Response of soybean (glycine max l.) To application of inorganic fertilizers, cattle manure and lime in western Kenya
Soybean production in Kenya has remained low, partly due to soil nutrient depletion and degradation which have been considered serious threats to agricultural productivity. Studies have shown that productivity of soils in western Kenya is limited by deficiency of nutrients such as nitrogen, phosphorous and potassium a problem compounded by low organic matter and soil acidity. Responses of soybean to nitrogen and phosphorous have been studied and documented but little has been done on micronutrients, and also to establish the scale of macro and micronutrient deficiencies and soybean yield response to a combination of organic and inorganic fertilizers. Despite the major opportunities that soybean provide to human nutrition, household income and soil N budgets in Africa, their contribution has been curtailed by several factors including low priority given to proper nutrient management. This is because grain legumes, soybean included, have been promoted as crops that require no fertilizer application. The objective of the study was to evaluate the effect of inorganic fertilizer, cattle manure and lime on the growth and yield of soybean in nutrient omission trials. Field experiments were conducted in four sites (Eshirali, Masaba, Nyabeda and Eshisa) during the 2012 cropping seasons in Western Kenya to determine the effect of inorganic fertilizers, cattle manure and lime on nodulation and yield of soybean (Glycine max L.). The experiment was laid out in a randomized complete block design with three replicates. The treatments consisted of: 1) Control-without inoculant and fertilizer; 2) Inoculation alone; 3) NPK; 4) PK; 5) NP; 6) NK; 7) NPKSCaMgZnMo and 8) NPKSCaMgZnMo+Manure+Lime (Seeds were inoculated with rhizobia inoculant containing USDA-110 Rhizobium strain). Inorganic fertilizers were applied at rates of 20 kg/ha N, 30 kg/ha P, 60 kg/ha K, 23 kg/ha S, 20 kg/ha Ca, 5 kg/ha Mg, 3 kg/ha Zn, 3 kg/ha Mo, 10 tons/ha manure and 5 tons/ha lime. Soybean variety SB-132 was used in the trials during both the short and long xvi rainy seasons. Above ground biomass, nodule number, nodule dry weight, nodule mean score, plant height, pod number, final grain yield, stover yield and 100-seed weight were determined. Analysis of variance showed significant site, treatment and site × treatment interaction effects on soybean above ground biomass, nodule mean score, number of nodules per plant, nodule dry weight, plant height, number of pods per plant, 100-grain weight, grain yield and total stover yield in both cropping seasons indicating that treatment effects were site specific. Inoculation alone significantly increased soybean nodule mean score, nodule number and nodule dry weight relative to control in both seasons. Application of NK had significantly lower values in most of the studied parameters than NPK, NP and PK applications. Overall, significantly higher values were noted in NPKSCaMgZnMo+Manure+Lime than in all the other treatments in most parameters. Eshisa site recorded significantly higher values than all other sites in all parameters except 100-grain weight and stover yield in the second season. The findings suggest that combination of inorganic fertilizers, cattle manure and lime would be a feasible option for maximizing soybean yields in western Kenya hence providing an entry point for more research on proper nutrient management to boost soybean production in the region.