Response of improved soybean varieties to different phosphorus rates
Ahangaana, Julius Peter
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In Uganda, soybean varieties, Maksoy 1N, 2N, 3N, 4N, 5N, and lately 6N were bred to address yield and disease resistance gaps. These varieties have become popular among commercial and smallholder farmers. Unfortunately, their yield potential has never been realized owing to among other things abiotic stresses, in particular phosphorus deficiency. The objectives of this study were to determine (a) Optimum application rates of phosphorus for Maksoy varieties; (b) Response of seed protein and oil content of Maksoy varieties to various P application rates; and (c) Phosphorus use efficiency for the different Maksoy soybean varieties. The study was conducted in central Uganda, specifically at the Makerere University Agricultural Research Institute, Kabanyolo (MUARIK) in 2017-2018. The experiment was laid out in a completely randomized block design, arranged with split-plots, and three replications. Phosphorous fertilizer TSP (0:46:0) was the source of P. Parameters assessed included plant height, number of leaves and branches, grain, grain-protein and oil contents, phosphorus use efficiency (PUE) and phosphorus apparent recovery. There was a significant ((P ≤ 0.001)) interaction between variety and P rates, whereby a rise in P rates increased the number of leaves, branches and plant height. Application of P also increased the number of pods per plant, grain yield, protein and oil content across Maksoy varieties. The most grain yield gains (1078 and 1384 kg ha-1) were recorded with Maksoy 4N representing 63.49 and 81.51% at 30 and 60 kg P ha-1 respectively, and the least (307 and 554 kg ha-1) in Maksoy 1N. However, Maksoy 1N had the highest grain-protein content, while Maksoy 3N yielded the highest amount of grain-oil content. Maksoy 2N was the best in recovering and using available P efficiently. Phosphorus applied at 30 kg ha-1 was the optimum for maximum grain yield of these varieties. Maksoy 3N which was the most P tolerant variety could be an ideal candidate for growing in areas that are mostly P deficient. In terms of yield qualities, it is clear that Maksoy 4N yields highest grain, Maksoy 3N for seed oil content and Maksoy 1N for seed protein when supplied with the most P on the study soil.