Abstract

This study aimed at assessing the effects of phosphorus (P) rates on the growth and yield of three soybean cultivars in Vhembe district, Limpopo Province, South Africa. Field experiments were carried out at the University of Venda’s experimental farm, Thohoyandou over two seasons (season I: February – May 2006; season II: November 2006 – March 2007). The experiments consisted of a factorial combination of P fertilizer rates (0, 30 and 60 kg P ha^-1) and soybean cultivars (Pan 520RR, Highveld Top, and LS 555) arranged in a randomized complete block design and replicated three times. Crop biomass (three stages: vegetative phase, 50% flowering and harvest maturity) and grain yield were determined. The (Agricultural Production Systems Simulator) APSIM model (version 5.3) was used to simulate crop biomass and grain yield and to assess the long-term risks associated with yield production of soybean crop. P did not affect crop biomass at harvest maturity but the effect of cultivar was significant (P = 0.01); LS 555 had lower grain yield (701 kg ha^-1) compared with Pan 520RR (1457 kg ha^-1) and Highveld Top (1241 kg ha^-1). There was a strong positive relationship (R² = 0.97) between observed and predicted grain yield data but the predicted yields were generally lower than the observed values. These preliminary findings show firstly, that the addition of P may not affect grain yield of soybean in this area, secondly, that Pan 520RR and Highveld Top may be suitable for cultivation in this area, and lastly, that APSIM model may be a useful tool in predicting soybean productivity in this area.

Key words: P application, cultivar, crop biomass, grain yield, APSIM simulation.