Abstract: The objective of this study was to screen green manure crops suitable for planting in dryland winter wheat fallow period of southern Shanxi Province, and thus to provide theoretical basis for green production of winter wheat. An experiment was conducted to examine the effects of planting different green manure crops (sweet clover, sun hemp, soybean, black soybean, mung bean and catjang cowpea) on the amount of nutrient returning, soil microbial biomass carbon (MBC) and nitrogen (MBN), dissolved organic carbon (DOC) and nitrogen (DON), particulate organic carbon (POC) and nitrogen (PON), light fraction organic carbon (LFOC) and nitrogen (LFON), heavy fraction carbon (HFOC) and nitrogen (HFON). Results showed that total content of returning nutrient (N+P2O5+K2O) of mung bean and catjang cowpea treatments were the highest among all green manure crops, which ranged from 104.77 kg·hm-2 to 121.82 kg·hm-2. Compared with traditional farming pattern, planting green manure crops significantly increased MBC by 27%-57%, but did not affect MBN. There was no significant difference in soil DOC, POC, HFOC, LFON and HFON contents among different treatments. Compared with traditional farming pattern, black soybean and mung bean treatments significantly increased soil DON content by 27%-55%, and the soybean treatment significantly increased soil PON and LFOC content by 31% and 162%, respectively. Our results indicated that planting soybean, mung bean, and black soybean during summer fallow period had relatively high nutrient return and consequently positive effect on soil active organic carbon and nitrogen pools of winter wheat fields in the dry Loess Plateau.

Key words: winter wheat, green manure, soil organic carbon component, soil organic nitrogen component.