Effect Of Mulching On Soil Organic Carbon And Its Fractions In Rainfed Farmland

Soil surface mulching with straw or plastic film has been widely adopted in the rainfed farmlands due to its effects on soil water conservation and crop yield-increasing. Soil physical environment could be altered greatly by surface mulching, which would affect soil carbon cycling. In this study, based on a5-year field experiment, we explored the responses of soil organic carbon (SOC) and its fractions changes to different mulching measures with straw and plastic film in winter wheat and spring corn fields, and aim to elucidate the long term changes in soil organic carbon pool as affected by soil surface mulching.Five treatments were included in the winter wheat field as control without mulching (CK), wheat straw mulching at a rate of9000kg/hm2(M9000) and4500kg/hm2(M4500) and plastic film mulching (PM) during growing season, and wheat straw mulching during summer fallow (SF). The results showed that compared with CK without mulching, straw mulching increased soil organic carbon (TOC), carbon mineralization potential (PCM), microbial biomass carbon (MBC), particulate organic carbon (POC) and soil carbon management index, especially for M9000, and plastic film mulching has less effect on soil organic carbon and its index. Averaged from2009to2013, compared with that in CK, the contents of SOC, PCM, MBC and POC at0-10cm soil layer were significantly higher by.6.1%,23.1%,49.8%and58.7%in M9000, respectively. Similarly, soil PCM, MBC and POC were higher by10.3%,33.3%and34.3%in M4500than in CK, respectively. Treatment SF and PM increased MBC by29.6%and25.1%than CK, respectively. At10～20cm soil layers, the contents of PCM, MBC and POC were higher by22.3%,54.8%and40.3%in M9000, PCM and POC were higher by10.3%and20.7%in M4500, and MBC and POC were higher by28.1%and17.4%in SF when compared with that in CK, respectively. At0-20cm soil layers, compared with CK, treatment M9000significantly increased SOC, MBC and POC by4.9%,22.7%,45.7%and50.5%, treatment M4500significantly increased PCM, MBC and POC by11.6%,25.5%and27.9%, and treatment SF significantly increased MBC and POC by22.5%and16.5%, respectively. The proportion of fractions to SOC showed the same trend with their contents. The carbon management index after surface mulching was significantly higher than that in CK at both0～10cm and0-20cm soil layers. The content of SOC varied among five years. A negative correlation with precipitation was found for SOC and POC.In the spring corn field, three treatments were included as control without mulching (CK), corn straw mulching (SM) and plastic film mulching (PM) during growing season. The results showed that, compared with CK, SM increased both SOC and its fractions slightly, while PM significantly decreased PCM and MBC averaged across soil layers, respectively. At0～10cm soil layers, SOC, PCM and MBC were higher by4.4%,27%and48.6%in SM than in PM, respectively. Compared with CK, treatment SM significantly increased soil carbon management index at0～40cm soil layers, while PM significantly decreased soil carbon management index at20～40cm soil layers. High correlation was found among soil active organic carbons. However, only MBC was significantly associated with SOC.In general, SOC and its fractions were more affected by surface mulching in wheat field than in spring corn field. High amount of straw mulching in winter wheat field can effectively increase soil organic carbon pool and active organic carbon fractions.