Effect of seeding ratio and time of planting of cowpea (Vigna unguiculata) intercropping with maize (Zea mays) on agronomic parameters, forage biomass and grain yield of maize

The study was conducted at Adami Tulu and Dugda districts of Oromia regional state, Ethiopia to determine the optimum level of seeding ratio and planting time of cowpea under maize for optimum forage biomass production and maize grain yield. Combinations of four levels of cowpea seeding ratios and four different cowpea planting dates were laid out in a randomized complete block design in factorial arrangement with three replications. The levels of seeding ratios were 100%, 75%, 50%, 25%, 0% (sole maize) for the two districts. The four planting dates for cowpea were simultaneously planting with maize, 10 days after maize planting (DAMP), 20 DAMP and 30 DAMP. The results indicated that increasing seeding ratio of cowpea from 25% to the highest level (100%) resulted in significantly increased cowpea forage biomass yield. Time of cowpea planting in maize also influenced the plant height and biomass yield of cowpea. The highest forage biomass yield was recorded from simultaneously planting of the two crops. On the other hand, seeding ratio of cowpea has significantly influenced the grain yield of maize. It was also indicated that the time of cowpea planting in maize have significantly affected the grain yield of maize with simultaneously planting resulting in the lowest grain yield. The total LER in most of the intercropping system was more than one showing that intercropping of forage legumes with maize is more advantageous than sole cropping of maize. The optimum forage legume biomass yield (1.78 t/ha) was obtained from the combination of seeding ratio of 75% with 10 DAMP without significantly (p>0.05) reducing the grain yield of maize. Hence this combination was recommended for production of cowpea forage and maize grain from intercropping of the two crops in the study areas. From these results, it can be concluded that additional forage can be produced by intercropping cowpea with maize at their appropriate seeding ratio and planting time with a little or no sacrifice in maize grain yield. Moreover, it is important to further demonstrate and promote the recommended maize-cowpea intercropping practices for the end users of the study areas and similar agro-ecologies.