Abstract: [Objective] To assess the effects of overturning of three green manure crops, Lolium multiflorum, barley and oilseed rape, on soil quality under irrigation with varied concentrations of biogas slurry. [Method] Under two biogas slurry concentrations, 8.5 L/m² （L1） and 17 L/m² （L2）, the green manures of Lolium multiflorum, barley and oilseed rape were applied, respectively. Under L1 biogas slurry concentration, experimental groups of Lolium multiflorum （L1）, barley （L1）, oilseed rape （L1） were set, and a control group of CL1 with biogas slurry irrigation without application of green manures were included. Under L2 biogas slurry concentration, experimental groups of Lolium multiflorum （L2）, barley （L2）, oilseed rape （L2） were set, and a control group of CL2 with biogas slurry irrigation without application of green manures were included. The differences in pH value as well as contents of organic matter and total nitrogen in soil were statistically analyzed among groups with the same biogas slurry concentration and the different varieties of green manures. [Result] After 110 days of green manures application, the soil pH value of Lolium multiflorum （L2） and barley （L2） groups was significantly （P<0.05） higher than that of CL2 group, with a mere 0.17 rise. The soil salinity of barley (L1) and Lolium multiflorum （L2） groups was significantly （P<0.05） higher than that of CL1 and CL2 groups, respectively. The content of soil organic matter of the two barley groups was significantly （P<0.05） higher than that of their respective control groups. The content of soil organic matter of oilseed rape （L2） group was also significantly （P<0.05） higher than that of CL2 group. The soil total nitrogen content of the two barley groups was significantly （P<0.05） higher than that of their respective control groups. The soil available phosphorus content of Lolium multiflorum （L1） and barley （L1） groups was significantly （P<0.05） higher than that of CL1 group. The soil available potassium content of barley （L2） group was significantly （P<0.05） higher than that of CL2 group. [Conclusion] The application of three varieties of green manures has different effects on soil improvement after biogas slurry irrigation. Barley significantly increases the soil contents of organic matter and total nitrogen when nitrogen fertilizer is replaced by both concentrations of biogas slurry. In addition, barley greatly increases the content of soil available phosphorus under low biogas slurry concentration, and significantly increases the content of soil available potassium under high biogas slurry concentration, suggesting that it can be utilized as a new type of green manure.

Key words: Lolium multiflorum, barley, oilseed rape, green manure, biogas slurry, soil nutrients