Soil tillage resistance as a tool to map soil type differences

Precision agriculture is based on spatial knowledge of soil and crop conditions in the management decisions. In this paper, a method to improve determination of soil physical properties is proposed. Current practice is to analyse soil samples, taken at several locations in a field, for physical properties. To obtain a sound coverage, many soil samples have to be analysed. When soil properties are correlated, it is possible to reduce the number of soil samples of one property and enhance its spatial resolution with the information of another, more densely sampled, property. In this study, information gathered automatically during the major soil tillage operation, ploughing, is used to improve the spatial resolution of sampled topsoil clay content. Plough draught was measured during two seasons on a 6 ha field. The specific plough draught varied between 30 and 50 kNm(-2). Clay content varied between 6 and 22% and topsoil moisture content range was 120-240g kg(-1) during the first year and 180-300g kg(-1) in the second year. The specific plough draught maps of both years showed a similar spatial pattern with a cross correlation coefficient at zero distance of 0.6. The use of specific plough draught as co-variable in the co-kriging technique made it possible to decrease the number of topsoil clay content samples from 60 to 18 ha(-1) with only 20% increase in prediction error. On this field, the spatial variation in top soil clay content was correlated with the spatial variation of the crop yield. (C) 2001 Silsoe Research Institute.