Impact of fauna on chemical transformations in soil

Abstract

Agricultural soils contain a multitude of animals. Tiny single celled protozoa to animals several orders of magnitude larger than protozoa thrive in agricultural soils. These communities exist irrespective of management practice or biogeographical location. Soil zoologists are faced with the challenge of understanding how this complex community impacts upon the processes vital for sustainable agricultural production. There is considerable evidence that soil fauna have large impacts on soil chemical transformations. There is also good understanding of the effects of management practices on soil faunal community structure. This should allow reasonable predictions of soil fauna responses to changes in management to be made. However, information on soil fauna effects on soil chemical transformations is not aligned with information on the effect of management practices on soil fauna. Consequently, few clear recommendations can be made to land managers on how they can exploit this resource to improve sustainability from a soil chemical fertility perspective. This chapter examines the impact of fauna on chemical transformations using an ecological framework which considers functional groups, abundance, relative abundance, and species richness of the soil fauna. Functional groups are considered as broad categories of soil fauna (e.g. bacterial feeding nematodes), relative abundance as the relative proportions of individuals from different species or groups, and species richness as the number of species within a functional group. This framework is used to establish principles for interpreting the consequences of changes in soil faunal communities following changes in management practices. Beare (1997) concluded that it was important to determine how differences in soil food web structure can be used to predict the sustainability of agricultural practices. The framework adopted here is an attempt to address this issue. The chapter focuses on the impact of soil fauna on carbon (C) and nitrogen (N) mineralisation as these are two important elements in agriculture which have received a large amount of attention in soil fauna studies. These two elements are integrally linked such that C mineralisation rates are positively correlated with gross N immobilisation (Recous et al. 1999). Nitrogen mineralisation rates can also be dependent upon C:N ratios of the organic matter, although other factors, such as polyphenol and lignin content are also important (Heal et al. 1997). Other elements are obviously important for agricultural production and soil fauna are known to impact upon the way that they are cycled in soil (Seastedt 1984) but these interactions are not considered here. This chapter subsequently addresses the effect of management practices on the soil fauna using the same framework in an attempt to draw out the principles established in the first section. Finally there is a discussion of how soil fauna may be more fully exploited to enhance soil chemical fertility and identifies some potential areas for future research are identified. © 2007 Springer.