Influence of winter crop residue and nitrogen form on greenhouse gas emissions from acidic paddy soil

We conducted an incubation experiment to explore the effect of different crop shoot residues (milk vetch, ryegrass, winter wheat and rape) and nitrogen forms (no fertilizer, CO(NH2)2, (NH4)2SO4 and KNO3) on greenhouse gas CO2, CH4 and N2O emissions from submerged paddy soils. Regardless of nitrogen form, cumulative CO2 and CH4 emissions were in the order of milk vetch > ryegrass > winter wheat > rape. (NH4)2SO4 and KNO3 application decreased CO2 emissions in comparison to treatments without N application. Compared with other N form fertilizer treatments, KNO3 application dramatically stimulated N2O emissions and inhibited CH4 emissions at all crop residue treatments. In the presence of KNO3, N2O emissions of milk vetch and ryegrass residue treatments were significantly higher than those of winter wheat and rape residue treatments. CO(NH2)2 application significantly lowered the N2O emissions from soils with rape residue amendment and increased that from soil with milk vetch residue amendment. We suspected that the differences among these treatments might due to differences of the speed of inorganic N immobilization and N release during crop residue decomposition. Milk vetch + (NH4)2SO4, rape + CO(NH2)2 and ryegrass + (NH4)2SO4 combinations got the relatively low global warming potential, which were recommended to reduce the global warming potentials in paddy soils.