Long-term straw mulch effects on crop yields and soil organic carbon fractions at different depths under a no-till system on the Chengdu Plain, China

Proposal A 12-year field experiment was conducted to assess straw mulch effects on soil organic carbon fractions, the carbon pool management index (CPMI) at different depths, and crop yield under a no-till rice-wheat rotation system on the Chengdu Plain, southwestern China. Materials and methods There were two treatments in the experiment: no-till without straw mulch (CK) and no-till with straw mulch (SM). The soil was sampled at 0-5, 5-10, 10-20, and 20-30-cm depths. Soil total organic carbon (TOC), the labile organic carbon fractions, including particulate organic carbon (POC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and permanganate-oxidizable carbon (KMnO4-C), and the CPMI were analyzed. The crop grains were measured between September 2013 and May 2018. Results and discussion Between 2013 and 2018, rice and wheat grain yields under SM were comparable to CK, except there were higher rice yields in 2016 and higher wheat yields in 2017 under SM. The soil organic carbon decreased as soil depth increased in both treatments. Soil TOC, POC, and KMnO4-C concentrations at 0-5 and 5-10 cm, CPMI at 0-5 and 5-10 cm, and DOC at 0-5, 5-10, and 10-20-cm soil depths were significantly greater under SM than under CK, whereas the MBC at 0-5 and 5-10 cm under SM was lower than CK. The POC/TOC, KMnO4-C/TOC, and DOC/TOC ratios were greater under SM in the 0-5 and 5-10cm, 0-5 cm, and 5-10 and 10-20-cm layers than CK, respectively, whereas the MBC/TOC ratio decreased under SM at 0-5, 5-10, and 10-20-cm depths. Conclusions The results showed that straw mulching should be adopted when a no-till rice-wheat cropping system is used in southwestern China because it leads to effective improvements in SOC sequestration while still maintaining normal crop yields.