Increasing soil organic carbon in aggregates and microflora diversity in moderate salt-affected soils through no till combined with plastic film mulching

Abstract: In a 5-year field experiment, four treatments including the conventional tillage with no mulching (CT), conventional tillage with plastic film mulching (CTP), no-tillage with no mulching (NT), and no-tillage with plastic film mulching (NTP) were carried out to study the effects of different tillage methods on the moderate saline soil, such as the soil water and salt distribution, soil structure, aggregate organic carbon, and microflora. The results showed that in the fifth year of the experiment, the average water content of no-tillage treatments (NT and NTP) increased by 5.60% (before spring irrigation), 5.10% (after spring irrigation) than that of the tillage treatments (CT and CTP) in the 40-60 cm soil layer. Before spring irrigation, the average salt content of no-tillage treatments in the soil layers of 0-40 cm decreased by 36.53% (NT) and 11.66% (NTP), compared to that of the tillage treatments of CT and CTP. But after irrigation, the average salt of no-tillage treatments was lower than that of CT by 25.27%, whereas higher than that of CTP by 13.15%. After harvest, the accumulation rates in the soil layers of 0-20 cm under the CT, CTP, NT and NTP treatments were 99.16%, 26.33%, 21.18% and -6.26%, while the accumulation rates in 0-20 cm layers were 48.89%, 55.14%, 4.71% and 3.64%, respectively. These values indicated that the desalination occurred in the soil layer of 40-60 cm, in which the salt accumulation was observed in the no-tillage treatments, because both tillage treatments caused more salt to move up to the tillage layer. After harvest, the average content of macro aggregate (>0.25 mm) in the layers of 0-40cm under the NT and NTP was significantly higher by 53.41% than that of the tillage treatments, whereas the content of macro aggregates (>1 mm) under the NTP was higher by 40% than that of NT. Moreover, soil organic carbon in 0-40 cm layers?under NT, NTP treatments significantly increased by 16.44%, 15.48% than that of CT, CTP, respectively. There were also a great increase in the amount of soil bacteria, antinomies and fungus in the NTP after harvest. The correlation analysis demonstrated that the amount of the bacteria was negatively correlated with the salt content of soil, but positively correlated with the macro aggregate (>0.25 mm) and the soil organic carbon. The amount of antinomies was negatively correlated with the salt content of soil. The data from the high-throughput sequencing technology also showed that the Shannon index under the NTP treatment was higher than that under the CT and CTP treatments. Meanwhile, the factor analysis showed that the community changes 50.9% in the soil organic carbon and 29.4% in macro aggregate (>0.25 mm), indicating both were main environmental factors on the soil bacterial community structure. The no-tillage with plastic film mulching can contribute to the salt accumulation, the improvement of soil structure, the increase SOC sequestration, and microbial diversity, and therefore can serve as a promising approach to increase the soil fertility in Hetao Irrigation regions of China.