With the renewed interest in mixed cropping and the increasing awareness of environmental degradation arising from high chemical inputs, this experiment was conducted to assess the effect of supplementing inorganic fertilizer with an organic fertilizer on the growth and yield of component crops in a mixed crop system in 2010. Rice (Oryza sativa) cv. Leung Tawng and cowpea (Vigna unguiculata (L) Walp) cv. Tsurunashi sasage were used. Treatments comprised three sole crops of rice and cowpea, and three mixed crops, each under 100% NPK (C), 50%NPK+ 50% cow dung (CCD) and 12t/ha cow dung only (CD). Plant spacing was 0.3m X 0.6m under both cropping systems, resulting in a 1:1 ratio of rice and cowpea in the mixed crop.

Pod number and yield per square meter of cowpea were not affected by the fertilizer treatments imposed but were reduced under the mixed cropping system. Rice growth was not affected by the association with cowpea in the mixed-crop, but the fertilizer treatment imposed affected the growth. Panicles per hill and spikelet per panicle were higher in the mixed-crop rice than their sole counterparts. On average grain yield of rice was significantly less in the mixed crop compared to their sole counterparts. The performance of CD was significantly at par with CCD. The LER ranged from 1.26 – 1.47 signifying that biological efficiency was increased by mixed cropping rice with cowpea under the various nutrient treatments. Results of the experiment suggest that a rice-cowpea mixed cropping under CCD and CD is a viable production option.