ObjectivesEffects of fertilization and straw mulch on the contents of soil labile organic matter and carbon management index were investigated to evaluate the sustainable straw mulch methods for Weibei rain-fed Highland of China.

MethodsA 28-year-long field experiment, located in Heyang County, Shaanxi Province since 1981, was used for the study. Five treatments were included in this experiment, neither fertilization nor straw mulch (CK), nitrogen and phosphate co-application (NP), nitrogen, phosphate and manure co-application (NPM), nitrogen and phosphate and straw mulch together (NP + FG), and nitrogen, phosphate and manure co-application and straw mulch (NPM + FG). The contents of total organic matter, labile organic matter and soil nutrients and soil enzyme activities were measured. The contents of soil labile organic matter and carbon management index were studied. Further, their correlations with soil enzyme activities, soil nutrient contents were revealed. The contents of soil labile organic matter were measured using the KMnO₄oxidation method.

Results1) Compared with CK, the NP increased the content of high labile organic matter by 48.7%, and had no significant influence on other fractions of labile organic matter. The NPM increased the content of total organic matter by 120.0%, and increased the high-labile, middle-labile and low-labile organic matter by 137.4%, 136.3% and 93.4%, respectively. 2) Taken the CK as reference soil, the high labile carbon management index (HCMI), mid-labile carbon management index (MCMI) and carbon management index (CMI) in the treatment NP were increased by 54.66, 17.93 and 2.65, in the treatment NPM were increased by 139.28, 140.92 and 83.59; taken NP as reference soil, those in the treatment NP+FG were by 75.01, 191.43 and 122.90, and compared to NPM, those in the NPM+FG were by 58.93, 121.35 and 93.43. 3) All the three fractions of labile organic matter were very significantly correlated with total organic matter, HLOM and HCMI were very significantly correlated with the invertase activity, MCMI and CMI were significantly correlated with the invertase activity. Compared with total organic matter, labile organic matter could reflect the change of soil enzyme activities and soil quality more sensitively.

ConclusionHCMI was affected by the NP application obviously, and HCMI, MCMI and CMI were affected by the NPM obviously. The effects of straw mulch on CMI were evident, being more evident under the condition of NP fertilization than under the condition of NPM fertilization. Straw mulch under the condition of NP fertilization could increase soil carbon management index and improve soil fertility better in Weibei rain-fed tableland of China.