What is soil biological fertility?

Abstract

There is increasing interest in soil management practices that enhance biological contributions to soil fertility due to greater awareness of the need for sustainable farming systems (e.g. Lynam and Herdt 1989, Dick 1992, Roper and Gupta 1995, Doran et al. 1996, Swift 1997, Condron et al. 2000, Mäder et al. 2002, von Lützow et al. 2002). This has occurred due to the requirement for better fertiliser use efficiency which is essential in: i) developing nations where cost and availability constrain production (Swift 1997) and ii) many developed nations where public concern over environmental pollution from agricultural sources and associated government legislation restricts gaseous losses and nutrient leaching (e.g. N: Hatch et al. 2002, P: Leinweber et al. 2002). There has been a considerable decline in soil organic matter levels and associated loss of soil structure in many intensively cropped soils throughout the world. This has caused scientists and landowners to consider more carefully how various components of the farming system can be managed to more efficiently benefit from biological processes that improve soil fertility. Soil biological processes are extremely diverse and complex (Lavelle and Spain 2001). Physical and chemical soil characteristics, climate, plant communities and agricultural practices influence soil biology in a magnitude of ways, with both positive and negative influences on the overall fertility of soil. This level of complexity constrains our ability to assess or predict the biological state of soil through measures of abundance of organisms or their activity (Pankhurst et al. 1997). The current inability to predict the outcome of a change in agricultural management on soil biological processes, with a subsequent understanding of what this means in terms of production or the environment, is a major constraint to the successful design of farming systems that harness the biological potential of soil. Many studies have attempted to define the biological status of soil using simple indicator measurements (Doran and Parkin 1994, Gregorich et al. 1994, Franzluebbers et al. 1995, Pankhurst et al. 1995, Walker and Reuter 1996, Stenberg 1999). Whilst this is appealing to scientists, land holders and policy makers, it is extremely difficult to find correlations between potential indicators and crop production, long-term sustainability and environmental impact. Part of this difficulty has been with understanding how organisms and the functions that they perform interact with chemical and physical soil attributes in agricultural soils to regulate crop production and influence the longer-term status of the soil resource. Due to spatial and temporal heterogeneity and the enormous diversity displayed in soil biological characteristics, it is not easy to use them to define 'best practice' for land management. The focus of this book is thus to provide an overview of a range of biological processes that contribute to soil fertility and to discuss the manner in which management practices influence soil biological fertility. With the complexity of these biological processes in mind, the impact of major management options and farming systems on soil biological processes can be addressed. The consequence of this is the basis for sustainable use of the whole soil resource, which demands equal consideration of biological, physical and chemical contributions to soil fertility. Inclusion of information about soil biological fertility in farm management decision-making should allow more precision in selecting inputs that complement the capacity of a soil to sustain production and minimise environmental damage such as might be caused by nutrient loss. If the type of production at a site is changed, different biological, physical and chemical states might be required to sustain the soil resource there, depending on the production system in place. A set of biological characteristics necessary for sustaining the soil resource at a particular site cannot be prescribed because different farming systems, or even different stages in the same farming system, might require differences in soil biological fertility. Therefore, a suite of soil biological characteristics needs to be defined for each land use category according to the soil type and climatic conditions. © 2007 Springer.