The delta yield procedure for nitrogen fertilisation of maize in South Africa

Abstract

The nitrogen fertilisation requirement for maize in South Africa is generaly estimated through the optimum yield-nitrogen rate procedure. The efficacy of this procedure is questionable. Delta yield, the difference between the maize grain yield at the economic optimum and that of a zero nitrogen fertilised control, was investigated for its ability to estimate the economically optimum nitrogen fertilisation rate for the South African maize producing area. Data from 124 locality-year fertilisation trials scattered over this area were used for the analyses. As in North America, optimum nitrogen rate correlated better with delta yield (R² = 0.66) than with optimum yield (R² = 0.51). Consequently, it shows potential to be a trustworthier predictor of the nitrogen fertilisation requirement of maize than the traditional optimum yield-nitrogen rate procedure. The delta yield model (Y = X^0.602 where Y is the amount of fertiliser nitrogen and X delta yield, both measured in kg ha⁻¹) was not only uniform for different soil and climatic regions in South Africa, but appears to be similar to that found for five states of the USA.