Verwantskap tussen anorganiese grondstikstof en mielie-opbrengs met beheerde verkeer

English: Nitrogen fertilizer recommendations for maize production in South Africa are based on yield to be achieved. Inorganic soil nitrogen is seldom used. This approach causes difficulties in the meaningful seasonal adoption in application rates to be made due to variance in inorganic soil nitrogen due to climatic variations such as too much rain or drought. Therefore the relationship between inorganic soil nitrogen and inorganic soil nitrogen with maize yield under controlled traffic practices was carried out. Data of fertilizer trials at Viljoenskroon on a Clovelly soil (1993/94 to 1997/98) and at Heidelberg on a Avalon soil (1991/92 to 1997/98) were used to determine the relationship between applied nitrogen and maize yield, applied nitrogen and inorganic soil nitrogen as well as inorganic soil nitrogen and maize yield. At both localities the nitrogen rates were factorially combined with phosphor rates and replicated three times in a "roosterontwerp". The grain yield was determined annually at both localities. Soil samples were annually taken from two weeks after nitrogen side dressing in a 300 mm band over the maize row (intra row samples) and before plant in a 1200 mm band between the maize rows (inter row samples) on each plot at both localities. These samples were analysed to determine the amount of inorganic nitrogen in the row as well as total soil volumes. The relationship between applied nitrogen and grain yield was parabolic, between applied nitrogen and inorganic soil nitrogen quadratic and between inorganic soil nitrogen and grain yield parabolic. These relationships had explained more variance at Viljoenskroon than at Heidelberg throughout the study. According to the variance, the relationship of soil reaction on nitrogen application predicted by both localities over years was reliable. Plant reaction was predicted at by both localities over years by the relationship between soil nitrogen in the intra row maize rows and relative yield. According to this nitrogen application recommendations can be made for the optimum amount of soil nitrogen in the intra row for a certain relative maize yield. The amount of nitrogen required to raise inorganic nitrogen content of intra row soil to the desirable level was obtained by the use of the regression equation. The general practice for maize production in South Africa is that a third of the nitrogen is band placed at planting and the remainder applied four to six weeks after planting as top dressing. The abovementioned information could help the farmer to calculate the amount of nitrogen that should be applied to adjust inorganic soil nitrogen levels before and/or during a specified season. This approach has the advantage that where the maize yield varies according to inconsistent rainfall nitrogen applications may be adjusted. It must be accentuated that this approach puts greater demands to farmers, soil annalistic laboratories and fertilizer providers. Over- and under fertilization should considerable decreased due to this approach. More research is however needed for exploitation in other ecotypes.