Profitability of precision phosphorus application on a commercial farm in the Heidelberg district, Western Cape

English: Phosphorus (P) is an important nutrient required by every living plant and animal cell, and deficiencies in soils could cause a restriction on crop production. P is also a primary nutrient essential for root development and crop production, and are needed in the tissues of a plant where cells rapidly divide and enlarge. Precision agriculture (PA) could assist the farmer in applying the prescribed amount of P to the part of the field where it is required. Variable rate technology (VRT) is therefore a tool that can help with the development of strategies for phosphate fertiliser management. The main objective of this research is to determine the effect of precision P application on the profitability of PA on a commercial farm in the Heidelberg district in the Western Cape Province in South Africa. The study was conducted in collaboration with Mr Gildenhuys (on-farm trials) in the Heidelberg district in the Western Cape, South Africa. Four fields, totalling 106 ha, were identified as research fields for the study. The main crops included in the study were wheat, canola and barley (third year). As many as five soil types were found in each field, which was divided into two halves. One half was planted by making use of VRT, and the other half was planted by conforming to the traditional farm management system or single rate (SR). The same crop was planted on both halves. Wheat, canola and barley were used in a crop rotation system. The specific objectives were to determine the winter grain response to P on different soil types, the relationship with and effect of previous and current years’ yields on the following year’s P application and whether spatial econometric models are more accurate than traditional ordinary least squares (OLS) models in predicting the profitability impact of P on PA. The results obtained show significant differences between OLS, spatial error (SER) and restricted maximum-likelihood (REML) models. All the measures of goodness of fit indicated an increase in fit from the OLS to the SER model, with the best fit being achieved with the REML model, implying that the use of this model resulted in more accurate estimates. Profit analysis based on the application of statistical models indicates that, on average, the VRT treatment resulted in higher profits than the SR treatment. It could not be established, based on this study, that yield response to fertiliser depends on a specific soil type, because some soil types delivered higher yields and profits during certain years and during others they performed considerably weaker. It can thus be concluded that yield responses and profits differ from year to year and also within the crop rotation system (wheat, canola and barley). From the conclusions generated in hypothesis testing it is evident that the wheat crop yield response to P varied according to soil type. Over a three-year period, the VRT application of P lead to higher profitability compared to the SR application of P.