Site specific crop management adapts the fertilizer amount applied in relation to the intra field crop needs. In this context, tries were carried out under field conditions. The aim of the trials was to develop technico-economic baseline data and methodology of soil sampling for precision agriculture in Upper-Normandy.

The objective was to define a method to characterize the intra field yield variability concerning rates of phosphorus and potassium. The intra field variability of these two rates is essentially due to the past history of the field (regrouping of plots) and the past addition of fertilizer.

The trials were carried out in one field. In this field a grid sampling of soil was taken in order to established maps showing rates of P₂O₅ and K₂O. For each rate we calculated the quantities of fertilizer required using the COMIFER method. Techniques of electric conductivity and resistivity were used to establish the intra field heterogeneous characteristics. Yield maps were made for each field

The first step was to characterize the rates of P₂O₅ and K₂O with relation to the past history of the fields plots. Then for this field we calculated, using geostatistic technics, the minimal number of soil analyses required par hectare to correctly describe the heterogeneity of the rates. Finally we evaluated the economic consequences of the use of site-specific applications applied to commercial farms in terms of the reduction of the use of fertilizers.

So, the geostatistic analysis allows us to evaluate the heterogeneity of the P₂O₅ and K₂O rates and to define the number of analyses per hectare necessary two samples per hectare in our experimental conditions We were able to assess the potential reduction of P and K fertilizer as well as the environmental and economic gains of this technic. The results have shown economic and environmental gains from these techniques in our pedoclimatic conditions.