Field experiments were conducted at Welenchity experimental field site, Melkassa Agricultural Research Center from June to October during the years 2010 and 2011 cropping seasons. The aim of the study was to determine optimum time of intercropping haricot bean into the maize based cropping system under conservation tillage practices, Tied-ridge and Zero-tillage. The experiment was laid out in split-plot design, with tillage practices a) Tied-ridge and b) Zero-tillage as main plot and time of intercropping haricot bean 1) Planting haricot bean simultaneously with maize, 2) Planting haricot bean 15 days after maize was planted and 3) planting haricot bean 30 days after maize was planted as sub-plots. Intercropping was assessed on the basis of the performance of the main and component crops indices as grain yield, biomass weight, partial and total LER and competitive indices such as relative crowding coefficient (K), aggressivity (A), competitive ratio (CR) and system productivity index (SPI).There was no interaction between tillage practices and time of intercropping haricot bean in any of the indices studied. Main effects of tillage practices had no significant effects on all the indices considered during both 2010 and 2011 growing seasons, but grain yield, biomass weight, partial and total LER tended to be higher in the tied-ridge treatment during 2010 and vis-versa during 2011seasons. The results obtained showed that the greatest intercrop yields of maize and haricot bean were obtained when both crops were planted at the same time. In both years, highest total land equivalent ratio (LERt) values were obtained when planting of maize and haricot bean was done at the same time followed by planting of haricot bean 15 days after maize was planted indicating the advantages of intercropping over the sole planting. Partial LERm was always higher than LERb during 2010 season and vis-versa during 2011 season. The results of competitive indices indicate that maize was the dominant crop in the mixture as measured
by the positive values of A, and the high values of Km than Kb in the mixture. On the other hand, CR values of haricot bean were higher than maize in the mixture suggesting haricot bean was more competitive than maize in the intercropping system. Moreover, the data of SPI indicated that intercropping haricot bean at the same time with maize had higher SPI during both 2010 and 2011 season. In conclusion, intercropping of haricot bean simultaneously with maize exhibited an overall advantage over the other time of intercropping and sole cropping in terms of grain yield, partial LERm, LERb and LERt and competitive ratio indices and could therefore be recommended for Central rift valley areas of Ethiopia where maize and haricot bean are major crops.
