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The soil food web with various indicators of soil health overlaid (black boxes). 

The soil food web with various indicators of soil health overlaid (black boxes). 

Source publication
Conference Paper
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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...

Contexts in source publication

Context 1
... 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). ...
Context 2
... 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. ...

Citations

... 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). ...
Article
Full-text available
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.
... Organic carbon has a key function for soil structural integrity (Kay, 2018), soil fertility (Herrick & Wander, 2018), water retention and availability (Eden et al., 2017), soil biological health (Brackin et al., 2017;Lehman et al., 2015), reducing uptake of contaminants (e.g., cadmium) by crops (Prokop et al., 2003;Q. Wang et al., 2014) and pH-neutralising effects in acidic soils (Qi et al., 2018). ...
... 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. ...
... 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: ...
Article
Full-text available
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.
... 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. ...
Chapter
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.
... 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? ...
... 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). ...
Article
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. ...
Article
Full-text available
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.
Article
Full-text available
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.