SPATIAL VARIABILITY OF MICROBIAL PROCESSES IN SOIL - A REVIEW

Microbial transformations of fertilizers and pesticides in the surface soil have a direct impact on the mass of the agrochemical that is susceptible to leaching losses. Thus, our greatest potential for controlling leaching losses of agrochemicals is through the management of these compounds in the surface soil. A variety of strategies have been employed to maximize the residence time of applied chemical in the surface soil, including: timing of application, formulation (e.g., slow-release fertilizers and encapsulated pesticides), and the use of compounds that modify microbial activity in soil (e.g., nitrification inhibitors). Although these strategies have met with some success, more precise quantification of the microbial transformations of agrochemicals is required to aid the development of improved management strategies. The high spatial variability exhibited by many microbial processes, in many cases, precludes precise quantification. A greater understanding of the factors contributing to the variability of microbial processes allows for improved estimation, as well as for the assessment of key driving variables controlling microbial processes in soil. This article reviews several aspects of spatial variability associated with microbial populations and processes. The discussion focuses on the scale at which variability is expressed, and the soil and environmental variables that serve to control variability at each scale. implications for the development of new management strategies are also discussed, and finally, some statistical considerations for characterizing variability are presented.