Rhizobium inoculant integration with organic and mineral fertilizer: Impact on weed infestation, soybean growth and yield in southern Guinea savanna, Nigeria

Abstract

To evaluate the effect of integrating Rhizobium inoculant, organic and inorganic fertilizer on weed infestation, growth and yield of soybean, an on-farm experiment was conducted in the 2015 and 2016 rainy seasons in Paikoro Local Government Area of Niger State, Nigeria. The treatments were control (no input), inoculant (I ) only, I + phosphorus (P), I + P + potassium (K), I + P + K + micronutrients (M), and I + P + K + M + cow dung (CD) replicated three times in a randomized complete block design. Data collected were weed species composition, weed density and dry weight, nodule dry weight, pods per plant, grain weight and grain yield of soybean. Results indicated that weeds with highest relative density values across all the nutrient combinations were Ageratum conyzoides and Kyllinga sp., and other notable species included Mitracarpus villosus, Oldenlandia corymbosa, Sida rhombifolia, Paspalum scrobiculatum, Cynodon dactylon, Digitaria horizontalis Cyperus rotundus and Cyperus difformis. Years had a significant effect on weed density, weed dry weight, nodule dry weight, number of pods per plant and grain weight, number of pods per plant and grain weight of soybean. Weed density and dry weight, and weight of nodules, number of pods and grain weight of soybean were lower in 2015 compared to 2016. Among the treatments, I + P + K + M reduced weed dry weight better than I + P + K + M + CD. Average over the years, soybean grain yield was enhanced with the integration of I + P, I + P + K, I + P + K + M, I + P + K + M. However, the highest grain yield was obtained with the integration of I + P +K + M + CD which is recommended for soybean production in this agroecology of Nigeria.