The role of intercropping maize ( Zea mays L.) and Cowpea ( Vigna unguiculata L.) on yield and soil chemical properties

Farmers in Sistan region experience low crop yields of crops due to low soil fertility. Sole crops and intercrops of maize (Zea mays L.) and cowpea (Vigna unguiculata L.) were studied at eight planting ratios of maize: cowpea (100:100, 50:100, 100:50, 25:75, 75:25, 50:50, 0:100 and 100:0) and two harvest times (milky stage and doughy stage). This experiment was carried during two years (2007 and 2008) on Research Center, University of Zabol, Iran, to investigate the influence of cowpea on the soil fertility and sole maize (SM) as control. Measurements of nitrogen, phosphorous, potassium soil and crop yield were carried out to study the effects of intercropping on crop yield in a cowpea-maize intercropping system in Sistan at southeast of Iran. We found that intercropping increased the amount nitrogen (N), phosphorous (P) and potassium (K) contents compared to sole crop of maize. The highest amount of N, P, K in soil was obtained at sole cowpea and 100% cowpea + 100% maize with no significant difference to 100% cowpea + 50% maize. The lowest amount of N, P, and K was obtained at sole maize and 75% maize + 25% cowpea. Intercropping system had significant effects on soil fertility and crop yield. LER (land equivalent ratio) values were greater in all intercropping systems with different planting ratios which indicated yield advantage of intercropping over sole cropping of maize. Results indicate that intercropping can increase nutrient elements of soil compared to sole maize and improve conservation of soil fertility. Based on high grain and improve soil fertility intercrop productivity compared to sole crop could be selected for improving the productivity of maize/cowpea mixture in the Southeast of Iran.   Key words: Intercropping system, maize - cowpea, soil fertility, land equivalent ratio.