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Soil biological health - what is it and how can we improve it?


Abstract and Figures

SOIL BIOLOGICAL HEALTH is a topic of great interest to sugarcane growers, although there is confusion as to what constitutes soil health. Many growers and consultants are unaware that beneficial organisms, rather than pathogens and pests, dominate the biological community in a healthy soil. Considering the vast diversity of soil organisms and their complex interactions, it is unsurprising that there is limited knowledge about how farming practices precisely impact on soil biological health, and how biological health can be achieved. The former Sugar Yield Decline Joint Venture (SYDJV) and subsequent activities have demonstrated that soil biological health represents a significant production constraint. The modern farming system (MFS), with controlled traffic, permanent beds, minimum tillage, legume break crops and crop residue retention, aims to overcome soil constraints, including soil biological health, by minimising problems arising from soil compaction, continuous monoculture and low levels of soil organic matter. In this paper we discuss key organisms that inhabit soils under sugarcane production and how soil biology responds to management practices. We highlight biological indicators of soil health, and their usefulness to growers for quantifying soil responses to changed farming practices. We outline research needs to advance the industry’s ability to manipulate soil biological health.
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Brackin R et al. Proc Aust Soc Sugar Cane Technol Vol 39 2017
1The University of Queensland, Brisbane, 2The University of the Sunshine Coast, Sippy Downs,
3Sugar Research Australia, Woodford
KEYWORDS: Soil Food Web, Organic Matter,
Soil Health Indicators, Soil Biology.
SOIL BIOLOGICAL HEALTH is a topic of great interest to sugarcane growers, although
there is confusion as to what constitutes soil health. Many growers and consultants are
unaware that beneficial organisms, rather than pathogens and pests, dominate the
biological community in a healthy soil. Considering the vast diversity of soil organisms
and their complex interactions, it is unsurprising that there is limited knowledge about
how farming practices precisely impact on soil biological health, and how biological
health can be achieved. The former Sugar Yield Decline Joint Venture (SYDJV) and
subsequent activities have demonstrated that soil biological health represents a
significant production constraint. The modern farming system (MFS), with controlled
traffic, permanent beds, minimum tillage, legume break crops and crop residue
retention, aims to overcome soil constraints, including soil biological health, by
minimising problems arising from soil compaction, continuous monoculture and low
levels of soil organic matter. In this paper we discuss key organisms that inhabit soils
under sugarcane production and how soil biology responds to management practices.
We highlight biological indicators of soil health, and their usefulness to growers for
quantifying soil responses to changed farming practices. We outline research needs to
advance the industry’s ability to manipulate soil biological health.
The physical and chemical components of soil quality are well understood, and
quantification methods exist that are accessible to growers and consultants (Stirling et al. 2016).
Soil biological traits and their relationships with crops are more complex, and there are large
deficiencies in fundamental knowledge (Lehman et al., 2015).
Only about 100 000 species of soil fungi are known of an estimated 5 million species, and
4 500 identified species of soil bacteria contrast an estimated 1 billion species inhabiting soils
(Nielsen et al., 2016). Such knowledge gaps hinder the development of robust tools for
practitioners, and understanding of soil biological traits at the paddock scale is in its infancy.
Soil contains a vast diversity of organisms, with differing functions, requirements and life
cycles, and in which uncountable numbers of individual organisms exist and interact.
The diagram (Figure 1) shows the diverse sizes of the soil community across many orders of
magnitude from microscopic bacteria (~1 µm and below) to larger organisms such as earthworms,
which are several centimetres in length.
As a whole, the soil biological community provides a number of essential ecosystem
services, particularly decomposition of organic matter and release of nutrients for plant uptake, soil
formation, storage and recycling of nutrients, growth promotion and suppression of pests and
diseases, and the degradation of toxins (Table 1) (Stirling 2014).
Brackin R et al. Proc Aust Soc Sugar Cane Technol Vol 39 2017
Fig. 1Soil organisms grouped by class, showing the size of body width. Bacteria in the
diagram represent all prokaryotes, bacteria and Archaea.
Despite their small size (when considering individual bacteria or fungal hyphae), soil
microbes strongly influence soil structure (Ritz and Young, 2004) and are instrumental for the
build-up of soil organic matter (Fontaine and Barot, 2005). Specific groups of microbes are
responsible for more specialised functions, including the conversion of atmospheric nitrogen into
reactive nitrogen that crops can use (biological nitrogen fixation), nitrification, and suppression of
pathogens (Stirling et al., 2016). Certain organism groups are responsible for negative soil
biological function including crop diseases.
In general, soil microbes are limited by energy (not nutrients) and most of their activities are
centred around obtaining energy, either through consuming organic material, oxidising inorganic
substrates (i.e. nitrification), or taking energy directly from living plants (which are often energy
rich but nutrient limited) (Brackin et al., 2014; Hobbie and Hobbie, 2013). This can occur through
negative interactions such as pathogenicity or predation, but also via co-operative interactions
where microbes ‘trade’ nutrients with plants for energy e.g. by consuming energy-rich sugars and
other chemicals exuded by roots, or through more specialised structures such as rhizobia (that form
nitrogen fixing root nodules) and mycorrhizal associations (Stirling et al., 2016). Microbes also
compete with other soil organisms for resources (Dunn et al., 2006).
Substantial evidence exists that agricultural land use selects for different microbial
communities than those that develop in soils under native vegetation (Brackin et al., 2013; Jesus et
al., 2009; Nourbakhsh 2007). Microbe populations are reduced by 5070% in sugarcane soils
compared with adjacent forest soils (Brackin et al., 2014; Dominy et al., 2002; Holt and Mayer,
1998), resulting in sugarcane soils having lower substrate conversion (i.e. microbial enzyme)
activities and reduced capacity for litter decomposition (Brackin et al., 2013).
Reasons include:
(i) Plant litter inputs are reduced and less diverse in agricultural than natural systems;
(ii) Tillage negatively impacts on fungal hyphal networks and the larger soil fauna
(which may take a long time to re-establish);
(iii) Nutrients are supplied separately to carbon as mineral fertilisers rather than bound
together in organic materials as occurs in natural ecosystems; and
(iv) Many soil microbes are well adapted to decomposing organic materials; however,
their populations tend to decline with reduced substrate availability in agricultural
Instead, intensive monoculture systems tend to promote pathogenic soil microbes that specialise
in infecting a narrow range of host crops (Shipton 1977). As a result, pathogens are more competitive
and there are fewer organisms that control pathogen populations where a single crop is grown.
Brackin R et al. Proc Aust Soc Sugar Cane Technol Vol 39 2017
We define biologically healthy soils as those which support large and diverse microbial
communities, suppress pathogens, and support healthy crop development. Generally, the best
examples of these soils are those that are under (or have been recently cleared from) native
vegetation or pasture, experience low disturbance, and have high inputs of diverse organic
Table 1The role of soil organisms in ecosystem services (modified from Stirling 2014).
Decomposition of organic matter
Soil organisms macerate and decompose plant and animal residues. It is probably the
most important function of the soil biological community.
Soil formation, and stabilisation of aggregates
Soil microorganisms produce polysaccharide glues that shape soil structure and form
aggregates. Networks of fungal hyphae bind mineral and organic particles together
helping form macro-aggregates. The larger soil fauna act asengineers’, by moving or
ingesting soil, or creating mounds, casts and burrows.
Production, uptake and transfer of nutrients
Many soil organisms impact directly on plant nutrition. For example, many bacteria
are involved in nitrogen cycling; arbuscular mycorrhizal fungi promote the crops’
uptake of phosphorus and other nutrients; siderophore-producing bacteria chelate iron
and other bound nutrients to increase the availability for plants; and certain fungi and
bacteria solubilise phosphates, making them available to plants.
Storage and cycling of nutrients
When organic matter is decomposed, complex organic molecules are broken down
and eventually mineralised into smaller organic substances. During this process, some
nutrients are immobilised (i.e. incorporated into living cells). This process governs
the supply of nutrients to plants and nutrient equilibrium levels in soil are governed
by the soil biota.
Many soil organisms obtain sustenance from living roots. Most cause little damage to
crops, but some are important pests and pathogens.
Plant growth promotion and suppression of pests and pathogens
Rhizosphere inhabitants produce plant growth-promoting substances and endophytic
microorganisms induce resistance to pathogens.
Degradation of toxic compounds
Soil organisms produce enzymes that break down pesticides, pollutants and other
Biology of sugarcane soils
Biological components of soil quality decline were identified as early as 1930 in the
Australian Sugar Industry. Bell (1935) demonstrated in field and glasshouse experiments that virgin
land produced greater cane yields than long-term cane land. He found that long-term cane soil
responded strongly to fumigation (while forest soil did not), demonstrating a biological cause of
yield limitation.
This research was disrupted by WWII, and by the 1950s and 1960s, fertiliser application
rates were the primary avenue explored for improving soil fertility. Growers were encouraged to
increase fertiliser applications and avoid rotations (Yates 1963), and very low fertiliser prices
allowed growers to fertilise at high rates (Barrie 1963).
Brackin R et al. Proc Aust Soc Sugar Cane Technol Vol 39 2017
The increases in nutrient-input facilitated yield increases, but also masked the early signs of
the negative impacts of the intensification of the sugarcane monoculture (Garside et al., 2007;
Pankhurst et al., 2003).
A substantial effort into researching soil quality in the sugar industry took place in the late
1990s (the Yield Decline Joint Venture). This program found a broad range of soil constraints in
long-term sugarcane soils, falling into biological, chemical and physical categories. It was
confirmed that a lack of crop rotations from sugarcane monoculture results in changes to the soil
biological community composition that included a build-up of pathogens (Pankhurst et al., 2005;
Stirling, 2008), and decreased overall microbial populations (Holt and Mayer, 1998). Sugarcane
soils (and agricultural soils generally) have lower content of organic carbon compared with soils
under native vegetation or pasture (Dominy et al., 2002; Stirling et al., 2010). Because soil carbon
is the main energy source for soil microbes, loss of soil carbon and soil microbial populations are
strongly linked (Dominy et al., 2002).
Here we discuss some of the organisms that occur in soils under sugarcane production, the
key management options that influence their populations, the tools available for quantifying
changes in soil organism populations, and the need for a comprehensive approach to soil biology
research in sugarcane systems.
Key components of soil biology
Bacteria and Archaea (we use the collective term ‘bacteria’) constitute the greatest
component of soil microorganisms with population densities often several orders of magnitude
greater than fungi in number but not in biomass (Stirling et al., 2016). Bacteria have a large
metabolic diversity and fulfil a vast range of functions in soils, from decomposing organic matter
(making nutrients available to other soil organisms and roots), driving the soil nitrogen cycle,
synthesising plant growth promoting substances, being food sources for other organisms,
pathogens, or suppressing pests and diseases (Stirling et al., 2016).
There has been considerable interest in endophytic nitrogen-fixing bacteria for several
decades to supplement nitrogen supply in sugarcane. Brazilian studies suggest substantial
contributions can be made to the crop N budget (Boddey et al., 1995; Boddey et al., 1991).
However, these methodologies rely on numerous assumptions and are prone to error (Soper et al.,
2015). Australian research with Brazilian and Australian sugarcanes have failed to detect significant
nitrogen fixation (Walsh et al., 2006) or increases in the abundance or activity of N-fixing bacteria
in soils receiving low N fertiliser rates (Yeoh et al., 2015).
A number of plant growth promoting rhizobacteria (PGPR) have been isolated from
sugarcane roots and can promote vigour in controlled conditions in laboratory or glasshouse, either
through nitrogen fixation, hormone production or both (Mehnaz, 2011; Paungfoo-Lonhienne et al.,
2014). While there is good evidence that PGPR can substantially stimulate yield increases in
laboratory or glasshouse (Siddiqui, 2005), few PGPR have been trialled successfully in commercial
sugarcane crops. Across numerous crops, variable results occur and reasons include that
competitive interactions from other microorganisms can prevent benefits from PGPR (Saharan and
Nehra, 2011).
In Brazil, bacterial inocula of five or more PGPR including putative N-fixing
Gluconacetobacter, Azospirillum, Herbaspirillum and Bulkholderia species have undergone many
years of scientific evaluation. These commercial inocula are now used routinely but require several
inoculation steps in each crop cycle that span from soaking setts in the inoculum to injection of soil,
and their formulation accommodates particular sugarcane varieties and soil types to ensure efficacy
(Schultz et al., 2014).
Globally, R&D into PGPR is expanding, and substantial progress is foreseeable. Scientific
investigations are enabling the manufacture of inocula that are effective for specific crop varieties,
soils and climates as formulation, storage and application techniques are being optimised.
Brackin R et al. Proc Aust Soc Sugar Cane Technol Vol 39 2017
In markets such as Europe, where companies selling microbial inoculum are required to
prove efficacy to government regulators, robust science is underway and PGPR are increasingly
part of horticultural and broad acre crop production.
Bacteria may also act as biological control agents. For example, the bacterium Pasteuria
penetrans parasitises nematodes and reduces the ability of crop-damaging nematodes to reproduce
(Stirling, 2014). While Pasteuria penetrans is relatively common in cane soils in Australia, it rarely
occurs at high population densities, presumably because tillage disrupts the intimate relationship
between the parasite and its nematode host (Stirling et al., 2016). It would be highly desirable for
the industry if populations of Pasteuria penetrans can be increased to provide effective biological
control of parasitic nematodes, and research is ongoing (Anderson et al., unpublished results).
Bacteria may be pathogens where there is a specific host pathogen relationship (Agrios,
2005) in addition to deleterious rhizosphere bacteria, which negatively affect plant growth and
vigour through the production of toxins and hormones, competition for nutrients and inhibiting
beneficial mycorrhizal fungi (Lehman et al., 2015). How much there is yet to learn about soil
bacteria (and their prokaryotic counterparts Archaea) is highlighted in the recent Biomes of
Australian Soil Environments (BASE) project (Bissett et al., 2011). While similar higher-order
bacterial and Archaea groupings occur across land uses, including sugarcane soil, bacterial
communities have yet to be characterised in depth. The BASE project provides genetic sequences,
contextual data as well as search tools that allow researchers to interrogate Australia’s first soil
microbial diversity database for numerous applications.
Fungi are recognised key players in soil function, as their hyphae structures span large
distances in soil, decompose recalcitrant substrates and contribute to soil carbon sequestration
(Fontaine et al., 2011; Frey et al., 2003). Fungi are particularly sensitive to disturbance such as
tillage, as they tend to be comparatively slow growing with mycelial networks regenerating slowly
after disturbance (Beare et al., 1997). Agronomic practices such as nitrogen fertiliser rate can affect
fungal community composition in sugarcane fields, with higher N rates resulting in a decreased
proportion of Basidiomycota (filamentous hyphae-based fungi, which include lignin decomposers)
and increases in Ascomycota and putative crop pathogenic fungi (Paungfoo-Lonhienne et al.,
A range of fungal organisms are associated with sugarcane roots some are pathogenic but
the majority are beneficial (Rutherford et al., 2002). Beneficial fungi such as Trichoderma species
are common rhizosphere inhabitants. Trichoderma species have been widely studied for their
capacity to produce antibiotics, parasitise other fungi and compete with deleterious plant
microorganisms such as Rhizoctonia and Fusarium (Contreras-Cornejo et al., 2016).
In sugarcane fields treated with filter cake (mill-mud), Trichoderma species are among the
first fungal colonisers of mill-mud and are suppressive to Pythium and nematodes (Roth, 1971;
Sharon et al., 2001). Other potentially beneficial fungi that are abundant in sugarcane soil include
non-pathogenic Fusarium, nematode trapping fungi (Arthrobotrys species, Dectylella spp,
Beauveria spp, and Metarhizium (Rutherford et al., 2002; Stirling, 2014).
Fungal organisms that form association with plants, and that live entirely or for part of their
life cycle in plants, but cause no apparent harm, are known as endophytes. These endophytic fungi
form symbiotic relationships with the host plant, provide a range of beneficial services such as
enhanced nutrient uptake, drought tolerance and disease resistance (Stirling, 2014).
Fusarium sacchari and Epicoccum nigrum are effective in controlling several fungal
pathogens and insect pest African sugarcane borer, Eldana saccharina (de Lima Favaro et al. 2012;
Mahlanza et al., 2015). Mycorrhizal fungi are a particular example of endophytes and benefits in
assisting in phosphorus uptake, stress tolerance and nematode suppression have been documented in
sugarcane, including in Australia (Kelly et al., 1997; Sankaranarayanan and Hari, 2016). Overall,
there is surprisingly little known about the presence and effects of mycorrhizal endophytes in
Brackin R et al. Proc Aust Soc Sugar Cane Technol Vol 39 2017
Australian sugarcane crops, and a recent study found that endomycorrhizal fungi (Glomeromycota)
were absent from soil and roots of two commercial sugarcane fields (Paungfoo-Lonhienne et al.,
2015). Whether this observation reflects the situation in the industry as a whole is unknown. It also
remains to be investigated whether commercial mycorrhizal inoculum can successfully re-introduce
endomycorrhizal species if these are indeed scarce or missing from Australian sugarcane soils.
A small number of pathogenic soil fungi can impact substantially on sugarcane yield.
Pachymetra root rot (Pachymetra chounorhiza) is widely spread across Australian sugarcane
growing regions and can cause significant yield loss if susceptible sugarcane varieties are planted,
and no other known control measures are effective against this pathogen (Croft and Magarey,
2000). Pineapple sett rot (Ceratocystis paradoxa) can cause considerable damage at emergence of
sugarcane in favourable conditions (Girard and Rott, 2000).
Various species of Trichoderma and Gliocladium fungi were found to be effective in
controlling pineapple sett rots under controlled growth conditions, but their effectiveness under
field conditions has yet to be proven (Girard and Rott, 2000). Pythium root rot (Pythium spp.) is
only a problem in wet temperate climates and the severity of Pythium root rot is controlled by
interaction with soil organisms and organic matter (Hoy, 2000).
Magarey (1996) identified a range of pathogens (sub-clinical pathogens) which were
affecting root surfaces and leading to poor root growth and yield decline of sugarcane. It is likely
that conventional farming systems provide conditions favouring sub-clinical pathogens with soil
compaction, lack of organic matter, anoxia and crop monoculture as potential contributing factors.
Magarey (1996) recommended research on further identification of these sub-clinical
pathogens and on the management practices that influence this group of pathogens; however this
has not yet occurred.
Sugarcane is largely grown as a constant monoculture with only a few months of break
every three to 10 years, resulting in favourable conditions for the development of large nematode
communities. More than 310 species of 48 genera of endo- and ectoparasitic nematodes have been
recorded from sugarcane roots and/or rhizosphere (Cadet and Spaull, 2005).
The most common plant parasitic nematodes that are widespread in sugarcane fields are
Pratylenchus and Meloidogyne species (Stirling and Blair 2000).
Other genera that are particularly widespread in sugarcane fields include, Helicotylenchus
(35 species), Tylenchorhynchus (36 spp.), Xiphinema (52 spp.), Hoplolaimus (11 spp.),
Paratrichodorus and Trichodorus (nine spp.) (Cadet and Spaull, 2005).
Nematodes associated with sugarcane do not occur alone in the soil but are present in
communities comprising a number of species. Surveys from various parts of the world show that
the number of nematode genera present in a single soil sample ranges from one to 12 with an
average of between 3.2 and 7.9 (Cadet and Spaull, 2005). These show the wide diversity and
complexity of plant parasitic nematodes associated with sugarcane roots and rhizosphere.
Free-living nematodes that are often regarded as beneficial form part of the sugarcane
rhizosphere community. In most sugarcane soils free-living nematodes are present in lower
numbers compared with plant parasitic nematodes, representing 30–70% of total nematode
population (Cadet and Spaull, 2005; Stirling et al., 2001; Stirling et al., 2002).
Some free-living nematodes are predacious and others are a food source for fungal predators
of nematodes, and this may have been one of the reasons why populations of plant parasitic
nematodes were suppressed when numbers of free-living nematodes were increased by adding
organic matter to soil (Stirling and Eden, 2008).
An inverse relationship between nitrogen fertiliser and beneficial nematodes was observed
with a lower presence of beneficial nematodes in soil receiving 160 kg N per hectare than soil
fertilised with only 40 kg N/ha (Stirling et al., 2015).
Brackin R et al. Proc Aust Soc Sugar Cane Technol Vol 39 2017
Microarthropods, a size-based class variously defined but generally recognised as being
composed of mites, springtails, and very small insects, arachnids and myriapods, are considered
significant indicators of soil health because of their abundance (typically hundreds of thousands in
the upper 10 cm of a square metre of healthy soil), diversity (typically hundreds of species), and
diversity of function. Perhaps their most important function is maintaining and stoking the
microbial decomposer engine by penetration and comminution of litter, stimulatory grazing of
microbes, and dispersal of microbial propagules.
Another important function is the regulation of grazer populations by predators and, of
special interest to agricultural systems, the suppression of root pathogens including nematodes
(Stirling et al. 2016). In sugarcane soils, microarthropods have barely been studied, but see Stirling
et al. (2016) and Walter and Proctor (2013) for recent overviews of their function and importance in
other systems. Manwaring et al. (2015) show preliminary results from Australian sugarcane fields
and conclude that sugarcane soils contain a microarthropod community with potential to contribute
to the suppression of nematode pests.
Earthworms are often considered indicators of soil health, and are regarded as ‘ecosystem
engineers’ due to their ability to maintain soil structure and improve aeration and water infiltration
(Kibblewhite et al., 2008; Stork and Eggleton, 1992). Earthworm numbers are increased in
abandoned or reforested sugarcane fields compared with managed fields (Zou and Bashkin, 1998),
and numbers tend to decrease in fields after tilling due to soil disruption and drying (Kibblewhite et
al., 2008; Stork and Eggleton, 1992).
Conversely, there are indications that earthworm numbers are correlated at least as strongly
with soil moisture than with land management (Carnovale et al., 2015), and thus may not always be
reliable indicators. In Indonesian sugarcane fields receiving different qualities and quantities of
organic matter, earthworm numbers varied in response to inputs, with higher numbers of
earthworms observed with larger amounts and lower quality litter (Nurhidayati et al., 2012). The
importance of earthworms as soil engineers is not reflected by current research efforts in Australia
and there is much scope to expand knowledge with targeted comparisons across soil types and
agronomies and in context with other soil biology indicators.
Improving soil biology
All of the organisms described above and others (e.g. beetles, protozoa) that have not been
outlined here, interact to form a soil food web (Figure 2). While soil structure, soil water content,
pH and soil temperature play roles in the structure of the food web, the primary driver of activity
within the soil food web is organic matter, in which carbon is an energy source for the remainder of
the food web (Stirling, 2014).
While crop residues (especially sugarcane trash) are the major contributor to organic matter
input, living plants continuously contribute a substantial amount of labile organic matter through
root exudates and root turnover; around 11% of the net fixed carbon produced by plants is on
average deposited by roots into the soil (Jones et al., 2009). This is why it is important to not only
return crop residues to the soil, but also to maintain both crop and rotation species cover to maintain
organic matter inputs to soil and improve soil biology.
The Yield Decline Joint Venture recommended that growers adopt green cane trash
blanketing and legume rotations, minimum tillage, wider (1.8 m) row spacing and GPS guidance to
restrict the area subject to soil compaction. While green cane trash blanketing is now widely
adopted (except in the Burdekin growing region) (Pankhurst et al., 2003; Salter et al., 2010;
Schroeder et al., 2009), the proportion of growers using rotations to other crops remains a minority
(Bell et al., 2007). While trash blanketing is considered to positively affect soil health, field studies
(Robertson and Thorburn, 2007; Salter et al., 2010) have shown no changes in soil carbon levels
over an 18 year period of trash blanketing (Page et al., 2013), and the fate of trash blanket derived C
Brackin R et al. Proc Aust Soc Sugar Cane Technol Vol 39 2017
and N remain a matter of debate. Very few sugarcane growers have adopted the recommendations
of the Yield Decline Joint Venture in their totality, and, in many cases, a partial adoption may have
little effect (i.e. if trash blanketing is adopted, conventional tillage may still be used). Increasing soil
carbon remains a challenge in most systems worldwide and the drivers of soil carbon sequestration
are not yet fully understood. However, it is becoming increasingly apparent that the soil microbial
community – and particularly fungi has a major influence on the ultimate fate of carbon entering
the soil (Cotrufo et al., 2013; Fontaine et al., 2011; Stockmann et al., 2013).
A large number of tests for biological activity in soil and biodiversity have been developed,
including microbial biomass, fungal biomass, fungal-bacterial ratios, microbial and fungal diversity,
number and diversity of earthworms, free-living nematode counts, CO2 respiration, total organic
carbon, labile carbon, biochemical tests of microbial activity, the ratio of bacterial feeding
nematodes to fungal feeding nematodes, and tests for mycorrhizal fungi (Obriot et al., 2016; Ritz et
al., 2009).
For non-experts, the nuances of these assays are often lost and they are often
interchangeably considered as measures of ‘biology’. However, if the tests are grouped and overlaid
on the soil food web (Figure 2) then the relevance of the various tests becomes clearer. For
example, a nematode community analysis, where omnivorous and predatory nematodes are
dominant to plant parasitic nematodes, indicates a healthy soil food web. A nematode community
analysis that has a dominance of certain groups of bacterial-feeding nematodes is evidence of a soil
that has been recently disturbed or where there have been recent large inputs of organic matter
(Stirling, 2014). Similarly, ratios of fungal:bacterial biomass are more strongly skewed towards
bacteria in disturbed systems, as fungi are more strongly impacted (Bardgett and McAlister, 1999).
Microbes produce enzymes to decompose organic substrates, and the range of enzyme
activities of fungi and bacteria present can be informative about both the current factors limiting
microbial growth, and the availabilities of various chemicals in soils (Brackin et al., 2013). For
example, if many microbes are present that degrade plant cell walls, then then an assay for the
enzyme cellulase will return high values. Other assays (such as fluorescein diacetate hydrolysis)
measure the sum activity of a broad range of enzymes and can be useful general indicators of
microbial activity.
Healthy soils in general have larger microbial populations, higher fungal:bacterial ratios and
higher levels of production of a range of enzymes. CO2 production is frequently used as a measure
of soil microbial activity and of other processes, such as decomposition, mineralisation, and even as
a microbial biomass estimate. In reality, CO2 production is the integrated end result of almost all
soil activity by the entirety of living organisms in soil, including respiration from plant roots. It can
be a useful general indicator of overall soil activity, as it is relatively easy to measure, but, like all
soil biological measurements, is highly dependent on soil moisture. Connecting the various
measures of soil biological composition and function requires greater data integration and
Future vision and recommendations
While overall soil biological populations decline quickly and community structure changes
rapidly under intensive agricultural land use (Dominy et al., 2002; Holt and Mayer, 1998), re-
establishing a healthy soil biological community in degraded soils can be an extremely slow process
(Fichtner et al., 2014).
Many growers understandably look towards ‘quick fix’ commercial products; however these
are largely unproven and are unlikely to produce positive results, particularly if introduced into an
adverse soil environment that challenges the crop with physical and chemical constraints. There is
also currently not a one-stop-shop for sugarcane growers to measure indicators of soil biology and a
lack of cane-specific recommendations for growers to be able to benchmark their progress. The
grain industry’s Soil Quality project offered tests for total organic carbon, labile carbon, microbial
biomass carbon, soil nitrogen supply, and specific tests for take-all and rhizoctonia diseases, as
Brackin R et al. Proc Aust Soc Sugar Cane Technol Vol 39 2017
well as tests for cereal cyst and root lesion nematodes. A traffic light system was developed to help
growers identify what they should address in the first instance (Murphy, 2012). To advance the
understanding of soil biology in sugarcane, assessment is required of various agronomic measures
together with considerable numbers of soil samples from different regions and soil types. Sampling
and benchmarking also has to reflect the transition from traditional to modern farming systems in
context of yield and agronomies to be of use for growers.
Fig. 2—The soil food web with various indicators of soil health overlaid (black boxes).
Recommendations include:
1. Collect and assess a range of soils and set benchmarks – ideally, a large collection of
samples of different soil types from different production regions from traditional and
new farming systems assessed collectively with a large range of physical, chemical
and biological indicator tests. These data allow us to identify which measures are the
most suited to sugarcane systems (easy to use and interpret, economical). They will
also provide benchmarks for the various soil types and districts. Such a
comprehensive data set would be combined with yield data and provide information
on the best practices for growers to implement to improve soil biology.
2. Expand research on cover crops research on cover crops should be expanded to
understand the role that legume break crops have in providing nitrogen to subsequent
cane crops, determine suitable cover crops to break pest and disease cycles and
examine the impact of cover crops on increasing soil biological diversity.
Brackin R et al. Proc Aust Soc Sugar Cane Technol Vol 39 2017
3. Expand research on interactions within the soil food web there is need to better
understand how components of the soil food web interact, for example, there is some
evidence that plant parasitic nematodes increase the susceptibility of sugarcane roots
to sub-clinical pathogens (Stirling, 2008).
In summary, sugarcane soils have diverse communities that contribute to the overall health
of the soil through functions such as nutrient cycling, and pest and disease suppression. Growers
can undertake practices to improve their soils’ biology, but they need the tools to effectively direct
changes and identify which practices will have the biggest benefit.
The quest for not only improving resource use in cropping for farm economic and
environmental benefits, but also consider ecosystem services as a whole (i.e. carbon sequestration
into soils, greenhouse gas fluxes, water infiltrations, nutrient cycling) is increasingly providing a
new framework, where growers are connected to the global community including earth system
With problems identified and articulated, next steps can now capitalise on powerful
molecular and data analysis tools to characterise soil biological communities to advance the tool kit
for growers.
Dr Graham Stirling is thanked for his very helpful comments on drafts of this paper. Sugar
Research Australia is acknowledged for funding project 2014/004, on which David Walter, Shamsul
Bhuiyan and Jay Anderson collaborated with Graham Stirling. Scott Buckley is funded by SRA
project 2014/108.
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... Brackin et al. (2017). Soil biological health-what is it and how can we improve it? ...
... The soil food web with various indicators of soil health overlaid (black boxes). Source:Brackin et al. (2017). Soil biological health-what is it and how can we improve it? ...
... The soil with the ability to meet plant and ecosystem requirements for water, aeration, and strength over time, and to resist and recover from processes that might diminish this ability is considered as physically healthy (McKenzie et al., 2011;. Soil biological health is the ability of soil to support large and diverse microbial communities, suppress pathogens, and support healthy crop development (Brackin et al., 2017); while chemically healthy soil has plant nutrients in optimum quantity, available form, and balanced proportions, and which are available to plants without the hindrance of other chemical compound and properties. Soil chemical health also considers the presence or absence of harmful soil agrochemicals and pollutants. ...
... The major difficulties in determining soil biological health and evaluating the indicators of soil biological health mentioned by Brackin et al. (2017) are as follows: ...
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Soil is an important natural resource providing water, nutrient, and mechanical support for plant growth. In agroecosystem, continuous manipulation of soil is going on due to addition of input, removal of nutrients, changing water balance, and microbial life. These processes affect soil properties (physical, chemical, and biological), and the deviation of these properties from the normal status is controlled by soil buffering capacity and soil resilience. If these changes are beyond the reach of soil resilience, then soil loses its original state, leading to soil degradation. At present, the extent of the degraded area in the world is 1,036 to 1,470 million ha. This urges the need for maintaining soil health rather than the mere addition of input for crop production. Soil health is an integrative property that reflects the capacity of soil to respond to agricultural intervention, so that it continues to support both agricultural production and the provision of other ecosystem services. Maintaining the physical, chemical, and biological properties of soil is needed to keep it healthy, and this is possible through the adoption of different agronomic approaches. The diversification of nutrient sources with emphasis on organic sources, adoption of principles of conservation agriculture, enhancement of soil microbial diversity, efficient resource recycling through the integrated farming system, and amendment addition for correcting soil reactions are potential options for improving soil health, and are discussed in this review. This article reviewed the concept of soil health and its development, issues related to soil health, and indicators of healthy soil. At the same time, the impact of the ill health of the soil on crop productivity and resource use efficiency reported in different parts of the world in recent years are also reviewed. The agro-techniques such as green and brown manuring in arable land and agroforestry on degraded and marginal land were followed on piece meal basis and for economic gain. The potential of these and several other options for maintaining soil need to be recognized, evaluated, and quantified for their wider application on the front of soil health management avenues. The use of crop residue, agro-industrial waste, and untreated mineral or industrial waste (basic slag, phosphogypsum, etc.) as soil amendments has a huge potential in maintaining healthy soil along with serving as sources of crop nutrition. The review emphasizes the evaluation and quantification of present-day followed agro-techniques for their contribution to soil health improvement across agro-climatic regions and for wider implications. Furthermore, emphasis is given to innovative approaches for soil health management rather than mere application of manures and fertilizers for crop nutrition.
... Keech et al. (2005) showed a high proportion of micropores of <50 μm in biochar produced at 450°C from common boreal tree species. Soil organisms, on the other hand, range in size from bacteria that are less than 2 μm, to grazers of microbes such as protozoa and nematodes that can be over 100 μm in diameter, as well as larger arthropods (Brackin et al., 2017;Paul, 2007). It has been proposed that biochar microporosity may act as a natural refuge for microorganisms from predation from grazers in cases where pore sizes limit the access to larger soil animals that would otherwise exert top-down control (i.e., the "microbial refugia hypothesis", Hockaday et al., 2007;Warnock et al., 2007;Zackrisson et al., 1996). ...
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It is well established that application of biochar to soils can promote soil fertility, which ultimately may enhance plant growth. While many mechanisms have been proposed to explain this, one specific mechanism, the “microbial refugia hypothesis” suggests that biochar may provide physical protection for soil microbe from soil micro‐fauna that otherwise exert top‐down control on microbial biomass and activity. We tested the microbial refugia hypothesis by incubating two boreal soils with and without biochar derived from a wood mixture of boreal tree species (Picea abies and Pinus sylvestris), and with and without soil nematodes. We measured phospholipid fatty acids (PLFA) as a relative measure of microbial biomass, and several variables indicative of microbial activity, including extractable nutrient concentrations (NH4+, NO3‐, and PO4‐), heterotrophic N2‐fixation, and soil respiration. Contrary to our expectations, we found that biochar by itself did not stimulate microbial biomass or activity. Further, we found that nematode addition to soil stimulated rather than depressed the biomass of several bacterial PLFA groups. Finally, interactive effects between the nematode treatment and biochar never worked in a way that supported the microbial refugia hypothesis. Our findings suggests that a typical boreal biochar applied to boreal soils may not have the same stimulatory effect on microbial biomass and activity that has been shown in some other ecosystems, and that enhanced plant growth in response to biochar addition sometimes observed in boreal environments is likely due to other mechanisms, such as direct nutrient supply from biochar, or amelioration of soil pH.
... Living soil carbon (C) pool, width chart. (Modifed fromBrackin et al. 2017.) The root tip rhizosphere, a hotspot of root exudate release and exudate turn over by endocellular enzymatic (ENCenz) and exocellular enzymatic (EXCenz) activities. ...
... Though soil biology has been an important component in the soil health discussion, it is only in the last few decades with an enhanced focus on soil health and advancements in soil microbiological techniques that biological indicators are now front-runners in deciphering the health of soils. Many biological processes are responsible for important soil functions, such as decomposition of organic matter, mineralization of and recycling of nutrients, nitrogen fixation, detoxification of pollutants, maintenance of soil structure, and biological suppression of plant pests and parasites (Brackinic et al., 2017). These processes are also closely linked to both the chemical and physical properties of soils. ...
Humanity thrives when soils are healthy as soils provide food, fiber, shelter, and a life-sustaining climate. Awareness of the need to optimize soil functions to grow food for an expanding human population and a desire to sustain environmental quality has led to an intense interest among stakeholders and practitioners in enhancing soil health. The public has become aware of soil health only in the last few years; however, for the seasoned soil scientists and agronomists, the journey to improve soil health began a long time ago, starting with the Dust Bowl Era and later to what was called soil quality movement. This article aims to review our current understanding of soil health by examining the history and evolving definition of soil health and then exploring the best soil health indicators from the physical, chemical, and biological domains that could be used to support practices for enhancing soil functions. Improving soil health will enhance soil functions, and so the conclusion that improving soil health involves enhancing soil organic carbon is justified. We briefly review the various soil health indicators and management options for enhancing soil health and explore. the social and economic perspectives of the call for farmers to use soil health practices. We conclude the review by examining the current knowledge gaps and suggesting ways to advance soil health understanding and conversation. For the agricultural community, we present a new definition of soil health as the capacity of soils to provide a sink for carbon to mitigate climate change and a reservoir for storing essential nutrients for sustained ecosystem productivity.
... Mineralisation of N can vary from season to season within a site (Allen et al. 2005), and rates are influenced by environmental factors such as soil moisture and temperature. It can be affected by agricultural management such as tillage, organic matter additions and fertiliser application (Silgram and Shepherd 1999), although no differences in mineralisation rate were found between fertilised and unfertilised fields in this study, potentially because N mineralisation is primarily driven by soil microbial C demand rather than N limitation (Schimel and Weintraub 2003;Brackin et al. 2017b). ...
Cotton cropping systems in Australia have poor nitrogen (N) use efficiency, largely due to over-application of N fertiliser. The N mineralisation from soil organic N reserves is often overlooked, or underestimated despite recent studies indicating that it may contribute the majority of N exported with the crop. Predicting N mineralisation is a major challenge for agricultural industries worldwide, as direct measurements are time-consuming and expensive, but there is considerable debate as to the most reliable methods for indirect estimation. Additionally, laboratory incubations assess potential (rather than actual) mineralisation, and may not be representative of N cycling rates in the field. We collected 177 samples from most major Australian cotton growing regions, and assessed their mineralisation potential using ex situ laboratory incubations, along with an assessment of potential indicators routinely measured in soil nutrient tests. Additionally, at three unfertilised sites we conducted in situ assessment of mineralisation by quantifying soil N at the beginning of the growing season, and soil and crop N at the end of the season. We found that Australian cotton cropping soils had substantial mineralisation potential, and that soil total N and total carbon were correlated with mineralisation, and have potential to be used for prediction. Other potential indicators such as carbon dioxide production and ammonium and nitrate concentrations were not correlated with mineralisation. In parallel studies of ex situ and in situ mineralisation, we found ex situ laboratory incubations overestimated mineralisation by 1.7 times on average. We discuss findings in terms of management implications for Australian cotton farming systems.
... Despite this challenge, biological associations continually demonstrate many important soil functions. Six key roles of soil microbes are: decomposition of organic matter (crop residue), mineralization of and recycling of nutrients, fixation of nitrogen, detoxification of pollutants, maintenance of soil structure, biological suppression of plant pests, and reducing parasitism and damage to plants (Stirling, 2014;Brackin et al., 2017). These functions are also very closely linked with both the chemical and physical properties of soil as they are dependent upon and contribute to the fluxes and flows of indicators such as pH, nutrients, soil structure, and aggregate stability, to name a few. ...
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Hundreds of thousands of little creatures live in soils. Some eat live plants, live animals, or both. Others, called decomposers, consume dead plants, and the waste of other living beings (their feces and their dead bodies), and transform them into food for plants. The health of soils depends largely on the presence of decomposers, and thus it is necessary to study how these creatures may be affected by climate change. To this end, we built a new type of traps to catch live soil animals, which we called cul-de-sac and basket traps. Here, we show how these traps are better for studying animal activity (how much they move in the soil) compared to the most used devices to date, pitfall traps. Comparatively, our traps capture more active animals and prevent predators from killing prey inside, which will improve the accuracy of future studies all over the world.
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Trophic interactions are crucial for carbon cycling in food webs. Traditionally, eukaryotic micropredators are considered the major micropredators of bacteria in soils, although bacteria like myxobacteria and Bdellovibrio are also known bacterivores. Until recently, it was impossible to assess the abundance of prokaryotes and eukaryotes in soil food webs simultaneously. Using metatranscriptomic three-domain community profiling we identified pro- and eukaryotic micropredators in 11 European mineral and organic soils from different climes. Myxobacteria comprised 1.5–9.7% of all obtained SSU rRNA transcripts and more than 60% of all identified potential bacterivores in most soils. The name-giving and well-characterized predatory bacteria affiliated with the Myxococcaceae were barely present, while Haliangiaceae and Polyangiaceae dominated. In predation assays, representatives of the latter showed prey spectra as broad as the Myxococcaceae . 18S rRNA transcripts from eukaryotic micropredators, like amoeba and nematodes, were generally less abundant than myxobacterial 16S rRNA transcripts, especially in mineral soils. Although SSU rRNA does not directly reflect organismic abundance, our findings indicate that myxobacteria could be keystone taxa in the soil microbial food web, with potential impact on prokaryotic community composition. Further, they suggest an overlooked, yet ecologically relevant food web module, independent of eukaryotic micropredators and subject to separate environmental and evolutionary pressures.
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Ameliorating biological attributes of agricultural soils is desirable, and one avenue is introducing beneficial microbes via commercial biostimulant products. Although gaining popularity with farmers, scientific evaluation of such products in field-grown crops is often lacking. We tested two microbial products, Soil-Life™ and Nutri-Life Platform®, in a commercial sugarcane crop by profiling bacterial and fungal communities in soil and roots using high throughput phylogenetic marker gene sequencing. The products, one predominantly consisting of Lactobacillus and the other of Trichoderma, were applied as a mixture as per manufacturers’ instructions. Additives included in the formulations were not listed, and plots that did not receive the product mixture were the controls. The compositions of bacterial communities of soil and sugarcane roots, sampled 2, 5 and 25 weeks after application, were unaffected by the products. Soil fungal communities were also unaffected, but sugarcane roots had a greater relative abundance of three unidentified taxa in genera Marasmius, Fusarium and Talaromyces in the treated plots. Sugarcane yield was similar across all treatments that included a 25% lower nitrogen fertiliser rate. Further research must examine if the altered root fungal community is a consistent feature of the tested products, and if it conveys benefits. We conclude that putative biostimulants can be evaluated by analysing the composition of microbial communities. DNA profiling should be complemented by cost-benefit analysis to build a public information base documenting the effects of microbial biostimulants. Such knowledge will assist manufacturers in product development and farmers in making judicious decisions on product selection, to ensure that the anticipated benefits of microbial biostimulants are realised for broad acre cropping.
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The sugarcane industry, a strategic crop in Brazil, requires technological improvements in production efficiency to increase the crop energy balance. Among the various currently studied alternatives, inoculation with diazotrophic bacteria proved to be a technology with great potential. In this context, the efficiency of a mixture of bacterial inoculant was evaluated with regard to the agronomic performance and N nutrition of sugarcane. The experiment was carried out on an experimental field of Embrapa Agrobiologia, in Seropedica, Rio de Janeiro, using a randomized block, 2 x 3 factorial design (two varieties and three treatments) with four replications, totaling 24 plots. The varieties RB867515 and RB72454 were tested in treatments consisting of: inoculation with diazotrophic bacteria, N-fertilized control with 120 kg ha(-1) N and absolute control (no inoculation and no N fertilizer). The inoculum was composed of five strains of five diazotrophic species. The yield, dry matter accumulation, total N in the shoot dry matter and the contribution of N by biological fixation were evaluated, using the natural N-15 abundance in non-inoculated sugarcane as reference. The bacterial inoculant increased the stalk yield of variety RB72454 similarly to fertilization with 120 kg ha(-1) N in the harvests of plant-cane and first ratoon crops, however the contribution of biological N fixation was unchanged by inoculation, indicating that the benefits of the inoculant in sugarcane may have resulted from plant growth promotion.
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The study describes the primary assembly of arbuscular mycorrhizal communities on a newly constructed island Peberholm between Denmark and Sweden. The AM fungal community on Peberholm was compared with the neighboring natural island Saltholm. The structure of arbuscular mycorrhizal communities was assessed through 454 pyrosequencing. Internal community structure was investigated through fitting the rank-abundance of Operational Taxonomic Units to different models. Heterogeneity of communities within islands was assessed by analysis of group dispersion. The mean OTU richness per sample was significantly lower on the artificial island than on the neighboring natural island, indicating that richness of the colonizing AM fungal community is restricted by limited dispersal. The AM fungal communities colonizing the new island appeared to be a non-random subset of communities on the natural and much older neighboring island, which points to high colonization potential of certain – probably early successional – mycorrhizal fungi, likely assisted by migratory birds.
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Plant growth-promoting rhizobacteria (PGPR) are naturally occurring soil bacteria that aggressively colonize plant roots and benefit plants by providing growth promotion. Inoculation of crop plants with certain strains of PGPR at an early stage of development improves biomass production through direct effects on root and shoots’ growth. Inoculation of ornamentals, forest trees, vegetables, and agricultural crops with PGPR may result in multiple effects on early-season plant growth, as seen in the enhancement of seedling germination, stand health, plant vigor, plant height, shoot weight, nutrient content of shoot tissues, early bloom, chlorophyll content, and increased nodulation in legumes. PGPR are reported to influence the growth, yield, and nutrient uptake by an array of mechanisms. They help in increasing nitrogen fixation in legumes, help in promoting free-living nitrogen-fixing bacteria, increase supply of other nutrients, such as phosphorus, sulphur, iron and copper, produce plant hormones, enhance other beneficial bacteria or fungi, control fungal and bacterial diseases and help in controlling insect pests. There has been much research interest in PGPR and there is now an increasing number of PGPR being commercialized for various crops. Several reviews have discussed specific aspects of growth promotion by PGPR. In this review, we have discussed various bacteria which act as PGPR, mechanisms and the desirable properties exhibited by them.
The objective was to develop a multi-criteria tool to compare fertilizing practices either based on mineral fertilizer (CONT + N) or repeated applications of exogenous organic matter (EOM) and considering the positive but also the negative impacts of these practices. Three urban composts (a municipal solid waste or MSW, a co-compost of sewage sludge and green waste (GWS), and biowaste (BIO)) and a farmyard manure (FYM) have been applied biennially over 14 years. Soils and crops were sampled repeatedly and >100 parameters measured. The development of different quality indices (QI) was used to provide a quantitative tool for assessing the overall effects of recycling different types of EOM. A minimum data set was determined and 7 indices of soil and crop quality were calculated using linear scoring functions: soil fertility, soil biodiversity, soil biological activities, soil physical properties, soil contamination (“available” and “total”) and crop productivity. All QI varied between 0 and 1, 1 being the best score. EOM amendments significantly increased soil biodiversity, biological activities and physical properties with intensity generally depending on their characteristics. FYM was the most efficient EOM to improve soil biological properties. EOM application lead to similar yields as mineral fertilizers but grain quality was slightly decreased. Thus, mineral fertilizers remained more efficient at improving crop productivity index (QI = 0.88) than EOM although BIO was not significantly different than CONT + N. All EOM improved soil fertility but only BIO was significantly higher (QI = 0.86). EOM added a range of nutrients but an excess of P (e.g. GWS) can negatively impact the soil fertility index. EOM negatively affected the soil contamination index when considering total concentrations but decreased available fractions and consequently the risks of transfer. BIO was the most efficient EOM for most indices including improving the index of “available” soil contamination. This study demonstrated the positive impact of repeated EOM applications on soil and crop quality in a loamy soil.
Trichoderma spp. are common soil and root inhabitants, which have been widely studied due to their capacity to produce antibiotics, parasitize other fungi, and compete with deleterious plant microorganisms. These fungi produce a number of secondary metabolites such as non-ribosomal peptides, terpenoids, pyrones and indolic-derived compounds. In the rhizosphere, the exchange and recognition of signaling molecules by Trichoderma and plants may alter physiological and biochemical aspects in both. For example, several Trichoderma strains induce root branching and increase shoot biomass as a consequence of cell division, expansion and differentiation by the presence of fungal auxin-like compounds. Furthermore, Trichoderma, in association with plant roots, can trigger systemic resistance and improve plant nutrient uptake. The present review describes the most recent advances in understanding the ecological functions of Trichoderma spp. in the rhizosphere at biochemical and molecular levels with special emphasis in their associations with plants. Finally, through a synthesis of the current body of work, we present potential future research directions on studies related to Trichoderma spp. and their secondary metabolites in agroecosystems.
This fifth edition of the classic textbook in plant pathology outlines how to recognize, treat, and prevent plant diseases. It provides extensice coverage of abiotic, fungal, viral, bacterial,nematode and other plant diseases and their associated epidemiology. It also covers the genetics of resistance and modern management on plant disease.Plant Pathology, 5th Edition, is the most comprehensive resource and textbook that professionals, faculty and students can consult for well-organized, essential information. This thoroughly revised edition is 45% larger, covering new discoveries and developments in plant pathology and enhanced by hundreds of new color photographs and illustrations.
More than 40,000 species of mites have been described, and up to 1 million may exist on earth. These tiny arachnids play many ecological roles including acting as vectors of disease, vital players in soil formation, and important agents of biological control. But despite the grand diversity of mites, even trained biologists are often unaware of their significance. Mites: Ecology, Evolution and Behaviour (2nd edition) aims to fill the gaps in our understanding of these intriguing creatures. It surveys life cycles, feeding behaviour, reproductive biology and host-associations of mites without requiring prior knowledge of their morphology or taxonomy. Topics covered include evolution of mites and other arachnids, mites in soil and water, mites on plants and animals, sperm transfer and reproduction, mites and human disease, and mites as models for ecological and evolutionary theories. © Springer Science+Business Media Dordrecht 2013. All rights are reserved.
The use of sugarcane trash (tops and residue) retention systems has been reported to lead to increases in total soil organic carbon (TOC) stocks. However, these increases have generally been small and confined to the top 0.05m of the soil profile. It has been hypothesised that the amount of TOC sequestered could be increased if the intensive tillage that occurs at the end of a sugarcane ratoon cycle, which is known to decrease TOC, could be eliminated. This research examined the effect of no-till management and/or trash retention on four trial sites throughout Queensland, to assess the ability of this management to increase TOC stocks. Management effects on particulate organic carbon (POC), humus organic carbon (HOC), and resistant organic carbon (ROC) stocks were also assessed using mid-infrared spectroscopy. No significant changes in TOC, POC, HOC, or ROC were observed over either 0-0.1 or 0-0.3m depth at any of the sites examined, when sites were considered as a whole. The results indicate that these management practices currently have limited capacity to increase TOC stocks on these soil types over 0-0.1 or 0-0.3m depth for the purposes of carbon sequestration.