Effects of Different Straw Returning Patterns on Soil CO₂ Emission and Carbon Balance in Maize Field

The effects of different straw returning patterns on soil carbon dioxide (CO₂) emission characteristics and carbon balance were discussed, which provided a scientific basis for carbon (C) sequestration and emission reduction as well as the selection of straw returning patterns in Northeast China.

A field micro-plot experiment were conducted with maize as the experimental crop, and three straw returning patterns were set up, including straw shallow returning (QH), straw deep returning (SH), and straw mulching (FG). No straw returning (CK) was used as the control treatment. The LI-8100A automatic soil C flux tester was used to monitor soil CO₂ emission characteristics under different straw returning patterns during the maize growth period. Effects of soil temperature, soil moisture content, pH, MBC, available nutrients and total nutrients of nitrogen, phosphorus and potassium on soil CO₂ emissions were analyzed, and soil carbon balance was investigated too.

During the maize season, soil CO₂ emission rates showed a trend of first increasing and then decreasing under different straw returning patterns. The cumulative soil CO₂ emissions were as follows: FG>QH>SH>CK treatment. Compared with SH treatment, the cumulative soil CO₂ emissions under FG and QH treatments increased by 14.0% and 6.4%, respectively. There was a significant difference between the treatments (P<0.05). The single factor model fitting of soil CO₂ emission rates, soil temperature and soil moisture content under different straw returning patterns showed a quadratic function correlation, and reached a significant level (P<0.05), soil temperature could explain the variation of soil CO₂ emission rate of 68.2%-73.7%, and soil moisture content could explain 21.3%-37.5%. However, the two-factor composite model of soil temperature and soil moisture content could better explain the variation of soil CO₂ emission rate, with an explanation of 78.5%-82.8%. Correlation analysis showed that cumulative CO₂ emissions were significantly correlated with available potassium and MBC (P<0.01), and significantly correlated with soil organic matter, available nitrogen, total nitrogen, and pH (P<0.05). The soil carbon balance was positive under different straw returning patterns, which were the "sink" of atmospheric carbon dioxide. The soil carbon balance and carbon sequestration potential under the SH treatment were significantly higher than the QH and FG treatments by increased of 23.4%, 475.7% and 7.1%, 30.7% (P<0.05), respectively. Compared with other treatments, the SH treatment showed a strong carbon "sink" function. In the two-year harvest period, straw returning treatments significantly increased maize yield, SH treatment had the highest maize yield, but there was no significant difference with QH and FG treatments.

Therefore, under the conditions of this experiment, taking into account the carbon sequestration and emission reduction effect and yield, SH was a better straw returning pattern compared with the three patterns.