SITE-SPECIFIC MANAGEMENT - BALANCING PRODUCTION AND ENVIRONMENTAL REQUIREMENTS AT FARM-LEVEL

Spatial variability of soil conditions and potato growth were studied in a 6 ha field in a Dutch polder. Potato yields, measured in 65 small plots, varied between 30 and 45 tons/ha, while yields of commercially attractive large potatoes varied between 3 and 15 tons/ha. Such diffe rences are economically significant for a farmer. A system for site-sp ecific management is discussed, including site-specific sampling for s oil fertility and use of dynamic simulation modeling to characterize s oil water regimes and nutrient fluxes (e.g. of nitrate). Total N in th e early part of the growing season varied between 21 and 53 kg/ha. Sit e-specific fertilization rates can be based on such values. When compa red with recommended rates obtained from one mixed sample for the enti re field, local over- and under-fertilization can be demonstrated. The se are bound to lead to groundwater pollution and inefficient producti on. Modeling can be used to balance production and environmental aspec ts in a quantitative manner, as is demonstrated in this paper. Data ne eds of the WAVE model, used to simulate yields and nitrate fluxes, are discussed including distinction of four functional layers for the fie ld, which define all variability in basic hydraulic characteristics. T echnical developments in site-specific technology are briefly reviewed . Finely-tuned management practices, including fertilization, appear t o be attractive and practical procedures for more efficient natural re sources use.