Soil organic carbon contents as a result of various organic amendments to a vertisol

The present study estimates the contributions of various organic amendments to soil organic carbon (SOC). The present work discusses data from a 32-year fertilization experiment using vertisol soil. Five treatments with four field replications were included: no fertilizer (CK), mineral fertilizers only (NPK), wheat straw plus NPK (SNPK), swine manure plus NPK (PMNPK), and cattle manure plus NPK (CMNPK). The 13C signature of SOC was measured by δ 13C natural isotope technology, and the carbon functional compositions of organic amendments were determined by solid-state 13C nuclear magnetic resonance spectra. The average proportions of native and crop residues derived organic carbon under the SNPK, PMNPK and CMNPK treatments were 43, 40, 29, and 51, 51, 39%, respectively. The average proportions of organic carbon-derived from wheat straw (SNPK), swine and cattle manure (PMNPK and CMNPK) were 6, 9, and 32%, respectively. The quantitative relationship between carbon retention efficiency and fertilization year could be described by a significantly negative linear function (p < 0.05). The average organic carbon retention efficiencies for wheat straw, swine, and cattle manure differed substantially at 6, 10, and 31%, respectively. Their corresponding aromatic carbon contents were 6, 7, and 12%, respectively. Furthermore, incorporation of organic amendments, especially for cattle manure, led to a decrease in the yield variability and an increase in the sustainable yield index of crops compared with the CK and NPK treatments. In conclusion, the long-term continuous application of cattle manure is a preferred method for enhancing SOC storage and increasing crop production for vertisols.