Effect of farmyard manure and mineral fertilizers on maize yield and soil properties in Huye and Bugesera Districts of Rwanda
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Agriculture in Rwanda is today characterized by low agricultural productivity due to soil fertility decline. This is mainly attributed to the mining of nutrients due to continuous cropping without adequate external addition of inputs. The adoption of Integrated Soil Fertility Management (ISFM) technologies such as the combination of organic manure and mineral fertilizers is being taken as one of solutions to this situation. A study was therefore, conducted to investigate the effects of farmyard manure and mineral fertilizers on maize yield response, crop nutrient uptake, nutrient use efficiency and to evaluate changes of bio-chemical soil properties brought about by the treatments applied. The study was conducted at the Research Stations of Rwanda Agriculture Board (RAB), namely, at Rubona in Huye and at Karama in Bugesera Districts in Southern and Eastern provinces of Rwanda,respectively. The experiment was arranged in a randomized complete block design (RCBD) with three factors : nitrogen, phosphorus fertilizers and farmyard manure. Nitrogen and phosphorus fertilizers were applied at three levels, 0, 50 and 100 Kg/ha for nitrogen and 0, 25 and 50 kg/ha for phosphorus while Manure levels were two (0 and 10 tons/ha). Maize was the test crop and was planted in plots measuring 4.5 x 4.5 m with a spacing of 75 x 30 cm. The experiments were replicated three times. Soils samples were analyzed for soil pH, soil organic Carbon, total N, available phosphorus,Potassium, CEC, ECEC, Exchangeable acidity and microbial status of the soil. Maize grains were dried after harvest and weighed at 12.5% moisture content. The data was analyzed by ANOVA using general linear model of SAS software. Regression and correlation were used to establish relationships between measured parameters. The results showed that maize grain yield,1000 grain weight and stover biomass were influenced significantly (P<0.05) by the application of farmyard manure and inorganic fertilizers. The combined applications produced yields which were significantly higher than organic or inorganic alone and the control. The highest grain yields of 8.92 tons ha-1 and 7.11 tons ha-1 were obtained in the combined treatments of farmyard manure with mineral fertilizer at a rate of 100 kg ha-1 N, 50kg ha-1 P mineral fertilizer and 10 tons ha-1 manure at both sites (Rubona and Karama), while the controls recorded the lowest grain yields of 4.61 tons ha-1 and 3.23 tons ha-1 for Rubona and Karama sites,respectively. The combined treatments generally showed significantly higher nutrient uptake and nutrient use efficiency than the sole organic and inorganic fertilizers. In the evaluation of soil properties, total nitrogen, K and pH significantly decreased in plots treated with organic and inorganic fertilizers while soil organic C, available P, Ca, Mg and CEC increased generally in treatments under inorganic plus organic fertilizers. In the case of microbial biomass, there were slight increase for both bacteria and fungi after NP fertilizers and manure combined treatments. In both sites, maize yields responded more to nitrogen fertilizer than P fertilizer, an indication of low nitrogen content in the soils of Rubona and Karama.