Summary
Soil biology research is often organism-based and less focused on the community interactions and the dynamics of soil biota populations. The organism-based approach to soil biology research has provided knowledge about soil biological diversity and role of specific soil biota in particular soil processes. However, biological functions at the plant production level under field conditions are mediated by diverse types of organisms and interactions between various levels of the soil food web. Since the plant is the major source of available carbon for biological activity, especially in low fertility Australian soils, research on soil biota should consider the quality and quantity of carbon inputs from plants (through exudation and above- & below ground plant residues) and plant-induced changes in soil physical and chemical properties. Also, unlike cropping systems, pastures are composed of mixtures of plant types (legumes, grasses, C3, C4).
The availability of carbon in pasture systems is mediated strongly by grazing management through above-and below-ground plant growth in response to grazing. Therefore, the development of options to manage soil biota should consider pasture composition and carbon inputs mediated through grazing management, in addition to soil organic matter. Where and when are the resources and conditions favourable for soil biological activity? Soil physical and chemical conditions regulate soil biological processes and the distribution of biota in soil is heterogeneous, i.e. concentrated at few microsites. Even though the influence of soil moisture and temperature on biological processes is known, reliable estimations of biological functions in pastures in the field have been difficult to achieve due to the variation of the soil environment in space and time. In the majority of dry land cropping regions in southern Australia, moisture availability plays a critical role in determining the activity of both microflora and soil fauna. Temporal patchiness in favourable soil and environmental conditions, determine the actual contribution of plant-specific biological functions for crop productivity and soil health.
Such information would allow more accurate estimates of the likely contribution of soil biological activity to pasture production and environmental health in field situations. Soil structural aspects such as habitable pore space and the physical distribution of microsites rich in biota) and variation in moisture and temperature (hence also oxygen) need to be considered in placing soil biological research into the field context. By considering the interactions between the three main components of a pasture system, i.e. plant production (plant type and grazing management), environment (soil and climatic) and soil biota (populations of functional groups and activity), research should provide information on how the regulating factors affect biota dynamics and activity in a field context (Appendix 8).
This approach to research should in turn lead to development of management options related to grazing, rotations, system inputs to best utilize beneficial soil biological activity and minimize losses, e.g. due to disease and negative environmental impacts. Pasture production is supported and enhanced by soil biological processes. There are likely to be substantial opportunities to increase pasture production towards the potential production target based on water use efficiency. Research on soil biology in pastures should focus on removing constraints to production and increasing input (water and nutrient) use efficiency. Using this approach, yields in cropping systems have increased substantially towards the potential, based on water use, over a period of 20 years. Research on biological components and interactions in a farming systems context, using potential plant production as a benchmark, has the potential to substantially improve pasture production and sustainability.
