reduced within the plant and readily
incorporated. There are also bacteria in the rhizosphere which are capable to exu-
date iron-chelating molecules (siderophores) into the rhizosphere, performing
therefore a similar function as the plants (O’Sullivan and O’Gara 1992). Siderophores
are compounds with low molecular weight (usually below 1kDa), containing func-
tional groups that are capable of iron-binding in a reversible way. Catechols and
hydroxamates are the mostly found functional groups, with optimal distances to
bind iron among the groups involved. Bacteria producing siderophore typically
belong to the genus Pseudomonas with pyochelin- and pyoverdine-releasing
Pseudomonas uorescens as the most common type. As these substances show anti-
biotic activity and can improve the plant’s iron nutrition, the rhizosphere bacteria
increase their competitive potential in releasing these compounds (Glick 1995).
Siderophore-producing rhizobacteria also improve the health of plant at different
levels. They can enhance the iron nutrition of the plant, can suppress the growth of
other microorganisms in releasing antibiotic molecules, or suppress pathogen
growth by diminishing the available iron for pathogens, usually fungi that are not
capable to absorb the iron-siderophore complex (Cecile and Philippe 2004).
Siderophores are chromo-peptides consisting of three structural parts, a quinoline
chromophore, a peptide chain, and a side chain. Siderophores are assembled by
nonribosomal, cytoplasmic peptide synthetases resembling the machinery described
for antibiotic synthesis. Biosynthetic enzymes encoding genes are iron regulated
and are often clustered with genes involved in the siderophore uptake (Glick 1995).
Most of the bacterial genes that are involved in the iron assimilation are expressed
only under iron-deciency conditions (Hantke 2001). The mechanism of uores-
cent pseudomonads for siderophore-mediated disease-suppression has been
reviewed by Loper and Buyer (1991). The producing uorescent pseudomonas
strain can use the resulting ferric-siderophore complex via a specic receptor,
located in its outer cell membrane, but the complex is not available to other organ-
isms (Buyer and Leong 1986). The uorescent pseudomonas strain may inhibit the
growth of harmful bacteria and fungi at the plant root, as well as reduce or prevent
the germination of fungal spores due to iron starvation conditions. A model for uo-
rescent pseudomonas siderophores-induced root pathogens suppression is shown in
The unavailability of the ferric iron in the soil restricts the growth of deleterious
or harmful organisms (Saharan etal. 2010; Daniel etal. 1992). Iron deciency or
deprivation leads to a kind of chlorosis in plants. Reports show (Moores etal. 1984)
that the uorescent siderophores from Pseudomonas spp. strain B10 inhibit the
uptake of iron by maize plants and peas. In contrast, there are also numerous reports
suggesting that plant species are able to obtain iron from certain microbial sidero-
phores. Iron, derived from microbial hydroxamate siderophores, may become
K. Saharan et al .
accessible for plants, in nutrient solution as well as in soil. Furthermore, uorescent
pseudomonad siderophores have also been implicated in the remedy of lime-induced
chlorosis by peanuts or in the iron uptake of tomato plants (Persello-Cartieaux etal.
2003; Lemenceau etal. 1993). Figure11.5 shows the mechanisms of iron removal
from siderophore complex by plants (Clarke etal. 2001), indicating that some plant
species may acquire the needed iron via certain microbial siderophores. The sidero-
phore concentration in soil is approximately in the range of 10–30 M.
11.7 Soil Respiration
Soil respiration is among the most important soil biological indicators that reect
the biological activity within the soil. The microbial activity is a fundamental pro-
cess, providing energy and nutrients for recycling processes in an ecosystem. This
is because soil microorganisms have some highly relevant roles in the bio-
geochemical cycling of organic C, N, P, K, S, etc. (Maharana and Patel 2013;
Bandick and Dick 1999). High microbial respiration indicates loss of valuable
organic carbon and low nutrient cycling activity in the soil (Alef 1995; Pankhurst
etal. 1997), whereas low microbial respiration indicates immobilization and/or the
presence of pollutants such as fungicides or pesticides (Pankhurst etal. 1997). Soil
Fig. 11.4 Model for suppression of root pathogens by siderophores from uorescent
11 Cropping Systems Eect onSoil Biological Health andSustainability
microbial respiration has a linear relationship with mineralization of soil organic
matter (SOM). Respiration is estimated as either CO2 production or O2 consump-
tion, using basal respiration such as short-term laboratory assays (Parkin etal.
1996). In general, changes in precipitation, management practice, microbial com-
munity structure, aeration, soil structure, nutrient conditions, and pH affect the soil
microbial respiration (Anderson and Domsch 1993; Singh etal. 2011). In addition,
respiration is a temperature-sensitive process and has a close relationship with cli-
mate change and global C cycling. According to reports, soil provides a very large
sink of carbon (C) in the terrestrial ecosystems and makes a major contribution to
the global carbon equilibrium. The agricultural soil takes up an important role in the
cycle of global carbon and accounts for around 11% of the global anthropogenic
CO2 emissions, as reported by Gao etal. (2013). To minimize the soil respiration
and to retain more C sequestered in agricultural soils is therefore of high impor-
tance. Autotrophic respiration from plant roots and heterotrophic respiration of
plant residues, root litter, and exudates as well as soil organic matter by soil micro-
organisms are the main contributor to soil respiration. Tillage practices in cropland
and straw management is affecting the soil respiration in a large amount. The largest
increase is observed directly after tillage operations; hence reducing the tillage-
intensity can therefore lower the cumulative CO2 emissions in a signicant amount
(Gao etal. 2013).
Fig. 11.5 Mechanisms of removal of iron from the siderophore complex by reduction of Fe3+.
Mechanisms 1 and 2 are used by plants. Microorganisms use any of the three stated mechanisms.
(Saharan etal. 2010; Clarke etal. 2001)
K. Saharan et al .
11.8 Conclusion
The balanced interaction between plants, plant nutrients, soil, and soil-borne micro-
organisms is an important factor for the performance of the agriculture system. Soil
nutrients are consumed during plant growth and must be replenished for a sustain-
able agricultural growth cycle. This can be done by donation of articially created
nutrients (e.g., chemical fertilizer), by recycling plant material, by donating con-
verted plant material (manure), and other forms of organic residues or any combina-
tion of these. Soil-borne microorganisms have a key role in preparing and converting
available nutrients into a plant accessible form, as many nutrients are not in a for
plants “ready-made” form present in the soil. One such group are the mineral solu-
bilizers; they convert minerals into plant-accessible forms. Other microorganisms
can, for example, x atmospheric nitrogen, a major nutritional element for all plants.
Atmospheric nitrogen can also be xed by plants from the legume group. They form
therefore an important factor within a sustainable agriculture system, with minimal
external fertilizer input. Recycling organic material as fertilizer involves cellulose
degradation. Again, we nd microorganisms in the form of bacteria and fungi per-
forming this task. The soil itself represents the host of all these activities. It provides
the physical structure needed for the plants to grow, supplies the nutrients and water,
and is home of the microorganisms. A healthy soil is therefore the key element for
a sustainable agriculture system. The soil status (health) can be expressed in various
ways, and there is still no common denition and metric for measuring and classify-
ing the quality status of the soil health. Soil health indicators, such as soil microbial
biomass or soil nutrient content (e.g., N, P, and K), are direct measurable parame-
ters, giving a measure about the physical status of the soil. Another group of soil
health indicators is an enzymatic activity parameter, revealing the status of the
microbial activity, the “living part” in the soil. Many research studies indicate that
not only proper physical soil parameters are sufcient for a solid agricultural base,
but also the microbe system plays at least the same important role, and this must be
considered in all aspects of research and farming. All these parameters are inu-
enced by the agriculture system applied on the soil, the cropping system. There is
no general optimum cropping system, as the climate zone, the soil structure, and
many other parameters determine the growing sequence and cycle on a particular
land area. Also the human factor must be considered as an inuencer of the ideal
cropping system for a given area, as the available input (labor, machinery, fertilizer,
etc.) and the requested output (the return from the agricultural activities) are a key
factor determining the soil state and the entire soil ecosystem in a holistic way.
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... The content of exchangeable potassium in the soil at a constant level was determined six years after the application of biomodified organo-mineral fertilizer with a decrease in К2О in the control variant (Fig. 3). The prolonged effect of fertilizers is probably associated with the synergistic interaction of fertilizers and the microbiological component of the preparation, as well as the biosolubization of hard-to-reach forms of potassium by bacteria of the genus Bacillus, which was previously identified by researchers [11,16,17]. ...
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The crucial trend in the intensification of gardening is the use of agrochemicals, including the systematic application of mineral fertilizers, regulated by the production flow chart of fruit products. Technological pressure on the soil causes aggravating the ecological problem of loss of the fertility level in the conditions of the orchard monoculture. The search for sustainable and environmentally effective approaches to solving the problem of managing fertility factors is aimed at studying the effects of biological and biomodified fertilizers. The changes in the main indicators of the effective fertility of the structural-metamorphic agrosem in the conditions of the orchard monoculture with the application of biomodified organo-mineral fertilizer were studied in dynamics. The prolonged effect of organo-mineral fertilizer on increasing the content of the main indicators of effective fertility in the soil was determined six years after application. The use of biomodified organo-mineral fertilizer in the orchard fertilization system is considered as an element of an integrated strategy for the management of orchard soil fertility.
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Climate change poses a significant risk to food security. Recent floods in Pakistan could serve as an example. In the current climate change scenario, there is a dire need to develop methods that increase crop productivity and reduce the threat of food insecurity in areas with low crop production. A detailed field experiment was conducted to check the effects of intercropping and straw mulching under conventional tillage (CT) and no tillage (NT) systems on soil health indicators and cotton productivity at the experimental area of Khwaja Fareed University of Engineering and Information Technology (KFUEIT), Rahim Yar Khan, Pakistan. The main plot treatments comprised CT and NT. The subplot treatments were sole cotton (C1), cotton + mung-bean intercropping (C2), cotton + mung-bean + straw mulching (C3) and cotton + straw mulching (C4) under CT, while sole cotton (N1), cotton + mung-bean intercropping (N2), cotton + mung-bean + straw mulching (N3) and cotton + straw mulching (N4) were the NT subplot treatments. Overall, NT increased plant height by 18.4 %, chlorophyll a and b contents by 28.2 and 21.1%, respectively, mean boll weight by 17.9%, and seed yield by 20.9% compared to CT (P < 0.05). The interaction of tillage and mulching increased plant height by 7.0% under CT and 21.8% under NT in comparison with no mulching. Similarly, straw mulching under NT increased chlorophyll a and b contents by 41.9 and 28.5%, respectively, mean boll weight by 26.9%, and cotton seed yield by 23.0% in comparison with no mulching under NT. Intercropping decreased crop yield without straw mulching but increased it under straw mulching. Further, straw mulching increased soil physicochemical properties under NT, which contributed to increasing crop productivity. We concluded that straw mulching under NT might be a promising practice for enhancing cotton yield, productivity, and soil health in low-productivity areas.
Sulfur (S) is the most versatile element among those commonly occurring in plants. It is the reduced S that essentially becomes the moiety for organic residue constituents in biomolecules. The bio-sensitive pathway for S assimilation not only works its demand to cultivate but also for regulation of different metabolic reaction. In plant system starting from cell membrane residues to different signaling compounds, S becomes most important element in maintenance of homeostasis under stress condition. Sulfolipid, sulfoprotein, and other secondary S compounds rank this element to carry messages about enzymatic steps. This is mostly concern with multiple oxidation state of S along with a significant release of free energy which makes the sulfate assimilation more favorable. Therefore, facing abiotic stress with reference to oxidative exposure plants is significantly in debt to S metabolism. This mini chapter is expected to satisfy the S involvement in various corners of cellular and biochemical reactions those let accomplish plant successful stress tolerance.
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OBJECTIVES: This study was conducted to isolate, screening and purification of cellulase from bacteria present in sugar industry waste (molasses) and characterization by morphological and biochemical analysis. RESULTS: Based on experiments, three bacterial strains produced clear transparent zone into carboxymethyl cellulose (CMC) agar plate were identified as cellulase producing bacteria. Different culture parameters such as pH, temperature, incubation period, substrate concentration and carbon sources were optimized for enzyme production. According to the morphological and biochemical tests, the isolated strains were identified as Paenibacillus sp., Bacillus sp. and Aeromonas sp. The first strain Paenibacillus sp. showed high potentiality for maximum cellulase production (0.9 µmol ml-1 min-1) at pH 7.0 after 24 h of incubation at 40 °C in a medium containing 1.0% CMC. Then Paenibacillus sp. was selected for enzyme purification by ammonium sulfate precipitation, DEAE-cellulose and CM-cellulose column chromatography, respectively. In last step of purification, specific activity, recovery and purification fold were 2655 U/mg, 35.7% and 9.7, respectively. The molecular weight of the purified cellulase was found to be 67 kDa by SDS-PAGE, had an optimal pH and temperature at 7.0 and 40 °C. According to substrate specificity, the purified cellulase had high specificity on CMC substrate which indicated it to be an endo-β-1,4-glucanase.
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Electroautotrophs are microbes able to perform different biocathodic reactions by using CO2 as sole carbon source and electrochemical reducing power as a sole energy source. Electroautotrophy has been discovered in several groups of microorganisms, including iron-oxidizing bacteria, iron-reducing bacteria, nitrate-reducing bacteria, acetogens, methanogens and sulfate-reducing bacteria. The high diversity of electroautrophs results in a wide range of Bioelectrochemical Systems (BES) applications, ranging from bioproduction to bioremediation. In the last decade, particular research attention has been devoted toward the discovery, characterization and application of acetogenic and methanogenic electroautotrophs. Less attention has been given to autotrophic sulfate-reducing microorganisms, which are extremely interesting biocatalysts for multiple BES technologies, with concomitant CO2 fixation. They can accomplish water sulfate removal, hydrogen production and, in some case, even biochemicals production. This mini-review gives a journey into electroautotrophic ability of sulfate-reducing bacteria and highlights their possible importance for biosustainable applications. More specifically, general metabolic features of autotrophic sulfate reducers are introduced. Recently discovered strains able to perform extracellular electron uptake and possible molecular mechanisms behind this electron transfer capacity are explored. Finally, BES technologies based on sulfate-reducing electroautotrophs are illustrated.
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An increase in intensive cropping would benefit society by providing food to a growing population, and vegetable production is an excellent example of intensive cropping systems that are indeed on the rise. Vegetable cropping systems are high-input and generally require large quantities of fertilization, frequent irrigation, and repeated tillage operations. Consequently, an increase in global vegetable production may have seriously negative impacts on soil health and ecosystem services. Yet, not only maintaining but improving soil health is critical to enhancing the sustainability of food production systems. Previous agricultural research mainly focused on field crop systems and largely ignored vegetable cropping systems; consequently, this represents a conspicuous research gap, one that must be addressed in order to make progress toward sustainable food production. Here, we review the literature to gain a better understanding of how management has influenced various soil health indices (soil biology, chemistry, and physical dynamics) and to evaluate the implications for soil ecosystem services in vegetable cropping systems. We found that alternative modifications to conventional vegetable production systems, which resemble methods used in organic or conservation agriculture, tended to improve aspects of soil health. For example, soil amendments generally improved soil chemical and nutrient indices of health—soil carbon levels and nitrogen reserves in particular. Incorporation of cover crops to vegetable crop rotations tended to improve nitrogen recycling via reduced nitrate leaching risks, increased soil carbon levels, and weed suppression. Reduced tillage systems were rare, presenting an important challenge and opportunity for further improving soil health dynamics in vegetable production. Notably, adopting alternative practices generally had no effect on crop yields, which implies little risk of yield penalties when agronomic management is carefully planned. Our results indicate that future sustainable vegetable cropping systems may embody a blend between organic and conventional ideologies to better maintain or improve soil ecosystem functioning.
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The impacts of continuous cropping of banana on soil microbiological and biochemical properties are little understood. In this study, we evaluated the variations in soil bacterial community abundance and diversity, microbial biomass carbon (MBC) and nitrogen (MBN) as well as soil enzyme activities involved in C, N and P cycles as affected by continuous cropping of banana. An initial increase in bacterial 16S rRNA copy and soil microbial biomass was observed in the second cropping and then decreased until the fourth cropping. The diversity of bacterial community showed a continuous decrease throughout the experiment. In addition, continuous cropping of banana caused shifts in bacterial community composition and structures. Soil urease and invertase exhibited the highest activities in the second cropping and then decreased gradually from the second to the fourth cropping. The phosphatase activity showed a gradual increase from the first to the third cropping. The bacterial 16S rRNA copy was positively correlated with the contents of MBN and urease activities. The results indicated that continuous cropping of banana was responsible for the disturbance of the bacterial community and that the effect on enzyme activity varies depending on the type of soil enzyme.
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Soil microbial biomass has been used as an early indicator of change in soil properties resulting from urbanization. We analyzed the effect of urbanization along a rural–urban gradient on soil microbial biomass and physico-chemical properties of the soil. The mean microbial biomass carbon (MBC) value were 107.4, 121.3, and 134.2 μg g⁻¹ of soil, respectively, for urban, sub-urban and rural sections of the gradient. Whereas, the mean microbial biomass nitrogen (MBN) was 10.2, 11.5, and 12.5 μg g⁻¹ of soil for urban, sub-urban, and rural gradient. Similarly, the mean values of microbial biomass phosphorus (MBP) were 5.1, 5.8, and 6.3 μg g⁻¹ of soil, for urban, sub-urban, and rural gradient, respectively. ANOVA and Tukey’s Honest Significant Difference (HSD) analyses showed significant difference (P ≤ 0.05) in microbial biomass with physico-chemical characteristics of soils. Maximal soil microbial biomass was reported for rural soils followed by sub-urban and urban soil. Disturbance in soil texture, increased in BD and decrease in soil moisture content as major factors responsible for depletion in soil microbial biomass in urban soils. . Thus, suggesting that the urbanization adversely effected soil microbial biomass by altering natural soil characteristics.
Certain members of the fluorescent pseudomonad group have been shown to be potential agents for the biocontrol of plant root diseases. The major problems with the commercialization of these beneficial strains are that few wild-type strains contain all the desired characteristics for this process and the performance of strains in different soil and climatic conditions is not reproducible. Consequently, prior to selection and/or improvement of suitable strains for biocontrol purposes, it is necessary to understand the important traits required for this purpose. The production of fluorescent siderophores (iron-binding compounds) and antibiotic compounds has been recognized as important for the inhibition of plant root pathogens. Efficient root colonization is also a prerequisite for successful biocontrol strains. This review discusses some of the characteristics of fluorescent pseudomonads that have been suggested to be important for biocontrol. The genetic organization and regulation of these processes is also examined. This information is necessary for attempts aimed at the improvement of strains based on deregulating pathways or introducing traits from one strain to another. The release of genetically engineered organisms into the environment is governed by regulations, and this aspect is summarized. The commercialization of fluorescent pseudomonads for the biological control of plant root diseases remains an exciting possibility. The understanding of the relevant characteristics will facilitate this process by enabling the direct selection and/or construction of strains which will perform under a variety of environmental conditions.
Continuous rice-wheat (RW) rotation with conventional agronomic practices has resulted in declining factor productivity and degrading soil resources. A farmer's participatory research trial was conducted in Karnal, India to evaluate 8 combinations of cropping systems, tillage, crop establishment method and residue management effects on key soil physico-chemical and biological properties. Treatments (T) 1–4 involved RW and 5–8 maizewheat (MW) with conventional tillage (CT) and zero tillage (ZT) with (+R) and without (−R) residue recycling. Residue was either incorporated (Ri) or mulched (Rm). Treatment 1 (RW/CT − R) had the highest bulk density (BD) (1.47 Mg m−3 ) and T8 (MW/ZT + Rm), the lowest (1.34 Mg m−3 ). After 3 years of cropping, soil accumulated more organic C in (a) MW (9.33 Mg ha−1 ) than RW (8.5 Mg ha−1 ), (b) ZT (9.25 Mg ha−1 ) than CT (8.58 Mg ha−1 ), and (c) + R (10.18 Mg ha−1 ) than –R (7.65 Mg ha−1 ). MW system with ZT and residue (T8: MW/ZT + Rm) registered 208, 263, 210 and 48% improvement in soil microbial biomass C (MBC) and N, dehydrogenase activity (DHA) and alkaline phosphatase activity (APA), whereas RW system in T4 (RW/ ZT + Rm) registered 83, 81, 44 and 13%, respectively as compared with T1 (RW/CT − R), the business as usual scenario. Treatment 8 (MW/ZT + Rm) recorded the highest microbial population viz. bacteria, fungi and actinomycetes. The most abundant micro-arthropods present in the soil of experimental plot were Collembola, Acari and Protura which varied with treatments. Soil MBC, APA, BD and micro-arthropod population were identified as the key indicators and contributed significantly towards soil quality index (SQI). MW system with ZT and Rm (T8) recorded the highest SQI (1.45) followed by T6 (1.34) and the lowest score (0.29) being in T1 (RW/ CT − R). The SQI was higher by 90% in MW compared to RW, 22% in ZT compared to CT, and 100% in residue recycling compared with residue removal. System yield was strongly related to key soil quality indicators and also positively correlated with SQI. Longer-term studies are essential to realize maximal effects of improvements in soil health on crop yields.
Conservation agriculture (CA) practices such as zero tillage (ZT) and permanent raised beds (PB) accelerate deposition of soil organic matter and augment associated biological properties of soil through enhanced inputs of organic carbon. However, the potential benefit of CA under intensive cereal‐based systems for key soil health indicators (such as carbon pools and biological activities) is only partially known. Therefore, we analysed the effect of three medium‐term tillage practices and four intensive crop rotations on selected soil organic carbon pools and microbial properties. The tillage practices consist of ZT, PB and conventional tillage (CT) in main plots and four crop rotations (MWMb, maize–wheat–mungbean; MCS, maize–chickpea–Sesbania; MMuMb, maize–mustard–mungbean; MMS, maize–maize–Sesbania) in subplots. The experimental design was split‐plot with three replications. After 6 years, we observed a significant positive effect of CA practices on soil organic carbon (SOC) content, labile SOC fractions, soil microbial biomass carbon (MBC) and dehydrogenase activity (DHA). The total organic carbon (TOC) was greatly affected by medium‐term tillage and diversified cropping systems; it was larger for CA and MCS and MWMb systems. The interaction effect between tillage and cropping systems for SOC content was not significant at all soil depths. Significantly larger contributions (8.5–25.5%) of labile SOC pools to TOC at various soil depths were recorded in PB and ZT. There was a significant positive effect of CA practices and diversified crop rotations on MBC and DHA at all the soil depths and sampling times, but the interaction effect between tillage and cropping systems was not significant. Thus, our medium‐term (≥ 5‐years) study showed that the combination of CA (PB and ZT) practices and appropriate choice of rotations (MCS and MWMb) appears to be the most appropriate option for restoration and improvement of the soil health of light‐textured Inceptisols through the accumulation of soil organic matter (SOM) and improvement in soil biological properties. Highlights • Effect of conservation agriculture (CA) on soil labile carbon inputs and biological properties. • Observed changes in SOC stock and C‐pools at different soil depths after 6 years. • Significant effects of tillage and crop rotations observed for labile‐C pools. • Adoption of ZT and PB enhanced SOC stock, C‐pools and microbial activity compared to CT.