Effects of Double Cropping Grass Pea and Common Vetch as Green Manure on some Properties of Soil and Yield of Onion and Wheat in Crop Rotation Cycle

This research was carried out using a layout of randomized complete block design with four replications during 2004-2008 at Khair-Abad Research Station, Zanjan, Iran. The treatments were either removal or adding of grass pea and common vetch green manure and adding wheat green manure (originated from threshing grains as control) into the soil. In results obtained from two cycles of crop rotation, although there was no significant difference between grass pea and common vetch in terms of mean dry matter yield but total dry matter yield obtained from two rotation cycle in grass pea was 24.2% more than of common vetch. In each of two rotation cycles, there was significant difference (p≥ 0.01) among the treatments regarding dry matter of green manure and nitrogen accumulation in tissues of the above ground organs. In each of two cycle rotation, the least amount of dry matter (0.29-0.63 tha-1) and nitrogen accumulation (3.98-9.12 kgha-1) was obtained from control treatment. The treatments effect on onion yield, weight of soil particles diameter, soil organic carbon percent, biological and grain wheat yield were not significant. Highest values of these characters were obtained from adding green manure grass pea and common vetch treatments. Mean wheat biological yield (18.5 tha-1), wheat grain yield (7.23 tha-1), mean weight of soil particles diameter (1.69) and soil organic carbon percent (0.915) in grass pea green manure added treatment, was 12.8, 14.6, 13.4 and 0.2 percent higher than check treatment, respectively.