Impact of variable-rate application of nitrogen on yield and profit: a case study from South Africa

Abstract

The response of maize (Zea mays) to banded variable-rate nitrogen (N) application over a period of 3 years (2002/3-2004/5) is analyzed. The experimental design alternated variable-rate (VR) and single-rate (SR) applications of N. The yield monitor data were spatially autocorrelated and therefore were analyzed with spatial regression methods. The baseline spatial regression model defined in this study showed that the VR treatment, treatment by year and treatment by management zone were statistically sig- nificant. Sensitivity tests were applied; the first showed that VR treatment had a yield advantage when soil depth was greater than the field average of 174 cm. The second test showed that the VR N rates applied were close to those that would maximize profit. Partial budgeting indicates that benefits from VR vary from year to year, but in this test VR was slightly more profitable than uniform rate application. Economic sensitivity testing indi- cates that farm size and the price of maize are the key factors in the profitability of VR N.