Soil chemical analytical accuracy and costs: implications from precision agriculture

Summary. This article reviews soil sampling and soil chemical analysis, discussing their implications from, and applications in, precision agriculture. The variability of a number of agriculturally important soil chemical properties was investigated and the ‘nugget’ variance or effect discussed in terms of its importance in determining the proportion of not only short-range spatial variation, but also sampling and measurement error. Comments were then made on the accuracy of laboratory methods. Analytical variances were compared with world-average and estimated nugget variances for a field in New South Wales, the comparison showing that analytical precision needs to be maintained or improved when developing or adapting analytical methods for precision agriculture. A simple cost-analysis showed that soil chemical analytical costs are much too large for economic use in precision agriculture, costs in Australia being higher than in the United States. The conclusion this paper draws is that, for large-scale implementation of precision agriculture, the development of field-deployed, ‘on-the-go’ proximal soil sensing systems and scanners is tremendously important. These sensing systems or scanners should aim to overcome current problems of high cost, labour, time and to some extent, imprecision of soil sampling and analysis to more efficiently and accurately represent the spatial variability of the measured properties.