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 sus ceptible to leaching losses. Thus, our greatest potential for controll ing leaching losses of agrochemicals is through the management of thes e compounds in the surface soil. A variety of strategies have been emp loyed to maximize the residence time of applied chemical in the surfac e soil, including: timing of application, formulation (e.g., slow-rele ase fertilizers and encapsulated pesticides), and the use of compounds that modify microbial activity in soil (e.g., nitrification inhibitor s). Although these strategies have met with some success, more precise quantification of the microbial transformations of agrochemicals is r equired to aid the development of improved management strategies. The high spatial variability exhibited by many microbial processes, in man y cases, precludes precise quantification. A greater understanding of the factors contributing to the variability of microbial processes all ows for improved estimation, as well as for the assessment of key driv ing variables controlling microbial processes in soil. This article re views several aspects of spatial variability associated with microbial populations and processes. The discussion focuses on the scale at whi ch 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 final ly, some statistical considerations for characterizing variability are presented.