Tools for optimizing management of spatially-variable fields

Efficient use of agro-chemicals is beneficial for farmers as well as for th e environment. Spatial and temporal optimization of farm management will in crease productivity or reduce the amount of agro-chemicals. This type of ma nagement is referred to as Precision Agriculture, Traditional management im plicitly considers any field to be a homogeneous unit for management: ferti lization, tillage and crop protection measures, for example, are not varied within a single field. The question for management is what to do it-hen. B ecause of the variability within the field, this implies inefficient use of resources. Precision agriculture defines different management practices to be applied within single, variable fields, potentially reducing costs and limiting adverse environmental side effects. The question is not only what and it-hen but also where. Many tools for management and analysis of spatia l variable fields have been developed. In this paper, tools for managing sp atial variability are demonstrated in combination with tools to optimize ma nagement in environmental and economic terms. The tools are illustrated on five case studies ranging from (1) a low technology approach using particip atory mapping to derive fertilizer recommendations for resource-poor farmer s in Embu, Kenya, (2) an example of backward modelling to analyze fertilize r applications and restrict nitrogen losses to the groundwater in the Wieri ngermeer in The Netherlands, (3) a low-tech approach of precision agricultu re, developed for a banana plantation in Costa Rica to achieve higher input use efficiency and insight in spatial and temporal variation, (4) a high-t ech, forward modelling approach to derive fertilizer recommendations for ma nagement units in Zuidland in The Netherlands, and (5) a high-tech, backwar d modelling approach to detect the relative effects of several stress facto rs on soybean yield. (C) 2001 Elsevier Science Ltd. All rights reserved.