Assessment of the Inter-and Intra- Specific Competition of Sorghum-Bean Intercropping Using Reciprocal Yield Approach

Assessment of competition ability in intercropping is very important in mixed cropping experiments. A field study was conducted to examine the effects of density and sowing rate on individual plant yield and competition between grain sorghum (promising line M5) and bean (cv. Talash) using reciprocal yield approach in Khorasan-e-Razavi Agricultural and Natural Resource Research Center, Mashhad, Iran, in 2007 cropping season. Three densities (low 19.2 and 6.3, medium 38.4 and 12.8, high 59.17 and 25.6 bean and sorghum plant (per m-2), respectively and five sowing rate (0 : 100, 100 : 0, 67 : 33, 50 : 50, 33 : 67 sorghum to bean) constituted the experimental factors. The experiment was factorial arrangement in randomized complete block design with three replications .The relationship of density and yield per plant and competitive models were fitted by Spitters approach. Results showed that intra-specific competition for sorghum grain yield was greater than inter-specific competition, and in bean this was reverse. Relative competition ability revealed that the effect of one plant of sorghum on its reciprocal grain and biological yields was equal to the effect of 4.93 and 46.97 plants of bean on the reciprocal grain and biological yields of sorghum individual plant. Reciprocal grain and biological yields for bean showed that each 0.44 and 1.03 plant of sorghum had an effect of equal to one plant of bean reciprocal grain and biological yield of individual bean plant. Niche differentiation index and land equivalent ratio was greater than one, therefore, sorghum and bean are two compatible species for intercropping systems.