Soil, Water and Yield Relationships in developing Strategies for the Precision Application of Nitrogen Fertiliser to Winter Barley

To investigate on-farm strategies for the site-specific application of nitrogen fertiliser, two hypotheses were tested: that maximum economic output is either obtained by applying more nitrogen to the historically highest yielding soil and less to the lowest yielding soil, or by the reverse strategy. Field experiments were conducted in 1997, 1998 and 1999 on a commercially managed field of winter barley (Hordeum vulgare), comprising a clay loam and a sandy loam, in Cambridgeshire, UK. The experiments were carried out in a strip-based design using on-farm equipment. In all 3 yr, at typical application rates of 100–200 kg[N] ha−1, there were significant differences between the yield of the clay loam and the sandy loam soil. When rainfall in the February to July period of the growing season was higher than average, the sandy loam soil yielded significantly higher than the clay loam soil and the reverse occurred when the rainfall was lower. Despite the above factors, analysis showed that the maximum of the yield response curve for each soil, occurred at the same application rate in each growing season. Given this relationship, there was no economic benefit from variable rate application of nitrogen to different soil units based upon historic yield, or any other form of information.