AbstractsBiology & Animal Science

Soybean is a vital cash, oil and protein crop. To achieve good yields and quality, adequate amounts of essential nutrients are required. Therefore, application of P and K plus inoculation with Bradyrhizobium bacteria should be included in the general production of soybean. However, the practice in South Africa is to apply no P and K when producing soybean since the farmers rely on residual P and K from the previous cropping season. The objective of this study was to determine that direct P and K application to a soybean crop may have positive results in terms of production and quality. The research was conducted at the Hatfield Experimental Farm of the University of Pretoria under green-house and open field conditions during the 2010/2011 season. The field trial treatments consisted of combinations of 3 levels of P (0, 20 and 40 kg P ha-1) and 3 levels of K (0, 50 and 100 kg K ha-1)applied in factorial combination for a Completely Randomized Block design, replicated four times. The pot trial was also a factorial experiment using a Completely Randomized Design with the two factors each at five levels of application (P at 0, 10, 20, 30 and 40 kg P ha-1 and K at 0, 50, 100, 150 and 200 kg K ha-1). Each treatment combination was replicated four times. Phosphorus and K were applied as Superphosphate (10.5%) and KCl (50%) respectively. The cultivar LS 6161R was planted under rain-fed conditions while LS 6162R was used as test crop in the green-house. Seeds were inoculated at planting with Bradyrhizobium japonicum, with no additional N applied during the season. Composite soil samples were collected from each plot and pot before and after planting and analyzed for pH (H2O) and plant-available nutrients. During the growing season,the field trial plants were sampled for LAI while canopy closure and plant height were measured for plants in the middle rows of each plot. Harvesting commenced after leaves senesced and pods had turned brown. The data recorded was on the number of pods per plant, number of seeds per pod, number of nodes per plant, fresh and dry root, stem and pod mass, 100-seed mass, total seed yield as well as protein and oil content. The results for the field trial showed that K significantly improved plant height, canopy closure and 100-seed mass as compared to the control. The application of P and K revealed no significant impact on leaf area index. Although not significantly, pod number per plant was reduced by applying P, resulting in the control having the highest number of pods. A significant improvement in grain yield was observed through application of K. The highest grain yield (2.60 t ha-1) was observed at the highest K level (100 kg K ha-1). The lowest grain yield was observed where no K fertilizer was applied. Although grain yield was not significantly affected by P nor the P*K interaction, there was a trend of increased yield with increased levels of P and P*K.Phosphorus, irrespective of the application rate, increased protein content but decreased oil content, while…