evaluation of yield and yield components in additive intercropping of grain sorghum )sorghum bicolor l.( and cowpea )vigna unguiculata l.) under complete and limited irrigation conditions

to evaluate the yield and yield components in additive intercropping system of grain sorghum (sorghum bicolor l.) and cowpea (vigna unguiculata l.) under limited irrigation condition, an experiment was conducted in research farm of college of agriculture, university of tehran, during spring 2006. the experimental treatments were arranged in split plots based on a complete randomized block design with four replications. the limited irrigation (moisture stress) treatments of ir1: normal weekly irrigation (control), ir2: moderate moisture stress during vegetative and generative growth, ir3: moderate moisture stress during vegetative and severe during generative growth, ir4:severe moisture stress during vegetative and moderate during generative growth, were allocated to the main plots and different combinations of sorghum and cowpea in additive intercropping systems of s1: sole sorghum (weed free), s2, s3 and s4 additive series of 15, 30 and 45% of the sole cowpea seed rate mixed with full sorghum seed rate, respectively and s5: sole sorghum (weeded), were allocated to sub plots. the results of the experiment showed that there was a significant effect of limited irrigation systems, additive intercropping systems and their interaction on yield and yield components of sorghum and cowpea. the highest grain yield of sorghum was obtained in normal weekly irrigation treatment (control) which was followed by ir2 irrigation system. the same result was obtained in weed free sorghum treatment which was followed by additive mixture of sorghum+45% cowpea. additive mixture of sorghum+45% cowpea was the most stable production system at different limited irrigation systems. the highest total sorghum yield (equivalent yield) was obtained in ir1-s4 treatment which was followed by ir2-s4. based on the results of this experiment the additive mixed cropping of sorghum+ 45% sole seed rate cowpea at moderate limited irrigation (ir2) could be recommended for yield advantages, higher income, and more efficient utilization of resources in arid and semi arid areas of iran.