As the main national grain production region, Northeast China has 14.7 million hectares cultivated Mollisol (black soil) which is generally considered as inherently fertile, corresponding to around 20% of total grain production. However, the content of soil organic matter (SOM) of Mollisols has been experiencing a rapid decrease in Northeast China over the past decades as a result of long-term unsustainable agricultural practices.
The conventional management practice in northeast China is to remove aboveground crop residue completely after harvest. In recent years, returning crop residues to soil is encouraged and widely adopted aiming to improving soil fertility and mitigating SOM loss. However, the dynamics and chemical composition of SOM under long-term straw return in Mollisols are not fully understood yet.
Recently, researchers from the Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences (CAS) revealed the effects of 15 years of continuous straw return on SOC dynamic and composition in a soybean-maize rotation cropping system. The study was based on a 15-year long-term field experiment in Hailun National Observation and Research Station of Agroecosystems, CAS.
The long-term field experiment including three treatments, no fertilization (NF), mineral fertilizers (NPK) and mineral fertilizers with straw return (NPKS). Researchers found that after 15-year continuous straw return, SOM content increased by 14.2%. Meanwhile, crop straw return significantly increased the contents of labile fractions of SOM, including microbial biomass carbon (C), water-soluble organic C, light fraction C, readily oxidizable organic C, and particulate organic C.
The δ13C values of SOC increased with time under all treatments, and its positive relationship with cumulative maize C input indicated a larger C contribution to SOC from maize than soybean residues. The Fourier transform infrared spectroscopy analysis revealed that SOM in NPKS becomes enriched by aliphatic components and reduced by aromatic components, suggesting that the humification degree of SOM became lower with straw return.
The study demonstrate that straw return could continuously increase SOC in an inter-annual rotation of soybean and maize cropping system in Mollisol. Furthermore, long-term fertilization can alter SOM chemical composition.
The study has been published in Soil & Tillage Research entitled “Dynamics and composition of soil organic carbon in response to 15 years of straw return in a Mollisol”, and it was financially supported by the National Natural Science Foundation of China, the Research Program of Frontier Sciences and the Strategic Priority Research Program of the Chinese Academy of Sciences.