SOYBEAN (Glycine max L. Merr.) GROWTH AND YIELD RESPONSE TO INOCULATION, NPK, AND ALTERNATIVE PHOSPHORUS SOURCES

Abstract

Soybean cultivation has failed to achieve its potential yields owing to factors such as inadequate soil fertility, suboptimal nutrient management practices and imbalances in fertilizer application, among other challenges. A study was conducted at Kpalsogu. Tolon district, in the Northern region of Ghana to assess the impact of rhizobium inoculation, two OCP compound fertilizers, TSP, 20-40% substitution of TSP with Rock phosphate and inclusion of trace elements B and Zn on field performance of Favour soybean. The treatments were laid in a split-plot design replicated four times. The main plot factor was Rhizobium inoculation at two levels (inoculation vs no inoculation). The subplot factor was made up of fifteen fertilizer regimes. Generally, parameters associated with plant growth was significantly influenced by the application OCP compound fertilizer treatments NPK(14:18:18+B, Zn) and NPS+TE(14:31:5+B, Zn). Most of the growth and yield parameters were not affected by rhizobium inoculation. The complete substitution of TSP with rock phosphate as a source of phosphorus lagged behind other fertilizer treatments but it was better than untreated control. However, up to 40% substitution of the TSP with rock phosphate did not have any adverse effect. Indeed, 80%TSP+20%RP treatment produced the highest grain yield of 2006 kg ha-1. Partial budget analysis showed that TSP and 80%TSP+20%RP treatments recorded marginal rate of return of 561.4% and 295.1% respectively. Ultimately, the study found the compound fertilizers improved growth and yield with TSP performing better than rock phosphate in terms of P sources. In order to maximize yield and increase profit margins, the study recommends the use of triple superphosphate or 80% TSP in combination with 20% rock phosphate. Further study should be conducted to ascertain if the absence of K in NPS+TE(14:31:5+B, Zn) is the cause of poor nodulation in that treatment.