Effects of rice straw incorporation and N fertilizer on ryegrass yield, soil quality, and greenhouse gas emissions from paddy soil

Abstract

Ryegrass is usually rotated with rice in southern China. The influences of returning ryegrass residues on rice yield and soil dynamics have been studied extensively, but little is known about the effects of returning rice straw on ryegrass growth and soil variations. We investigated the effect of straw incorporation and the N fertilizer rate on the ryegrass yield, soil quality, and CO2 and N2O dynamics from soils planted with ryegrass. Irrespective of the incorporation rate, N fertilizer promoted ryegrass yield. In comparison to moderate incorporation treatments, high incorporation lowered the ryegrass yield in the low N fertilizer treatments, whereas high straw input increased the yield in the high N treatments. When low N fertilizer was applied, the soil phosphatase, β-glucosidase, and sucrase of straw incorporation treatments were significantly higher than those of non-straw incorporation treatments. Nevertheless, catalase, phosphatase, and β-glucosidase showed no significant differences among straw incorporation treatments in the high N fertilizer groups. In the low N fertilizer treatments, the high incorporation rate increased cumulative CO2 and N2O emissions. However, with low N application, compared with non-straw incorporation treatments, the moderate incorporation had no effect on the cumulative CO2 emissions/ryegrass yield but significantly reduced the cumulative N2O emissions/ryegrass yield. These results suggested that moderate straw incorporation in combination with low N fertilizer could enhance soil activity and benefit both the mitigation of greenhouse gas emissions and forage yield.