Interaction of Organic Matter with Soil Microfauna

Essay

Soil organic matter is significant in many physical, biological and chemical processes due to its influence on the water holding capacity, cation exchange capacity, soil structure, its ability to develop complexes with metal ions, as well as a nutrient source and store. Organic matter in the soil is also associated with promoting favorable infiltration and permeability. Organic matter is very stable and does not decompose readily. Organic matter maintains itself at a high level, even after repeated cultivation of the soil. There are very complex processes involving soil organic matter dynamics as on one side; vegetation influences soil formation through the generation of organic components in the form of litter, roots, crop residues, and exudates. On the other hand, the soil properties co-determined by the soil organic matter content influence the vegetation growth. The interactions of microorganisms with the soil micro- and macrofauna are essential in the formation and decomposition of soil organic matter. Soil fauna improves the fragmentation of coarse particulate matter into finer fractions and affects the distribution of organic matter in the soil. The soil fauna is categorized into three groups depending on their size and their adaptation to living in either the air-filled pore space of soil and litter or the water-filled pore space. One of the groups is the microfauna, which is small (less that 0.22 mm body width on average) and live in water-filled pore space.

Examples of microfauna are protozoa and nematodes. The second category is the mesofauna, which is an average size of 0.2 -2 mm and lives in the air filled pore space of soil and litter. They include microarthropods (primarily mites (acarids)) and springtails (collembolans) and the small Oligochaeta, the enchytraeid ae. The third group of soil fauna is the macrofauna, which is larger than 2 mm in size and includes earthworms, termites and large anthropoids (Fonseca, 2011). The macrofauna can dig the soil and are sometimes known as the “ecosystem engineers” due to their large impact on soil structure. The different groups of soil fauna have diverse activities in the soil that are related to their size. The soil microfauna has a limited ability to alter the soil structure whereas the soil mesofauna, which is larger, have a greater capacity to influence the soil processes that are involved in the formation of soil aggregates. The soil macrofauna redistributes organic residues in the ground as well as expose a greater surface area for microbial decomposition and affect the macropore structure and facilitate water infiltration. The soil mesofauna regulates the microfaunal and fungal populations and also contribute to the fragmentation of organic residues. The feeding activities of the soil fauna have also been found to regulate soil microbial community structure and abundance (Varma & Sharma, 2017).

The soil microfauna feeds on microflora, other microfauna, plant roots, and sometimes larger organisms (such as entomopathogenic nematodes that feed on insects and other larger invertebrates). The population dynamics of the soil microfauna often fluctuates dramatically in response to food availability as well as to wetting and drying cycles in soil.

The soil biological fertility, a factor that contributes to soil health is defined as the capacity of microorganisms living in the soil to contribute to nutritional needs of the plant and foraging animals and at the same time maintaining the biological processes that positively contribute to the physical and chemical soil state. Soil biological fertility is an important component of agricultural systems as it influences nutrient uptake by plants in association with mycorrhiza, soil structure in parallel with chemical and physical soil properties and nutrient release from organic matter during its decomposition. Improving the soil biological fertility provides significant benefits to agricultural soils due to its interconnection with soil chemical and soil physical fertility. Besides, the focus on enhancing healthy soil conditions for plant growth with diverse microbial communities is associated with plants that are more resilient to disease. Nutrient inputs from mineralization of soil organic matter can also result in the increase of resilience of crops to insect pests through biological processes that provide plants with potentially more balanced nutrition especially through moderation of high levels of fertilizer N that enhances the susceptibility to foliar pests.

The interaction of soil fauna, microorganisms, roots and organic matter is linked with contributing to soil aggregation formation as well as stabilization. Soil particles aggregation physically protects soil organic matter and also changes the structure of the soil microbial community by mediating the flow of oxygen and water; hence further influencing the soil organic matter dynamics and nutrient cycling.

Although the soil microbial biomass -comprising primarily of fungi, soil microfauna, bacteria, and algae – accounts for only 1 - 3 percent of the organic C and 2 to 6 percent of the organic N in the soil, it is crucial in soil organic matter dynamics. Soil microbial biomass is responsible for controlling the transformation in the soil and influences C storage as well as is both a sink (during immobilization) and temporary source (during mineralization) of plant nutrients (Gregorich & Carter, 1997). The diverse metabolic functions of soil microorganisms, especially bacteria, regulate the nutrient cycling and energy that occurs in the soil and is significant in the global cycling of a wide variety of inorganic compounds, particularly nitrogen, sulfur, and phosphorus. The processes of nutrient cycling and the accumulation of organic matter, which are made possible by microorganisms, affect soil formation. The soil fauna, which comprises of soil micro-organisms and the larger animals within the soil such as centipedes, worms, and grubs, have an impact on the soil formation through breaking down organic matter as well as the incorporation of organic matter into the soil. The larger animals mix and aerate the soil as well as incorporate organic matter into the soil through digging and burrowing. The soil microfauna facilitates the decay of organic matter and is also crucial for the formation of a dark surface layer. Although the primary processors of the dead plant materials that remain on the soil surface are termites and other macroinvertebrates, the decomposition of litter and roots that are buried in the ground takes place through the interactions of a complex soil microfauna and mesofauna and the microflora. The decomposition of plant residues is carried out by bacteria and fungi, in which they break them down and hold the nutrients in their bodies, glued and bound to soil particles. This activity, however, prevents the nutrients from leaching out into the soil; thus, the nutrients are not available to the plants at this point. The bacteria and fungi hold onto these nutrients until nematodes, small microarthropods, protozoa, and earthworms consume the individuals of fungi and bacteria and release the nutrients in forms that are available to plants (Ganguly, 2014).

The soil microfauna is also responsible for the regulation of bacterial and fungal population. The regulation of bacterial and fungal population, as well as the altering of nutrient turnover in the soil, may influence the aggregate soil structure through interactions with microflora (Chesworth, 2008).

Soil microfauna and microflora are also crucial in nitrogen cycling in the soil (Follett & Hatfield, 2001). The release of nitrogen from plant and animal residue is dependent on microbial activity. Soil bacteria use the more readily available, soluble or degradable organic fractions. Fungi, as well as actinomycetes, decompose the resistant cellulose, lignin, and hemicellulose. At all times, the soil microbial biomass contains a lot of the actively cycling nitrogen of the soil and represents a relatively available nitrogen pool capable of rapid turnover. The energy flux through the soil microbial biomass (SMB) drives the decomposition of organic residues and soil organic matter. Plant root biomass and soil microbial processes are intimately associated with the grassland systems. Grasses have a large and finely fibrous root system that gets well distributed through the upper part of the soil. Soil microfauna that decomposes the highly carbonaceous grass roots secretes a substance that assists in the improvement of the soil structure, to bind the soil particles and hence control erosion. If the decay exceeds carbon inputs, the soil organic matter will decline. The resulting mineralization of nitrogen and other nutrients will lead to their becoming vulnerable to potential losses into the environment by denitrification, leaching or other mechanisms.

The soil microfauna plays crucial roles in organic matter that include the release of available nutrients, accretion as well as loss of soil organic carbon and bioremediation of contaminated soils. The interaction of the soil microfauna with organic matter is also significant because it facilitates decay of organic matter and the formation of a dark surface layer.

References

Chesworth, W. (Ed.). (2008). Encyclopedia of soil science.

Follett, R. F., & Hatfield, J. L. (2001). Nitrogen in the environment: sources, problems, and management. The Scientific World Journal, 1, 920-926.

Fonseca, M. J. (2011). Soil microbiology and sustainable crop production.

Ganguly, S. (2014). Role of soil microfauna and microflora in agriculture. International Journal of Agricultural Sciences, 10(1), 477-478.

Gregorich, E. G., & Carter, M. R. (Eds.). (1997). Soil quality for crop production and ecosystem health (Vol. 25). Elsevier.

Varma, A., & Sharma, A. K. (2017). Modern Tools and Techniques to Understand Microbes.

Carolyn Morgan is the author of this paper. A senior editor at MeldaResearch.Com in research paper writing services if you need a similar paper you can place your order from Top American Writing Services.