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Abstract

Algae are a large and diverse group of microorganisms that can carry out photosynthesis since they capture energy from sunlight. Algae play an important role in agriculture where they are used as biofertilizer and soil stabilizers. Algae, particularly the seaweeds, are used as fertilizers, resulting in less nitrogen and phosphorous runoff than the one from the use of livestock manure. This in turn, increases the quality of water flowing into rivers and oceans. These organisms are cultivated around the world and used as human food supplements. They can produce a clean and carbon-neutral food also and can be grown on abandoned lands and arid desert lands with minimal demands for fresh water. Seaweeds are an important source of iodine. Iodine levels in milk depend on what the cow producing the milk has been fed with. Feeding milk cattle with seaweeds can increase the quantity of iodine in milk, according to Fuzhou Wonderful Biological Technology. Egg-laying rate in hen is also increased by algae feed additives. In this article, we discussed the most important aspects of algae and its agricultural uses to those who work in this area.
African Journal of Biotechnology Vol. 11(54), pp. 11648-11658, 5 July, 2012
Available online at http://www.academicjournals.org/AJB
DOI: 10.5897/AJB11.3983
ISSN 16845315 © 2012 Academic Journals
Review
Agricultural importance of algae
Abdel-Raouf N.1, Al-Homaidan A. A.2 and Ibraheem I. B. M.2,3*
1Department of Botany and Microbiology, Faculty of Science, Medical Studies and Sciences Sections, King Saud
University, Riyadh, Saudi Arabia.
2Department of Botany and Microbiology, Faculty of Science, King Saud University, Riyadh, Saudi Arabia.
3Department of Botany, Faculty of Science, Beni-Suef University, Beni-Suef, 62511, Egypt.
Accepted 8 June, 2012
Algae are a large and diverse group of microorganisms that can carry out photosynthesis since they
capture energy from sunlight. Algae play an important role in agriculture where they are used as
biofertilizer and soil stabilizers. Algae, particularly the seaweeds, are used as fertilizers, resulting in
less nitrogen and phosphorous runoff than the one from the use of livestock manure. This in turn,
increases the quality of water flowing into rivers and oceans. These organisms are cultivated around
the world and used as human food supplements. They can produce a clean and carbon-neutral food
also and can be grown on abandoned lands and arid desert lands with minimal demands for fresh
water. Seaweeds are an important source of iodine. Iodine levels in milk depend on what the cow
producing the milk has been fed with. Feeding milk cattle with seaweeds can increase the quantity of
iodine in milk, according to Fuzhou Wonderful Biological Technology. Egg-laying rate in hen is also
increased by algae feed additives. In this article, we discussed the most important aspects of algae and
its agricultural uses to those who work in this area.
Key words: Algae, seaweeds, agriculture, biofertilizer, soil stabilizers.
INTRODUCTION
The assemblage of plant-like forms which are collectively
referred to as algae includes a tremendously diverse
array of organisms. Algae may range in size from single
cells as small as one micrometer to large seaweeds that
may grow to over fifty meters (Vymazal, 1995). Many of
the unicellular forms are motile, and many integrate the
protozoa (South and Whittick, 1987). Algae are
ubiquitous; they occur in almost every habitable environ-
ment on earth, in soils, permanent ice, snow fields, hot
springs, and hot and cold deserts. Biochemically and
physiologically, algae are similar in many aspects to other
plants. They possess the same basic biochemical
pathways; all possess chlorophyll-a and have carbo-
hydrate, protein and products comparable to those of
higher plants. Furthermore, algae are the major primary
producers of organic compounds; and play a central role
as the base of the food chain in aquatic systems. Besides
forming the basic food source for these food chains,
*Corresponding author. E-mail: ibraheemborie@hotmail.com.
they also produce the oxygen necessary for the
metabolism of the consumer organisms (Lee et al.,
1989).
This review intends to reinforce the notion that algae
are important components of arid and semi-arid
ecosystems. Furthermore, their distribution and condition
may indicate the health of the environment. Additionally,
the presence of algae leads to reduced erosion by
regulating the water flow into soils. Similarly, they play a
role in soil fertility, soil reclamation, bio-controlling of
agricultural pests, formation of microbiological crust,
agricultural wastewater treatment and recycling of treated
water. Human civilization depends on agriculture for its
existence. The success of agriculture greatly depends on
the fertility level of the soil. Like other organisms, algae
which are found in different soil types, may help the soil
to improve its characteristics such as, carbon content,
texture, aeration (Ibraheem, 2007) and also nitrogen
fixation (Hamed, 2007). The magnitude of these
improvements is greatly dependent on the physical and
chemical characteristics of the soil, affecting the composition
of the algal population (Abdel-Raouf et al., 2004).
Marine algae are used as fertilizers on farmlands close
to the sea, examples include the large brown and red
algae used as organic fertilizers; which are usually richer
in potassium but poorer in nitrogen and phosphorus
(Waaland, 1981). The weed is usually applied direct and
ploughed in, both as solid (processed into a seaweed
meal) and/or as liquid fertilizer (concentrated extract of
seaweeds) (Round, 1973). Probably the widest use of
seaweeds in agriculture is as liquid fertilizers (Povolny,
1981). The positive effect of liquid fertilizers is mainly
explained by the high content of trace elements and
growth regulatory substances (particularly cytokinins).
Calcareous red algae known as maerl, are used in the
United Kingdom and France to reduce soil acidity
(Blunden et al., 1981). Man’s uses of algae, particularly
marine algae, are far more diverse and economically
important than generally realized (Abbott and Cheney,
1982). They are used as human food, in agriculture
(fertilizer, manure, fodder and aquaculture), medicine,
textile, paper and paint industries, chemical extracts from
larger marine algae (example alginic acid , carrageenan
or agar) are used in the manufacture of food industry,
and diatomaceous earth (deposits of diatom frustules) is
widely used as filtration and polishing materials. Algae
are also important surface-binding agents which reduce
erosion and can be used for wastewater treatment.
Cyanobacteria are a diverse group of prokaryotes. A
common feature is their oxygenic photosynthesis, which
is similar to that in algae and higher plants. As sunlight is
their energy source and water, they generate oxygen in
the light. Energy and reductants generated by photo-
synthesis are usually used for carbon dioxide reduction.
These microorganisms are distributed worldwide and
improve the growth and development of the plants, with
which they share the habitat, because they: 1) contribute
to soil fertility in many ecosystems; 2) produce various
biologically active substances and 3) have higher
efficiency in biosorption of heavy metals (bioremediation)
(Ibraheem, 2007).
IMPROVEMENT OF SOIL FERTILITY
Some cyanobacteria are able to reduce atmospheric
nitrogen to ammonia, a process where oxygen evolved
by photosynthetic activity in the same cell is detrimental
to nitrogen fixation. Strategies to avoid oxygen range
from temporal separation of nitrogen fixation and oxygen
evolution (in many unicellular and filamentous, non
heterocysts strains) to spatial separation and cellular
differentiation into nitrogen fixing heterocysts (in
filamentous cyanobacteria). Heterocysts are terminally
differentiated cells whose interior becomes anaerobic,
mainly as a consequence of respiration, allowing the
oxygen-sensitive process of nitrogen fixation to continue.
The regulation of dinitrogen fixation has been extensively
studied in the heterocyst system (Bhme, 1998).
Abdel-Raouf et al. 11649
Diazotrophic cyanobacteria require sunlight as a sole
energy source for the fixation of carbon and nitrogen.
Therefore, they have great potential as biofertilizers, and
their use will decrease fuel demand for fertilizer pro-
duction. The agronomic potential of heterocystous
cyanobacteria, either free-living or in symbiotic
association with water fern Azolla, has long been
recognized (El-Zeky et al., 2005). This had led to the
development of small scale biotechnology involving the
use of paddy soils with appropriate cyanobacterial strains
as biofertilizers in rice fields, as has been reported in
China, Egypt, Philippines and India.
Cyanobacteria are congenial biofertilizers for rice
based cropping systems, being the major components of
wetland rice ecosystems which are easily available and
serve as the cheapest sources of natural biofertilizers
(Omar, 2000; Ladha and Reddy, 2003). Whereas the in-
corporation of genes into rice plants by using tissue
culture and modern genetic tools remains as an
ambitious research goal, the use of cyanobacterial
diazotrophic technology in rice agriculture offers an
immediate and even long term alternative to synthetic
nitrogen fertilizers, particularly in developing countries
and the world as a whole. However, one of the weak-
nesses in the technology is the heavy application of
several toxic agrochemicals, especially herbicides, which
are reported in most cases as inhibitors of cyanobacterial
diazotrophic growth, and in some cases as mutagenic.
Therefore, a successful biotechnology requires the
selection of suitable diazotrophic strains as biofertilizers
that could tolerate the field-dose concentrations of
herbicides (Tiwari et al., 1991).
Uptake of P and N
Cyanobacteria also have some soil phosphate-
solubilizing species. Phosphorus (P) is the second
important nutrient after nitrogen for plants and
microorganisms. Most aquatic systems are resource-
limited, where P and N are often the primary limiting
nutrients. To ensure survival, a competitor must be able
to maintain net population growth at resource levels less
than those required by other species (Scott et al., 2005;
Silke et al., 2007). Algae are particularly adapted to
scavenge their environments for resources through
structural changes, storage or increased resource
utilization efficiency (Singh and Dhar, 2007). Internal
adjustments by algae involve biochemical and
physiological adaptations, whilst they can also excrete
substances to enhance nutrient availability. Algae excrete
extracellular phosphatases almost immediately upon the
onset of P limited conditions (Healy, 1973). Algae can
also excrete other compounds and change the pH of their
surroundings, which in turn can render adsorbed P
available (Grobbelaar, 1983). In addition, algae can store
resources like P in excess of their immediate needs. This
11650 Afr. J. Biotechnol.
excess or "luxury" uptake is clearly distinct from the
Michaelis-Menten Monod, 1950) nutrient uptake kinetics
which are based on external resource concentrations.
Epply and Strickland (1968) concluded that the growth
rate of phytoplankton is more closely related to the
cellular nutrient content than to external concentrations. It
is, therefore, necessary to establish a relationship
between the cell quota of a nutrient and the growth rate
of an alga. Such a relationship was given by Droop
(1983).
Cyanobacterial fertilization has been compared to
inorganic fertilization on rice and lettuce seedlings
(Ibraheem, 2007). Biofertilizers are likely to assume
greater significance as complement and/or supplement to
chemical fertilizers in improving the nutrient supplies to
cereal crops because of high nutrient turn-over in cereal
production system, exorbitant cost of fertilizers and
greater consciousness on environmental protection
(Ahmed, 2009).
Nitrogen fixation
Algae, especially cyanobacteria, may be the most
important nitrogen-fixing agents in many agricultural soils
(Rodrigo and Eberto, 2007). Their importance as nitrogen
fixers in rice fields have been studied by several
investigators (Hung and Chow, 1988). The great majority
of cyanobacteria that fix nitrogen are probably hetero-
cystous (Granhall and Henriksson, 1969); however, non-
heterocystous cyanobacteria fix nitrogen as well (Kallas
et al., 1983). The nitrogen fixed by the algae is liberated
and then re-assimilated by the higher plants (Stewart,
1970). A large variety of cyanobacterial species are
known to be nitrogen fixing and their importance in
improving soil fertility for sustainable agriculture in
submerged and irrigated rice cultivation is well
recognized (Saikia and Bordoloi, 1994). The use of
cyanobacteria as a biofertilizer for rice fields is very
promising but limited due to fluctuation in quality and
quantity of inoculum and its physiological attributes in
varied agroecological regions. Utilization efficiency of
fixed nitrogen by rice plants is often low and efforts are
therefore being extended to isolate suitable strains of
cyanobacteria that would be prolific not only in fixing
atmospheric nitrogen but also in excreting it continuously,
thus making it available to the growing rice plants
(Boussiba et al., 1984).
Cyanobacteria are widely used in rice fields throughout
Asia, where their enhancement of soil fertility by means
of biological nitrogen fixation (so called algalization) in
place of N-rich fertilizers (Halperin et al., 1981), but their
beneficial effects is not limited to that. The cyano-
bacterium Tolypothrix tenuis is grown in cultures and
added to rice fields. Aboul-Fadle et al. (1967) reported
that inoculation at about 250 g dry mass ha-1 of the same
species resulted in a 19.5% increase in rice yield as
compared with 16.6% produced by a dressing of 25 kg
ha-1 of ammonium sulfate. In Japan, rice fields are
fertilized by water fern Azolla which multiplies rapidly and
contains the symbiotic blue-green alga Anabaena which
fixes gaseous N2.
Source of organic matter
Algae are also important source of organic matter in soil
(Shields and Durrell, 1964; Ibraheem, 2007). The organic
matter formed from the death and decay of algae may get
mixed in the soil and mucilage acts as binding agent for
soil texture, thereby increasing the humus content and
making it more habitable for other plants after some
years (Marathe and Chandhari, 1975). Humus accumu-
lation is also important for moisture retention (Bolyshev
and Novichkova-Ivanova, 1978). In the U.S.S.R.,
filamentous forms of the Cyanophyceae, especially
Oscillatoria, Schizothrix and Plectonema were found to
be important in soil formation (Gayel and Shtina, 1974).
In most cases, it is generally accepted that the
incorporation of organic carbon via photosynthesis and of
organic nitrogen via nitrogen fixation is the most
important contributions of algae added to the soil. They
also act as a reserve of inorganic nutrients.
Soil reclamation
The difficulties in soil reclamation in arid and semi-arid
regions are mostly the salinity conditions of large soil
areas. Several studies have been carried out on the
effect of salinity on the growth, metabolism and yield of
the plants and algae (Ibraheem and Abdel-Raouf, 2001;
Tang et al., 2007). Some growth regulators such
gibberellic acid (GA3) were used for improving the salt
tolerance of the plants (Ouda et al., 1991). From an
economic point of view, growth regulators are expensive
and are non-practical especially, when applied in large
amounts. Algae play an economic role in soil reclamation
increases soil fertility and improve the plant conditions
under certain environmental factors (Pandey et al., 2005;
Nisha et al., 2007; Prabu and Udayasoorian, 2007).
PRODUCTION OF EXTRACELLULAR SUBSTANCES
Cyanobacteria excrete a great number of substances that
influence plant growth and development (Haroun and
Hossein, 2003; Rodriguez et al., 2006). These micro-
organisms have been reported to benefit plants by
producing growth-promoting regulators (the nature of
which is said to resemble gibberellin and auxin), vitamins,
amino acids, polypeptides, antibacterial and antifungal
substances that exert phytopathogen biocontrol and
polymers, especially exopolysaccharides, that improve
soil structure and exoenzyme activity.
Plant growth substances
While working on the algae of Indian paddy fields, Gupta
and Lata (1964) observed that cyanobacteria accelerated
seed germination and promoted seedling growth. In
addition, they also observed that both the yield and the
quality of the grains were improved in proteins content. It
seems very likely that the beneficial effect of the algae on
the rice crop may not be restricted to their capacity to fix
atmospheric nitrogen alone, but also they have additional
beneficial roles, such as releasing of bioactive
substances. Mechanisms used by microbes to stimulate
plant growth include biofertilization (increasing the supply
of mineral nutrients to the plant), biological control
(elimination of the plant enemies including microbial
pathogens, insects and weeds) and direct plant growth
production by delivering plant growth hormones
(Lugtenberg et al., 1991). Biofertilization techniques using
cyanobacteria are recommended for increasing the rate
of seed germination and growth parameters of many
plants (Strick et al., 1997).
Although microalgae and cyanobacteria are primary
microbial photosynthetic agents of the soil, their
ecological role is still not fully defined. However, it is
obvious that some of their advantageous properties and
beneficial effects influence plant/soil-systems. Two
important potential uses of soil microalgae in crop
production are as biofertilizers or soil conditioners.
Recently, there is increasing interest in their
antimicrobial- and PGR-compounds (Plant Growth
Regulator). The effect of a great varieties of extracellular
substances production by algae including cyanobacteria,
play a valuable role in water habitats (Fogg, 1971), as
well as having a valuable role in enhancing the growth
and germination of higher plants (El-Ayouty, 1998). For
this reason, cyanobacteria algae were recommended as
a biofertilizer (Banerjee and Kumar, 1992) due to the
liberation of a very large portion of the bioactive
substances from their assimilating nitrogen outside their
cells. The previous inductions attributed to nitrogenase
and nitrate reductase activities of cyanobacteria are
associated with the surface of plants or the amino acids
and peptides produced in algal filtrate and/or other
compounds that stimulate growth of crop plants (Adam,
1999).
Microalgae are a biochemically diverse assemblage of
microorganisms amenable to formation and mass culture.
Including the cyanobacteria and nearly a dozen of
eukaryotic classes, microalgae produce a wide array of
compounds with biological activity. These may be
nitrogenous (Jones and Stewart, 1969), amino acid
(Varga et al., 1999), vitamin B12 and biotin (Misra and
Kaushik, 1989). Moreover, cyanobacteria have ability to
exude also plant growth hormones including auxins like
Abdel-Raouf et al. 11651
substances (Venkataraman, 1981), cytokinin-like
substances (Strick et al., 1997) gibberellins or gibberellic-
like substances (Shen-Rui and Shen, 1997), antibiotics,
algicide, toxins, organic acids (Hellebust, 1974) and
pharmaceutically active compounds (Metting and Pyne,
1986). A gibberellin-like substance has been isolated
from the cyanobacterium Phormidium foveolarum and
this is active in GA-bioassays (Gupta and Agarwal,
1973). Moreover, chromatography identification of an
excreted substance from Nostoc muscorum isolated from
Argentine paddy fields revealed auxinic activity and
characteristics similar to indole acetic acid (Caire et al.,
1979). Growth-promoting substances were also detected
by the effect of extracts of N. muscorum on seedlings of
Panicum miliaceum. The height of millet plants as well as
their dry weight was also increased by all the extracts
(Caire et al., 1976). Information about cyanobacterial
biomass or their substances being incorporated to other
plants different to rice is scarce (Halperin et al., 1981).
Bently (1958) in studying growth regulator production
by phytoplankton showed that some strains of Anabaena
and Oscillatoria exuded auxin-like substances. This was
confirmed by the work of Likhitkar and Tarar (1995) who
found that presoaked cotton seeds in different
concentrations of exudate of N. muscorum increased
germination rate, total length of seedlings and radicals.
Adam (1999) revealed a stimulation effect of the
cyanobacterium Nostoc muscorum on seed germination
of wheat, sorghum, maize and lentil. He also concluded
that the germination of seeds of the tested crop plants
either in live cyanobacteria inoculum algal filtrate
(exogenous) or boiled algal extract (endogenous) was
significantly increased. He attributed it to the nitrogenase
and nitrate reductase of the alga, or the amino acids and
peptides produced in the algal filtrate and/or other
compounds that stimulate growth of crop plants.
Moreover, Mahmoud and Amara (2000) revealed that
biofertilizers enhanced the growth parameters, fruit yield
as well as CO2 evolution of tomato plant. Germination and
related processes in wheat, sorghum, maize and lentil
growth parameters and contents of nitrogenous
compounds also increased. These reports indicated that
the usage of biofertilizers enhances the growth
parameters, fruit yield and vitamin C (ascorbic acid) in
tomato plants. On the other hand, Tantawy and Musa
(2001) studied the effect of cyanobacterial filtrates of
Nostoc calcicola and Anabaena flos aquae on the seed
germination and/or plant growth of some wheat, soybean
and clover crop cultivars. They found that soaking the
seeds for these crops in the filtrates of both cyano-
bacterial strains increased the germination percentage
either in the control treatment (water) and Watanabe
medium. In this respect, Aref (2001) reported that
soaking of rice seeds cultivar Sakha 102 in Nostoc sp.
live filtrate had stimulated the seed germination percent
age, reaching 90% of germination when compared to
water soaked seeds. She also showed similar stimulation
11652 Afr. J. Biotechnol.
effect with both N. muscorum and Anabaena sp. (86.8
and 83.3, respectively). Additionally, Mohamed (2001)
came to a conclusion that the treatment of rice seedlings
with the cyanobacteria filtrates of Anabaena oryzae, N.
calcicola, Microchaete tenera or Cylindrospermum
muscicola had increased both shoots and roots lengths
than those treated with water only. He owed this to the
growth promoting like-substances secreted by the
cyanobacterial strains in their filtrates.
Furthermore, Saffan and Mohamed (2001) studied the
beneficial role of some bioactive substances released by
cyanobacteria on the rate of germination Senna seeds as
well as evaluation of the metabolic changes in medicinal
plant Senna alexandrina. They reported that the exudates
of Nostoc piscinale and N. muscorum increased up the
rate of germination of Senna seeds, reaching 100 and
90% respectively after 60 h. Also, they found that the
cyanobacterial exudates contained variable concen-
trations of abscisic acid (ABA), gibberellic acid (GA3) and
indole acetic acid (IAA) and other metabolites that might
be implicated as allelochemical agents. They had also
found out a significantly increased proteins and total
soluble sugars in treatments with algal exudates,
especially those of N. piscinale and N. muscorum. The
allelopathic effects of cyanobacterial exudates (N.
muscorum, N. piscinale and Anabaena fertilissima) on
some biochemical constituents of cardon (Cynara
cardunculus) have also been studied (Saffan, 2001). The
quantitative analysis of cyanobacterial exudates revealed
the presence of phytohormones, amino acids, total
soluble nitrogen and total reducing sugars. In addition,
treatment with algal exudates stimulated the germination
rate of cardon seeds after 96 h. Furthermore, the data
revealed a significant increase in the total soluble sugar
and protein contents in germinated seeds treated with
different algae exudates.
Phytopathogen biocontrol
Application of chemical pesticides
Soil is a dynamic system in which the physical, chemical
and biotic components are in a state of equilibrium.
Application of insecticides without considering the other
soil constituents, disturb this equilibrium which adversely
affects the productivity of the soil. Maintenance of the soil
biota other than the harmful pests helps in better crop
nutrient management and maintenance of soil health.
Insecticides frequently exert inhibitory or stimulatory
effects on the growth or other activities of micro-
organisms, either in pure culture or in the field. Few
works on pesticides distributions, types, toxicity,
mechanism of actions, degradations, their tolerance by
the organisms and other physiological processes were
reviewed and summarized (Duke, 2002). Ghosh and
Saha (1988) suggested that some pesticides actually are
highly phytotoxic, such as carbaryl. The toxicity of
carbaryl was studied also by Peterson et al. (1994).
Ibraheem (2002) found that Larvin and Sevin when
applied in Egyptian soils have very toxic effects on
nitrogen fixing cyanobacteria Anabaena subtropica and
A. variabilis. Blue-green algae, especially the nitrogen-
fixers cyanobacteria, represent the major microorganisms
which contribute soil fertility. These organisms play an
important role in this system by providing a steady input
of fixed nitrogen (Roger et al., 1986) and other beneficial
roles as previously discussed (Omar, 2000). Most of the
soil and aquatic microscopic algae are sensitive to
insecticides due to the fact that algae are engaged in
photosynthesis and that many insecticides interfere with
the process.
Until now many pesticides from different chemical and
artificial sources were used as acaricidal, fungicidal and
insecticide agents (Banerjiee and Banerjiee, 1987).
These pesticides affect the distribution of fauna in their
natural ecosystems. Also, the unjustifiable and unsafe
applications of these pesticides on soils and plants cause
accumulation of different undesirable chemicals in the
crop, which may be a bigger un-direct factor in human
diseases.
Biological control
In the last decades, different researchers have studied
the replacement of chemical pesticides by natural
components of different plant and microalgal sources as
insecticide agents (Nassar et al., 1999), acaricide agents
(Amer et al., 2000; Sanchez-Ramos and Castanera,
2001; Duke, 2002) and fungicidal agents (Safonova and
Reisser, 2005, Volk and Furkert, 2006; Ibraheem and
Abdel-Raouf, 2007; Hassan, 2007). These natural
materials in addition to their lethal activities on pests,
preserves the environment of pollution, maintain the
equal distribution of fauna and also to keep the beneficial
animals. Fungi and bacteria are the main biological
agents that have been studied for the control of plant
pathogens, particularly soil-borne fungi.
Cyanobacteria have received little attention as potential
biocontrol agents of plant diseases (Hassan, 2007). Kulik
(1995) published a literature review summarizing the
potential for using cyanobacteria and algae in the
biological control of plant pathogenic bacteria and fungi.
Caire et al. (1997) reported that different concentrations
of dilute aqueous extract from nitrogen-fixing cyano-
bacterium N. muscorum Ag. were efficient in the control
of a damping-off. Also, it was found that the growth of the
plant pathogens Sclerotinia sclerotiorum and Rhizoctonia
solani, damping-off causal agents, was inhibited by
extracts from cells of N. muscorum or by extracellular
products of this cyanobacterium (Zaccaro et al., 1991).
With additional research, it should be possible to develop
thin film formulations (polymers) of bactericidal and
fungicidal cyanobacterial products that would confer
protection against soil-borne pathogens that attack seeds
and seedlings, when applied to high volume seeds and
remain competitive (Kulik, 1995). One of the modern and
advanced biotechnological researches is that conducted
on the using of different algal taxa of different habitats
(marine, fresh and soil) as a biological control for many
animal or plant diseases and also against agricultural
pests. Some of these researches studied the anti-
microbial activities against some human pathogenic
bacteria, fungi and toxic micro-algae (Noda et al., 1990).
Others were conducted on the study of toxic effects of
some algal metabolites against insects (Nassar et al.,
1999). For example, Mulla et al. (1977) found that a free
floating unicellular Chlorella elliposidea produces some
substances which affect the development and immature
stages of mosquitoes. Similar results were obtained by
Nassar et al. (1999) who found that some cyanobacteria
and green algae produce substances that inhibited larval
development and delayed the survival and development
of the adult female of mosquitoes. Van-Der Westhwzen
and Eloff (1983) noticed that toxicity of Microcystis
aeruginosa against the larvae of Culex pipiens increased
gradually during the first days of exponential phase to the
maximum and then gradually decreased at the beginning
of the stationary phase.
Further studies by other workers were conducted on
the possibility of prevention of carcinogenesis by some
algal products (Mokady and Ben-Amotz, 1991). There is
much evidence that the production of extracellular
substances by blue-green algae is widespread and
sometimes quantitatively important (Fogg, 1970). The
enhanced research activity on the subject of biological
control is in line with increased effort and determination
by microbiologists to adapt to the conceptual scheme of
integrated pest management as an acceptable eco-
system approach to disease control and to realize that
biological control must become one of the basic
components in pest management practices (Hassan,
2007).
Exopolysaccharide
Cyanobacteria produce extracellular polymers of diverse
chemical composition, especially exopolysaccharides that
enhance microbial growth and as consequence, improve
soil structure and exoenzyme activity (Ibraheem, 2007;
Hamed, 2007). Maintenance of adequate levels of soil
organic matter is essential for a sustainable and high
production of crops. Cultivation alters the structural
stability of soil and reduces the amount of N and soil
organic matter.
The nature of this labile organic matter is not fully
known, but a major portion of it could be microbial
biomass (Singh and Singh, 1995). Reducing the amount
of organic matter affects the stability of soil aggregates.
Abdel-Raouf et al. 11653
Incorporation of organic materials in soil promotes
microbial growth and enzymatic activity in the soil. Some
cyanobacteria excrete slime or mucilage that becomes
dispersed around the organism and, to an extent, partially
dissolves in the culture medium or in the soil solution.
One way to positively affect nutrient content and soil
structure is to add cyanobacteria (Rogers and Burns,
1994).
Application of algal biofertilizers is also useful for the
reclamation of marginal soils such as saline-alkali and
calcareous soils (Hedge et al., 1999). N. muscorum can
improve the aggregate stability of a saline soil, where the
increase in soil aggregation is mainly due to
exopolysaccharide secreted by microorganisms or
exopolysaccharide added to soil after death and cellular
lysis (Caire et al., 1997). Cyanobacteria can be incor-
porated into soil as organic matter and also as a source
of enzymes as they produce acid and alkaline
extracellular phosphatases that are active in solution or
located in the periplasmatic space of the cell wall. Both
biomass and exopolysaccharides incorporated into soil
induce a growth promotion of other microorganisms and
increased the activity of soil enzymes that participate in
the liberation of nutrients required by plants (Caire et al.,
2000).
TREATMENT OF HEAVY METALS
A large number of microorganisms, including cyano-
bacteria, are able to concentrate metal ions present in
their environment (Mohamed, 1994; Khalifa, 1999; Abdel-
Raouf and Ibraheem, 2001; Shaaban et al., 2004;
Samhan, 2008). Mechanisms of cyanobacterial and
microalgal resistance to heavy metals involve: 1)
environmental factors; 2) non-specific protective
mechanisms of the cell; and 3) specific protective
mechanisms developed in response to the impact of a
toxic metal species in the cell. In addition to intracellular
protective mechanisms in which the main mechanism of
biosorption of heavy metals is ion exchange in the
cyanobacterial outer cell wall, there are mucilaginous
sheaths that behave as an “external vacuole”. The metal-
binding properties are probably due to a high density of
anionic charges, especially carboxyl, identified in the
capsular polymer. This group of microorganisms could
have a higher efficiency in the biosorption during its
growth in polluted environment or in the use dried non-
living biomass for the removal of heavy metals (Gloaguen
et al., 1996).
Moreover, some of them are able to fix atmospheric
nitrogen. The use of selected diazotrophic cyanobacteria
that accumulate heavy metals would decrease the cost of
production of biomass to use as inoculum in processes of
environmental remediation. M. tenera could be used for
remediation of lead contaminated soils and waters
(Zaccaro, 2000).
11654 Afr. J. Biotechnol.
SOIL CONSOLIDATION AND DUST CONTROL
Crust formation
Soil microorganisms commonly aggregate soil particles to
form biological soil crusts, particularly in harsh environ-
ments where vascular plant distributions are patchy and
water is limited (Hawkes and Flechtner, 2002; Ibraheem,
2003; Abdel-Raouf et al., 2004). Biological crusts
consisting of algae, cyanobacteria, lichens, microfungi,
bacteria, and mosses are common in habitats where
water and nutrients are limited and vascular plant cover is
discontinuous. Crusts alter soil factors, including water
availability, nutrient content, and erosion susceptibility,
and thus are likely to directly and indirectly affect plants
(Hawkes and Flechtner, 2002; Stal, 2007; Bhatnagar et
al., 2008).
Cyanobacteria and other crust organisms stabilize the
soil by binding together small particles into larger
particles (Shields and Durrell, 1964). This binding is
achieved by several mechanisms (Bar-Or and Danin,
1989) including: physical binding of soil particles by
entangled filaments, adhesion to mucilaginous sheaths or
slime layers excreted by cyanobacterial trichomes and
attachment of particles to sites along the cyanobacterial
cell walls. This binding increases the organic matter
content of the crust (Danin et al., 1989), improving soil’s
resistance to both wind and water erosion. The
importance of micro-organisms for enhancing the stability
of soil aggregates is well recognized (Eldridge and Leys,
2003). Bailey et al. (1973) demonstrated enhanced
aggregation when soils were inoculated with algae or
cyanobacteria. Cyanobacteria and microphytes exude
gelatinous materials that adhere or entangle clay
particles in sand, and this process concentrates the
microorganisms at the soil surface. The crusts are formed
by the entanglement of cyanobacteria and algae fila-
ments, lichen and moss thalli and soil particles (Chartres,
1992). Polysaccharides excreted by filamentous algae
and cyanobacteria, along with the living organisms
themselves, bind soil particles together into a single,
consolidated layer to form a crust of the first few
centimeters of surface soil (Campbell et al., 1989). The
importance of soil crust development in ecological
functioning in arid and semi-arid regions is well
established (Harper and Marble 1998). In the arid desert
regions of China, soil crusts are common once the
shifting sand dunes have been stabilized.
Microbiotic crust communities occur throughout arid
and semi-arid regions of the world, and an interest in their
role in nutrient cycling and the discovery of a rich
microfauna and microflora have led to a growing number
of ecological, physiological and taxonomic studies (Lewis
and Flechtner, 2002). The earliest surveys of microbiotic
crust organisms to include algae began in the 1960s with
Cameron (1960, 1964), Shields and Drouet (1962) and
Friedmann et al. (1967). These studies revealed a very
small number of green algae from a given site. It is
important to characterize the spatial distributions of
organisms within crusts because of their biotic effects on
both physical and chemical soil properties and their
potential influence on vascular plants. A variety of biotic
and abiotic factors may contribute to spatial heterogeneity
of crust organisms (Hawkes and Flechtner, 2002).
Stabilization of soil aggregate
Mucilaginous (palmelloid) green microalgae are as soil-
conditioning agents on a very small scale in the United
States (Shujinš, 1991). Soil conditioning is any procedure
or product that improves not only the physical properties
of soil for agriculture, but also the soil structure by
genesis and/or stabilization of soil aggregates. Aggregate
formation is complex and poorly understood. However,
aggregate stabilization is known to be primarily due to
adsorption and binding of particulates by polysaccharides
or microbial origin together with environment by living
microbial filaments (Burns and Davies, 1986). When
inoculated on to irrigated sandy soils through center pivot
sprinklers, mass-cultured Chlamydomonas and
Asterococcus species (Chlorophyceae) have been shown
to significantly improve the integrity of soil aggregates in
the face of disruption by wind and slaking in water
(Hawkes and Flechlner, 2002).
AGRICULTURAL WASTEWATER TREATMENT
Pollution of agricultural water drains is a man-made
phenomenon, arising either when the concentrations of
naturally occurring substances are increased or when
non-natural synthetic compounds (xenobiotics) are
released into the environment. Organic substances
released into the environment as a result of domestic,
agricultural and industrial activities leads to an inorganic
pollution (Mouchet, 1986). There are still a number of
cases where municipal and rural domestic wastewater is
discharged directly into waterways, often without
treatment. These discharges are increasing year after
year due to the existing plan for water supply networks
set-up in many villages. Also, the present expansion of
water networks in several towns without parallel
construction of new sewerage systems or rehabilitation of
the existing ones aggravate the problems and lead to
pollution problems of the water bodies and increasing
public health hazards. The constituents of domestic and
urban input to water resources are pathogens, nutrients,
suspended solids, salts and oxygen demanding materials
(Singh and Dhar, 2006).
The agricultural drains sometimes receive the bulk of
the treated and untreated domestic pollution load (Abdel-
Raouf et al., 2004). As a result, many canals now also
are contaminated with wastewater pollutants. Apart from
being the largest consumer of water, agriculture is also a
major water pollutant. Saline irrigation return-flows or
drainage containing agrochemical residues are serious
contaminants for downstream water users. Moreover,
agricultural nitrate contaminates groundwater. The
disposal of liquid animal waste pollutes surface and
groundwater, etc. This means a large number of organic
and inorganic substances disturb the water quality, which
is the main cause of eutrophication of water body. They
also proved to be powerful stimulants to algal growth and
consequently formation of "algal blooms". An algal bloom
can affect the water quality in several ways.
Many investigations have been conducted and
concerning the distribution and species composition of
fresh water algal communities in different water supplies
in Egypt in response to the impact of some environmental
stresses (Abdel-Raouf et al., 2004). The polluted rivers,
lakes and seas, were aesthetically displeasing also by
man, which importantly were a public health hazard,
since they harbored human pathogens and increased the
risk of spreading excreta-related diseases through the
water-borne route. In order to prevent such problems, the
sewage treatment systems were designed. Through most
of human history, agriculture has been in effect a major
form of biological water treatments through its use of the
potential pollutants of human and animal wastes to
support plant growth. Municipal sewage, for example
sometimes after treatment is applied as a source of
nutrients over land occupied by natural vegetation or
various crops (Wood-Well, 1977). Such wastes are still
important in world agriculture, especially where
commercial fertilizers are not readily available (Tourbier
and Pierson, 1979).
The history of the commercial use of algal cultures
spans about 55 years with application to wastewater
treatment and mass production of different strains such
as Chlorella and Dunaliella. Currently, significant interest
is developed in some advanced world nations such as
Australia, USA, Thailand, Taiwan and Mexico (Renaud et
al., 1994). These are due to the understanding of the
biologists in these nations for the biology and ecology of
large-scale algal cultures, as well as in the engineering of
large-scale culture systems and algal harvesting
methods, all of which are important to the design and
operation of high rate algal cultures to produce high-value
products, such as Pharmaceuticals and genetically
engineered products (Javanmardian and Palsson, 1991).
These include antibacterial, antiviral, antitumor/anti-
cancer, antihistamine, antihyperlipidemic and many other
biologically valuable products (Abdel-Raouf and
Ibraheem, 2008; Abdel-Raouf et al., 2011).
Some industrial and agricultural wastewaters show total
nitrogen and phosphorus concentrations up to three
orders of magnitude higher than natural water bodies (de
la Noüe et al., 1992). The normal primary and secondary
treatment processes have been introduced in a growing
number of places, in order to eliminate the easily settled
materials (primary treatment) and to oxidize the organic
Abdel-Raouf et al. 11655
material present in wastewater (secondary treatment).
The final result is a clear, apparently clean effluent which
is discharged into natural water bodies. This secondary
effluent is, however, loaded with inorganic nitrogen and
phosphorus and causes eutrophication and more long-
term problems because of refractory organics and heavy
metals that are discharged.
Tertiary treatment process removes all organic ions. It
can be accomplished biologically or chemically. The
biological tertiary treatment appears to perform well
compared to the chemical processes which are in general
too costly to be implemented in most places and may
lead to secondary pollution. However, each additional
treatment step in a wastewater system greatly increases
the total cost; the relative cost of treatment doubles for
each additional step following primary treatment (Oswald,
1988a). A complete treatment of wastewater from
different sources process aimed at removing ammonia,
nitrate and phosphate (Oswald, 1988a). Microalgal
cultures offer an elegant solution to tertiary and quinary
treatments due to the ability of microalgae to use
inorganic nitrogen and phosphorus for their growth
(Oswald, 1988a, b; Tam and Wong, 1995) and also for
their capacity to remove heavy metals (Hammouda et al.,
1995), as well as some toxic organic compounds
(Redalje et al., 1989). Therefore, it does not lead to
secondary pollution. Amongst beneficial characteristics,
they produce oxygen and have a disinfecting effect due
to increase in pH during photosynthesis (de la Noüe and
De Pauw, 1988).
CONCLUSION
In this review, an attempt was carried to throw some light
on the different beneficial roles of algae in agriculture,
with regard to the relationship between algae and crop
plants. Algae are important components of arid and semi-
arid ecosystems. Furthermore, their distribution may
indicate the health of the environment. In recent years,
much considerations were sent towards the possibility of
using algae as biological conditioners instead of any
artificial or chemical conditioners, where algal use
reduces the resultant pollution to soil and plants together,
in addition to their ability to improve both soil and plant
properties.
Algae, especially microalgae and cyanobacteria are
ubiquitous in the world soils. Although they are the
primary microbial photosynthetic agents of the soil, their
ecological role is still not fully defined. In this study,
emphasis was laid on the role of algae, especially
microalgae in soil fertility and reclamation and some of
their advantageous properties and beneficial effects
influence the plant/soil system, such as:
(1) Excretion of organic acids that increase P-availability
and P-uptake,
11656 Afr. J. Biotechnol.
(2) Provision of nitrogen by biological nitrogen fixation,
(3) Increased soil organic matter,
(4) Production and release of bioactive extracellular
substances that may influence plant growth and
development. These have been reported to be plant
growth regulators (PGRs), vitamins, amino acids,
polypeptides, antibacterial or antifungal substances that
exert phytopathogen biocontrol and polymers, especially
exopolysaccharides, that improve soil structure and
exoenzyme activity.
(5) Crust formation
(6) Stabilization soil aggregation by extracellular
polysaccharides of soil aggregate
(6) Concentrate metal ions present in their environment.
This review also reinforced the role of algae in the
treatment and agricultural recycling of wastewater. A
complete treatment of wastewater from different sources
process aims at removing ammonia, nitrate, phosphate
and some heavy metals.
ACKNOWLEDGEMENT
The article was supported by the Research Center,
College of Science, King Saud University.
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... These conditions constrain the research area for this thesis to gently to moderately sloped agricultural landscapes which are intensively managed. These undulating landscapes are numerous around the globe, but occur most often in glacial till-or loess-based settings, due to the high fertility of the parent material (Catt, 2001;Bedard-Haughn and Pennock, 2002;Zhang et al., 2004;Vitharana et al., 2008;Kumar et al., 2018;Wilson et al., 2018). ...
... For our simulations, we created a hypothetical loess-covered, hilly landscape with a range of characteristic slope positions as spatial setting. We choose loess, because it is a relatively homogeneous parent material, widely spread globally and favored for agricultural practices due to its high water holding capacity and resulting fertility (Catt, 2001). The long-term use of loess areas for agriculture and unsustainable management has resulted in severe land degradation (e.g. ...
Thesis
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Soils provide numerous functions to support natural and human life. Soils and their functions develop over long timescales (decennia to millennia) under influence of environmental properties and drivers such as water flow, vegetation type and topography of the landscape. At the same time, these environmental properties develop too, often under influence of soil properties and processes. This interactive co-evolution of soils and the landscape forms a complex system that can aggravate, or diminish, rates and direction of soil-landscape evolution. In the Anthropocene, a proposed geological Epoch where humans are the main forcing actors, soil-landscape evolution changed substantially under influence of anthropogenic processes, such as deforestation and tillage. In current intensively managed agricultural landscapes in undulating settings, rates of anthropogenic erosion far exceed rates of natural soil development, leading to severe soil and land degradation. Sustainable nature-based land management is crucial to counteract this degradation, and to preserve and restore soil functions for the environment and future generations. The aim of my thesis is to identify and quantify how soils and landscape have evolved and possibly co-evolved during the transition from natural land cover to intensive land management in the Anthropocene. The first part of this thesis (Chapter 2-3) aims at reconstructing the impact and rates of anthropogenic landscape change on complex agricultural fields. As study site I use the landscape laboratory CarboZALF D. CarboZALF D is a kettle-hole catchment of 4 ha with elevation differences up to 8 meters, located in north-eastern Germany. The catchment is characterized by complex small-scale topography, heterogeneities in the hydrological system and a long history of agricultural use. The colluvium in the closed kettle hole catchment provides a complete geo-archive of landscape change. In Chapter 2 we reconstruct the paleosurface of study site Carbo-ZALF-D prior to the anthropogenic erosion. We used an extensive dataset of soil descriptions, which enabled a detailed spatial estimate of erosion and deposition by estimating erosion based on soil profile truncations and deposition based on colluvium thickness. The paleosurface shows a high variation in topographic properties and suggests that natural soils and landscapes contain considerable spatial heterogeneity. In Chapter 3 we reconstruct the rates of deposition in Carbo-ZALF-D using Optically Stimulated Luminescence (OSL) dating. We present a novel methodology to apply OSL dating in colluvial sediments, where the soil chronology gets disturbed by reworking by ploughing after deposition. Our results show a 100-fold increase in deposition rates, starting around 5000 years ago. This increase does not solely represent increased erosion in the catchment, but is also caused by indirect effects of agricultural drainage. The kettle hole shows a complex spatiotemporal pattern of colluvial infilling and landscape evolution, which we were only able to reconstruct using a high OSL sampling density and extensive soil geomorphic research. The second part of this thesis aims at simulating the evolution of soils and landscapes under varying climatic and anthropogenic forcing. In Chapter 4 we review the role of water as dominant driver in natural soil and landscape evolution and its potential as driver in simulations with soil-landscape evolution models (SLEMs). Water plays a pivotal role in soil and landscape evolution, by transporting and transforming soil material and facilitating vegetation growth. In turn, surface and subsurface flow paths of water are controlled by soil and landscape properties. The co-evolution of soils, topography and the hydrological system is essential for understanding the response of soils and landscapes to changes in climate. However, this co-evolution can currently not be simulated over long timescales with SLEMs due to several conceptual and methodological challenges. We provide partial solutions for these challenges. In Chapter 5 we utilize these partial solutions to develop our SLEM HydroLorica. HydroLorica simulates soil and landscape evolution with various dynamic drivers such as water flow, vegetation type and land use. We included additional essential processes such as tree throw, soil creep and tillage. We use HydroLorica to simulate the evolution of soils and landscape under various rainfall and land-use scenarios for an artificial undulating landscape. The results show that in natural systems, rainfall amount is the dominant factor controlling soil and landscape heterogeneity, while for agricultural systems landform explains most of the variation. The cultivation of natural landscapes increases soil heterogeneity, but also increases correlations between soil and terrain properties. Our results confirm that humans have become the dominant soil forming factor in intensively managed landscapes. In the third part of this thesis (Chapter 6), I synthesize the findings from the research chapters to meet the objectives of this thesis. I critically evaluate the developed reconstruction methods in Chapters 2 and 3 and compare them with other potential methods. The development of HydroLorica in Chapters 4 and 5, with water flow as explicit driver and with increased process coverage, is a big step forward in soil-landscape evolution modelling. A combination of reconstruction and simulation methods is essential for developing and testing hypotheses of soil-landscape co-evolution. Soil-landscape evolution in natural and intensively managed landscapes have different characteristics due to different driving forces and dominant processes. In natural landscapes, soils develop to patterns where individual soils might be disturbed occasionally, but where the average properties are stable. In intensively managed landscapes, disturbance rates are much higher than in natural settings. As a consequence, slowly developing soil properties degrade, while fast-developing soil properties can form a new equilibrium. The co-evolution of soils and landscapes that occurs in natural settings is often controlled by biotic processes. In agricultural settings, humans control vegetation type and aggravate erosion processes through tillage. As a consequence, co-evolution does not occur in the sense that it does in natural settings, because interactions between landscape components are missing. However, the management of soils and landscapes is often adapted to counteract unintended changes to soils and landscapes under earlier management. In intensively managed landscapes, land management may thus co-evolve with the rest of the landscape.
... Marine algae are demonstrated as crucial fertilizers, resulting in less nitrogen and phosphorus runoff than the one from the use of livestock manure [17]. Several researches revealed the effect of marine algae on seed germination and root development, frost resistance, nutrient uptake, increased resistance to pathogenic fungi, reduced incidence if insect attack, restauration and stimulation of plant growth under saline or non-saline soil, respectively [4,18]. ...
... These substrates widely differ in their textural composition and nutrient supply. For example, sandy sedimentary materials can be expected to have substantially smaller nutrient contents than basaltic, more phyllosilicate rich rocks or soils developed from silt-and nutrient-rich Loess deposits (Anderson, 1988;Catt, 2001). These differences likely do not only influence the SOC preservation capacity of a soil (Hassink, 1997) but also litter production (and thus input of OM or contribution of root as compared to shoot-derived OM; Crow et al., 2009;Kögel-Knabner, 2002) via different levels of soil nutrients, such as phosphorus (Wright et al., 2011). ...
Article
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Despite a large body of studies investigating soil organic carbon (SOC) stocks and potential influencing factors, the impact of contrasting parent material, particularly in the subsoil, has received little attention. To reveal potential effects varying parent materials exert on SOC stocks, we investigated chemical (⁠14C content and overall chemical composition via ⁠13C NMR spectroscopy) and plant/microbial related parameters (root mass, amino sugars) of bulk soil and soil organic matter fractions from topsoil, subsoil, and rhizosphere soil at three European beech stands (Fagus sylvatica L.) only differing in parent material (Tertiary sand, Quaternary loess, and Tertiary basalt). The results suggest that the clay fraction, its amount being largely dependent on the respective parent material, took a central role in shaping differences in SOC stocks among the investigated sites by affecting soil organic matter stabilization via organo-mineral association and aggregation. This fraction was particularly relevant in the subsoil, where it accounted for up to 80% of the bulk soil SOC stocks that decreased with decreasing amounts of the clay fraction (basalt>loess>sand site). Determining the soil's nutrient composition, parent material likely also indirectly affected SOC stocks by changing rhizosphere traits (such as fine root density or mortality) and by attracting root growth (and thus organic matter inputs) to subsoil with higher nutrient contents, where in situ root inputs in the form of rhizodeposits were likely the prime source of plant-derived SOC. However, root inputs also contributed in large part to topsoil SOC stocks and were associated with higher abundance of microbial compounds (amino sugars), whose relative importance increased with increasing soil depth. Independent of soil depth and site, amino sugars and the amount of the clay fraction, combined with parameters related to the input of organic matter (root mass and amount of the particulate organic matter fraction) explained more than 90% of the variability in SOC stocks, indicating a key role of these measures in impacting SOC stocks. Because parent material directly or indirectly influenced these parameters, we demonstrate the necessity to consider differences in parent material when estimating and predicting SOC stocks.
... Some algae strains favour high biomass production and other high lipid concentration (Yoo et al. 2010). Biomass of microalgae in agriculture can be used also as bio fertilizer and as soil conditioner (Faheed & Fattah 2008;Mata et al. 2010;Coppens et al. 2015;Uysal et al. 2015;Abdel-Raouf et al. 2016;Renuka et al. 2016). Additionally, the role of blue-green algae in supplying N for rice growing and for improving physico-chemical properties of soil is well documented (Metting 1996;Mandal et al. 1999;Song et al. 2005). ...
Article
Soil structure is a key determinant of many soil environmental processes and is essential for supporting terrestrial ecosystem productivity. Management of arable soils plays a significant role in forming and maintaining their structure. Between 1994 and 2011, we studied the influence of soil tillage and fertilisation regimes on the stability of soil structure of loamy Haplic Luvisol in a replicated long-term field experiment in the Dolná Malanta locality (Slovakia). Soil samples were repeatedly collected from plots exposed to the following treatments: conventional tillage (CT) and minimum tillage (MT) combined with conventional (NPK) and crop residue-enhanced fertilisation (CR+NPK). MT resulted in an increase of critical soil organic matter content (St) by 7% in comparison with CT. Addition of crop residues and NPK fertilisers significantly increased St values (by 7%) in comparison with NPK-only treatments. Soil tillage and fertilisation did not have any significant impact on other parameters of soil structure such as dry sieving mean weight diameters (MWD), mean weight diameter of water-stable aggregates (MWD<sub>WSA</sub>), vulnerability coefficient (Kv), stability index of water-stable aggregates (Sw), index of crusting (Ic), contents of water-stable macro- (WSA<sub>ma</sub>) and micro-aggregates (WSA<sub>mi</sub>). Ic was correlated with organic matter content in all combinations of treatments. Surprisingly, humus quality did not interact with soil management practices to affect soil structure parameters. Higher sums of base cations, CEC and base saturation (Bs) were linked to higher Sw values, however higher values of hydrolytic acidity (Ha) resulted in lower aggregate stability in CT treatments. Higher content of K<sup>+</sup> was responsible for higher values of MWD<sub>WSA </sub>and MWD in CT. In MT, contents of Ca<sup>2+</sup>, Mg<sup>2+ </sup>and Na<sup>+</sup> were significantly correlated with contents of WSA<sub>mi </sub>and WSA<sub>ma</sub>. Higher contents of Na<sup>+</sup> negatively affected St values and positive correlations were detected between Ca<sup>2+</sup>, Mg<sup>2+ </sup>and Na<sup>+</sup> and Ic in NPK treatments.
... Regarding the results of this study, we believe that biological fertilizers or any other biological agent can be used as environmentally-friendly and even costeffective (Kavalekar, 2013), they not only increase agricultural production but also reduce environmental pollutions. Biological fertilizers are products that involve living natural compounds derived from organisms such as bacteria, fungi and algae that improve soil chemical and biological properties, stimulate plant growth, and restore soil fertility (Abdel-Raouf et al., 2012). Results showed significant differences between the bio-fertilizer treatments. ...
Article
Full-text available
The results obtained indicate a favorable climate change for cereal yields. This change in climate was expressed by increase in maximum temperature of 1.45°C, minimum temperature of 1.26°C and 2.5 mm increase in precipitation. It was also observed that change in climate increased the total production of wheat to 16544.4 tonnes during the studied periods of 1990 to 2004 and 2004 to 2014 due to improved productivity of wheat to 6.33 tonnes/ha. It was also observed that different durum wheat producing regions in eastern Algeria did not differ significantly in respect to production. On the basis of this study, it can be concluded that climate change had positive effect on durum wheat production in the Bordj Bou Arréridj province of Algeria.
... They are unique photosynthetic organisms with extra ordinary potential. Algae find diverse application in agriculture (1). There are numerous advantages associated with algae as enlisted in the flowing table : ...
Article
Full-text available
Sustainable agriculture aims at enhancing agricultural production by adopting environmental friendly technology. Algaeare diverse group of unique organism possessing myriad of potentials. They are photosynthetic microbesinhabiting plethora of habitats.Algae are pioneers of the biological transformation of solar energy and nutrientsfrom the waste to the biomass of algae, which can undergo anaerobic fermentation giving methane(approximately 60%) and of Carbon dioxide (about 40%), which in turn can be returned to cultivation of algae asa source of carbon. They have been exploited in agriculture since decades as biofertilizers, soil stablisers and plant growth promoters.Algae production could be more ecofriendly and efficient by closing production cycles, whereagricultural wastes and animal wastes are used as a medium for the growth of algae. The biomass generated byvirtue of remediation of waste water or utilization of nutrients not consumed by animals can be exploited forbiofuels and nutraceuticals. The use of molecular techniques can also enhanced our capacity to understand andmanage the algae-crop interaction and this will lead to new products with improved effectiveness and efficiency.Genetic enhancement of algal strains with improved effectiveness may involve addition of one or more traitsassociated with plant growth promotion. Algal biofertilizers can provide a suitable support to agriculture byreducing use of chemical fertilizers, and ‘organic farming’ can become a reality in the future by exploring theunique potential of algae.
... Concerning green seaweed elemental composition, in general, levels of calcium (Ca), potassium (K), sodium (Na), and magnesium (Mg) are high, exceeding contents in other seaweed groups except for K, which is much more abundant in some studied brown seaweeds (Makkar et al., 2015). Nonetheless, green seaweeds may be used as organic fertilizers just as brown seaweeds (Abdel-Raouf, Al-Homaidan, & Ibraheem, 2012), owing to their appreciable K content. Other authors have shown that green seaweeds are also a relatively rich source of iron (Fe) (Yaich https://doi.org/10.1016(Yaich ...
Article
The elemental composition of five species of green seaweeds (Chaetomorpha linum, Rhizoclonium riparium, Ulva intestinalis, Ulva lactuca, Ulva prolifera) grown in fish pond aquaculture systems were studied. The elemental bioaccessibility in these species was also investigated through the application of an innovative in vitro digestive model of the human gastrointestinal tract. It was observed that R. riparium had the highest levels of Mn, Sr, Cd, Sn, and I and that U. lactuca had the highest Ni and Cu concentrations. The daily amounts of dried green seaweed required for achieving specific dietary intakes were calculated, namely: 7 g of dried U. lactuca (for meeting Cu Recommended Daily Allowance, RDA); 173 g of dried U. lactuca (Zn RDA); 78 g of dried C. linum (Se RDA); 41 g of dried C. linum (Mo RDA); and 0.5 g of dried R. riparium (I Dietary Reference Intake, DRI). Concerning elemental bioaccessibility, Mn and Cu had the highest values, always above 50%, I values were in the lower range, between 14 and 31%. The elemental bioaccessibility range of R. riparium (31–100%) was higher than the ranges for other species, particularly C. linum (0–56%). The bioaccessibility results entailed higher quantities of dried seaweed for reaching dietary intakes: 10 g of dried U. lactuca (Cu RDA); 290 g of dried R. riparium (Zn RDA); and 2 g of dried R. riparium (I DRI). Accordingly, R. riparium is a very rich I source. This study showed the importance of taking into account bioaccessibility results in estimating dietary intakes.
... During the last decades, the algal bio-fertilizers technology has been proven to be a highly applicable and a key player instead of inorganic chemical fertilizers ( Maqubela et al., 2009). Furthermore, this technique is commonly avoiding soil pollution by adding chemical fertilizers affecting human health ( Abdel-Raouf et al., 2012), improves the nutrients-poor soils specifically those important for seedlings germination and crops productivity ( Gheda & Ahmed, 2015) and they continuously fix atmospheric nitrogen into the soil even after crop harvest ( Sahu et al., 2012). The main scope of this work is to unearth and identify species composition of soil algal assemblages in El-Farafra Oasis, as well as evaluation of N 2-fixation efficiency of certain isolated heterocytous cyanophytes. ...
Article
Full-text available
In total 47 soil algal morphospecies were cultured and identified from the desert soils of El-Farafra Oasis, the Western Desert (Egypt). The most of them were related to Cyanophyta (34 algal taxa), followed by Chlorophyta and Xanthophyta (5 algal taxa belonging to each). Bacillariophyta was represented only by 3 species. Moreover, this work enriched the Egyptian soil algal flora with 5 different algal taxa: Westiellopsis prolifica Janet, Cylindrospermum gregarium (Zakrz.), Cylindrospermum. licheniforme (Bory) Kütz., Chlorocloster caudatus Pasch. and Tetraktis aktinastroides Pasch. Furthermore, the potentialities of atmospheric N2-fixation efficiency of Calothrix elenkinii Kossinsk., Nodularia harveyana f. sphaerocarpa (Born. et Flah.) Elenk., Scytonema ocellatum Lyngb., Stratonostoc linckia (Roth) Elenk., and Westiellopsis prolifica Janet were investigated. C. elenkinii, W. prolifica and S. ocellatum exhibited to a large extent the highest fixation rates with mean values of 18.89, 30.52 and 33.01 μmole ml-1 h-1, respectively, followed by S. linckia (16.71 μmole ml-1 h-1) and Nodularia harveyana f. sphaerocarpa (12.01 μmole ml-1 h-1). In conclusion, S. ocellatum and W. prolifica can used as promising ecofriendly natural bio-fertilizers for the sustainable development in the Egyptian desert habitat.
... During the last decades, the algal bio-fertilizers technology has been proven to be a highly applicable and a key player instead of inorganic chemical fertilizers ( Maqubela et al., 2009). Furthermore, this technique is commonly avoiding soil pollution by adding chemical fertilizers affecting human health ( Abdel-Raouf et al., 2012), improves the nutrients-poor soils specifically those important for seedlings germination and crops productivity ( Gheda & Ahmed, 2015) and they continuously fix atmospheric nitrogen into the soil even after crop harvest ( Sahu et al., 2012). The main scope of this work is to unearth and identify species composition of soil algal assemblages in El-Farafra Oasis, as well as evaluation of N 2-fixation efficiency of certain isolated heterocytous cyanophytes. ...
Chapter
Microalgal biofuels are environmentally friendly fuels regarded as a potential alternative to fossil fuels. Algae are fast-growing photosynthetic microscopic plants compared with terrestrial ones. Microalgae exhibit an inherent potential to accumulate various metabolites inside a cell, which can be utilised for various industrial applications. Cultivation of microalgae for biofuel and high-value chemical applications is costly due to the consumption of substantial freshwater nutrients, such as nitrogen and phosphorous. Mass production of algal biomass in freshwaters is an impractical approach due to increasing demands in the future. Multi-application of microalgae for wastewater treatment for low-cost biomass for biofuel and high-value chemicals and bioremediation can be a viable alternative to various stipulations, such as lowering cost of nutrients, freshwater resources and energy. This chapter discusses the various types of wastewater remediation and industrial-scale bioreactors for biofuel production and wastewater remediation by microalgae Chlorella sp., respectively. In addition, the life cycle assessment of bioremediation and its future perspectives are analysed.
Article
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The present investigation evaluated the effectiveness of Dunaliella sp. and Aphanocapsa elachista cells in concentrating copper and nickel in their cells and thereby removing the two metals from solution. Dunaliella sp. (unicellular green alga) was isolated from the 1 st kilometer of Wadi-Sannur (moisted soil with underground water) at the 10 th Kilometer, Eastern-South desert of Beni-Suef Governorate. On the other hand Aphanocapsa elachista (blue-green alga) was isolated from polluted agricultural stream receiving domestic wastewater from Wastewater Treatment Station (WWTS) at Beni-Suef City. The two different taxa were subjected to different concentrations of copper and nickel respectively. It was revealed that Dunaliella sp. was the most tolerant species to copper and nickel since the growth of such alga was not affected at higher concentrations of both elements. The highest concentration of the tested substance that does not inhibit growth rate of the alga was demonstrated by copper 10 and nickel 20 ppm. On the other hand Aphanocapsa elachista had the lowest tolerance to the two metals (copper 2 and nickel 5 ppm). It was further revealed that Dunaliella sp. had higher concentration factor and removal efficiency of nickel (7753 mg L-1 & 78%) and higher concentration factor and removal efficiency of copper (8375 mg L-1 & 68%) when exposed to maximum concentration of nickel (20 ppm) and copper (10 ppm).
Article
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Ten cyanobacterial species (Nostoc calcicola , N. commune, N. entophytum, N. minutum, N. palndosum, N. passerianum, N. punctiforme, Anabaena ambigua, A. amomala, and A. doliolum) were isolated from the mangrove region of Ras Mohammed (Sinai, Egypt) and have been tested for their allelopathic activity that of inhibitory and / or promoting effects against two Gram positive bacteria (Bacillus subtilis and Staphylococcus aureus) and two Gram negative bacteria (Escherichia coli and Pseudomonas aeruginosa). Data suggested two types of allelopathic effects: one type which always appeared in cyanobacterial medium as in the case with Nostoc minutum (medium that inhibits the growth of all tested bacterial species). The other type is induced only when Cyanobacteria are in contact with bacteria; this is the case when the growth of both Bacillus subtilis and Staphylococcus aureus were inhibited in co-culture with Nostoc commune. On the other hand, promotion effects of bacterial growth were observed when grown in cyanobacterial metabolites in most of studied cyanobacterial species. The biological assays for aqueous and methanolic extracts of the two Nostoc species revealed that both extracts for each species were not toxic at concentrations of 0.52 and 0.59 g L-1 water extract for Nostoc commune and N. minutum, respectively and 0.31 and 0.425 g L-1 for methanolic extract for Nostoc commune and N. minutum, respectively. No mortality was observed in tested mice within 72 hours
Article
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Microalgal crusts of 12 desert plant communities distributed in 3 different stands in Wadi Araba and its tributaries (Eastern Desert, Egypt) were involved in the present investigation. Four sites were selected in each stand. Soil crusts and samples were collected during March 2003, and some physico-chemical characters of these samples in addition to some biotic and abiotic factors were determined. A total of 92 algal species were recorded in all sites. Of these, 48 species belong to Cyanophyta, 20 to Chlorophyta and 24 to Bacillariophyta. The data revealed that the quantity and quality of microbiological algal crusts were governed by the type of the flowering plants as well as by the edaphic factors and physico-chemical characters of the soil.
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