effect of green manure grass pea (lathyrus sativus l.) and common vetch (vicia sativa l.) on some characteristics of soil and yields of potato and wheat in crop rotation

in order to investigate the possibility of planting grass pea and common vetch crops after harvesting wheat and to evaluate the effects of  green manure of these crops on yield of potato-wheat in croprotation cycle, this research was carried out using a randomized complete block design with four replications during 2006-2010 at khair-abad research station, zanjan, iran. the treatments were either removal or addition of grass pea and common vetch green manure as well as of wheat green manure (originating from threshing grains as the control) into the soil. analysis of the data obtained from two cycles of crop rotation revealed significant difference (at 1% level) among the treatments in terms of forage dry matter yield and nitrogen accumulation in tissues of the above ground organs. the lowest amount of dry matter (1.63-1.95 t/ha) and nitrogen accumulation (17.67-21.22 kg/ha) was recorded in the control. between grass pea and common vetch, there was no significant difference in terms of forage dry matter yield. in combined analysis of the results, the effect of treatments on mean yield of potato and biological and grain yield of wheat was significant. the highest amounts of this characteristic were obtained from addition of grass pea and common vetch green manure. in the treatment consisting of addition of common vetch green manure, the mean yields of potato (38.47 t/ha) and wheat (3.71 t/ha), mean weight diameter of soil particles (1.46), and soil organic carbon (0.77 percent) were higher than the other treatments. results of this research show the successful effects of planting grass pea and common vetch in summer fallow condition along with positive effect of green manure addition of these crops on the performance of potato and wheat and some soil characteristics.