International Journal of Plant & Soil Science

An experiment was carried out in Busia County, Kenya at Emalomba (N 00°25′28.8″ E 034°15′ 51.9″), Nambale District to assess the effects of nitrogen fertilizer rates and legume management options on nitrate nitrogen (NO₃-N) under intercropping system. Six soybean residue management options were considered: Sole sorghum, sorghum + soybean left to maturity, sorghum + soybean mulched, sorghum + soybean incorporated, sorghum + soybean exsitu and sorghum + soybean exsitu and plot tilled. Three levels of nitrogen (0kg N ha-¹, 40kg N ha-¹, and 80kg N ha-¹ as urea were applied as top-dress and treatments arranged in randomized complete block design. Soil NO₃-N was significantly high (P<0.0010) in topsoil with a notable leaching to subsoil due to precipitation. Control treatments had low soil NO₃-N in comparison to other treatments implying that, use of inorganic fertilizers to supplement soil N is important. Fertilizer application at 40kg N ha-¹ with respect to on-farm soybean residue management was in relation to NO₃-N supply was in the order: sorghum + soybean left to maturity > sorghum + soybean mulched = sorghum + soybean incorporated. Experimental plots with legume residues removed had significantly (P<0.001) low NO₃-N. High leaf NO₃-N observed points to transfer of N to sorghum by nitrogen fixation signifying importance of intercropping. There was no significant difference between nitrogen fertilizers applied at 40kg N ha-¹ and 80kg N ha-¹ irrespective of field managed legume residues. Sorghum intercropped with soybean left to maturity with nitrogen fertilizer applied at 40 kg N ha-¹ reflected high (P< 0.001) soil NO₃-N in comparison to the other management options. It is therefore recommended as a possible optimum rate and legume residue management option to improve soil NO3-N among small scale households with stretched socio-economic ability in Busia County.