[Effects of different amounts of straw return and nitrogen fertilizer application on soil CO₂ emission from maize...

Understanding the effects of different amounts of straw returning and nitrogen fertilizer application on soil CO₂ emission from maize field can provide theoretical support for carbon sequestration and CO₂ emission reduction and the implementation of black soil region conservation plan. Three rates of straw returning were set up in the semi-arid area of northwest Liaoning Province, China, i.e. 3000 (S₁), 6000 (S₂) and 9000 kg·hm^-2(S₃, full amount of straw returned to the field); crossed with three nitrogen fertilizer application rates in the sub-region, respectively, i.e. 105 (N₁), 210 (N₂, conventional nitrogen application rate) and 420 kg N·hm^-2(N₃). In addition, there was a control treatment (CK) without nitrogen fertilizer and straw returning. Soil samples were collected after 4 years field experiment with maize plantation. The influence of different treatments on maize field soil CO₂ emission and the relationship between CO₂ emission and soil dissolved organic carbon (DOC) and microbial biomass carbon (MBC) were investigated in an incubation experiment. The results showed that both of straw returning and nitrogen fertilizer application promoted soil CO₂ emission in maize field, which were increased significantly with the increases of straw returning amount and nitrogen application amount. Nitrogen fertilizer application was the most important factor promoting soil CO₂ emission in maize field. Straw returning combined with nitrogen fertilizer promoted soil CO₂ emission by increasing microbial biomass and increasing DOC consumption. MBC and DOC stimulated soil CO₂ emission significantly in maize field, and were mainly affected by their contents in the early stage of incubation. From the perspective of ensuring the fertilization of straw return to the field while reducing CO₂ emissions, results from our experiment showed that 210 kg N·hm^-2 conventional nitrogen application in combination with 6000 kg N·hm^-2 straw returning (N₂S₂) was the most promising mode in the semi-arid area of northwest Liaoning Province.