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Purpose: Exploring how organic amendments influence carbon sequestration by affecting particulate organic carbon (POC) and determining the optimum amendment for protecting and restoring mollisol and increasing yields. Methods: Differences of POC properties and maize yields in 3-year soils amended with organic material of different origins were studied. POC was separated by a wet sieving method, and the structure was analyzed by 13C NMR spectroscopy. Results: We found that SOC accumulation in soils amended with plant origin organic materials resulted from increasing organic fractions other than POC, while that in soils amended with animal origin materials resulted from increasing POC. The proportion of POC net variation in SOC net variation was significantly negatively correlated with SOC (p < 0.01). POC, mainly composed of alkyl C and alkoxyl C (more than 68%), had its stability more accurately evaluated through combined analysis of the carbonyl C content and alkyl C/alkoxyl C ratio. The addition of organic materials improved POC stability by increasing the alkyl C/alkoxyl C ratio and decreasing the carbonyl C content. Maize yields were positively correlated with SOC content and POC stability (p < 0.01), which increased by at least 2012 kg ha−1 with the addition of organic materials. Conclusion: Increasing more stable POC will promote the carbon sink. The order of the stability of POC in mollisol amended with organic materials of different origins was woody plant material > herb material > livestock dung > poultry dung. The woody plant material was the optimum organic amendment for mollisol, enhanced POC stability, and promoted SOC sequestration while increasing the yield. [ABSTRACT FROM AUTHOR]

We conducted a 2-year field experiment which was comprised of five treatments, namely no straw returning (CK), straw mulching (SM), straw plowed into the soil (SP), and straw returned in granulated form (SG). The aim of this study was to investigate the effects of different straw returning modes on soil bacterial and fungal community structure and their relationships to soil organic carbon (SOC) fractions at three different soil depths (0–20, 20–40, and 40–60 cm) in a dryland under maize cultivation in Northeast (NE) China. SM, SP, and SG treatments significantly increased SOC content. Compared with SM and SP treatments, SG treatment significantly increased the content of SOC and easily oxidizable carbon (EOC) in the topsoil (0–20 cm depth), and increased dissolved organic carbon (DOC) and SOC content of the light fraction (LFOC) in the 20–40 cm layer. Meanwhile, SG treatment exhibited the highest microbial biomass C (MBC) content in all of the three soil depths. SG treatment also enhanced bacterial richness as well as fungal richness and diversity in the upper 40 cm of soil. In addition, SG treatment increased the relative abundance of Proteobacteria in all depths, and had the highest relative abundance of Basidiomycota in the first 20 cm of soil. SP treatment showed the lowest soil organic carbon content in all fractions and soil microbial community composition. SM treatment exhibited similar results to SG treatment in SOC, DOC, and LFOC contents, and bacterial diversity in the topsoil and subsoil. As a whole, treatment SG improved soil quality and maize yield, hence we recommend returning granulated straw as the most effective practice for enhancing labile SOC fractions as well as maintaining soil diversity and microbial richness of arid farmlands in NE China. [ABSTRACT FROM AUTHOR]

The application of agricultural wastes to the soil does not only improve soil fertility but also helps in the recycling of agricultural waste resources. However, the effects of agricultural organic materials on soil physicochemical properties in primary saline and alkaline lands unsatisfactory. In this study, the effects of different organic materials on the physicochemical properties of primary saline-alkali soil were studied in the west of Jilin province for two consecutive years. The organic materials included: grass (FG), sheep manure (SM), coarse corn straw (CS), and granular corn straw (GS). Soil pH, EC, total salt content, CEC, exchangeable sodium, ESP, organic matter, field capacity, water immersed bulk density, sedimentation coefficient, hardness and the morphological characteristics of soil aggregates were measured by conventional methods. CEC, SOM, and the physical properties varied significantly among the different treatments, whereas pH, EC, total salt content and exchangeable sodium did not. Moreover, the morphology of the organic materials significantly affected pH, EC1 : 5, total salt content, SOM and physical properties of the soil however, it did not affect the CEC, exchangeable sodium and ESP. Comparing granular corn straw with coarse corn straw, granular corn straw increased the SOM and field capacity by 48.5 and 17.0% respectively and decreased the pH, EC1 : 5, total salt content, water immersed bulk density, sedimentation coefficient and soil hardness by 2.6, 2.4, 3.7, 11.3, 6.2 and 7.7% respectively. In conclusion, the application of organic materials effectively improved the physical and chemical properties in the saline-alkali soil however did not cause a complete change in the saline-alkaline nature of the soil. The morphology of the organic materials also significantly affected soil properties, with granular corn straw having a better effect than the other treatments. [ABSTRACT FROM AUTHOR]