Competitiveness of sesame and mung bean crops in both monocropping and intercropping systems

Intercropping is one of the effective agroecological systems which presence of two or more crops in this system will increase total yield due to improving some resource use efficiencies such as nutrient and light (Aynehband et al., 2010). In this regard, it has been found that-in corn-mung bean intercropping system the highest forage yield was belonged to 75% corn and 25% mung bean density ratio (Aynehband & Behroz, 2011). Hence, the aim of this study was to evaluate the competitive ability of sesame and mung bean crops in intercropping system and its effects on grain yield of these crops in Ahvaz. In this research, a field experiment was conducted for one year (2012) at the experimental farm of Collage of Agriculture, Shahid Chamran University, Ahvaz, Iran. Experimental design was split-plot based on RCB with three replications. Main plot was included two planting patterns with 50 and 75 cm inter-rows and sub-plots were included five plant density ratios with 100% sesame or mung bean and, 25% - 75%, 50% - 50%, 75% - 25% of each crop. Finally, grain and biological yield of both crop in monocropping and double cropping were calculated and also some competitive indices such as LER: Land equivalent ratio, AYL: Actual yield loss, A: Aggressivity, K: Relative crowding coefficient, RCI: Relative competition intensity, CR: Competitive ratio and ACI: Absolute competition intensity were computed. Our result showed that both 50 and 75 cm inter-rows in 50+50% density ratios had the highest intercrop grain yield, respectively (2.05 and 2 t.ha-1). In the most treatments, sesame had the higher grain yield than Mung bean. Increasing plant density had a positive effect on yield improving of both crops and increasing of inter-row had more positive effect on grain yield than biological yield. The harvest index (HI) was improved by increasing of inter-row due to increase in grain yield and decrease in biological yield. The LER index was higher than one in all intercropping treatments which mirror the priority of intercropping systems compared to mono-cropping systems. In both inter-rows and in 50% and 75% sesame density, LER of sesame was higher than LER of mung bean. The highest LER (1.34) belonged to 50–50% density ratio of each crop and changing in inter-row had not effect on LER. In addition, reduction in sesame density ratio (less than 25%) converts this crop to lower aggressive crop. When density ratio of mung bean was more than 75%, this crop had a suitable aggressive situation in canopy. At the same planting density (e.g. 50%+50%), sesame will be more aggressive crop and also, have higher use of inputs than mung bean. Without change in density ratio, increase in inter-rows, increased the aggressively of sesame (from 0.15 to 0.17), while this situation decreased the aggressively of mung bean (from –0.15 to –0.17). It is found that, ignoring the density ratios, wider inter-row caused increase in sesame aggressively (from 0.15 to 0.17), but, this situation had opposite effect on mung bean. It seems that some of these different reactions between both crops was due to differences in plant height (sesame was taller than mung bean) and the placement of pods in crop stand (sesame pods mostly located on the top of stand, but mung bean pods are in the middle of stand). These anatomic differences caused that just when mung bean density was more than 75%, this crop became more aggressive than sesame. It is concluded that sesame had higher competition ability than mung bean, so this crop was dominant crop in intercropping system. Sesame also had higher relative crowding coefficient. This advantage caused to this fact that sesame had a decisive role to shape the intercropping canopy arrangement, but mung bean had a lower change in actual yield loss than sesame in intercropping system. In addition, 50% - 50% density ratio was the optimum intercropping density due to the highest grain yield and also, 75 cm inter-row was the best cropping pattern due to optimum competition ability. It is also found that the grain yield is not the only appropriate parameter in intercropping system; therefore the other competition indices for this system should also be considered.