Abstract:

【Objective】Understanding of the dynamics and mechanisms of organic materials in soil are essential for improving the utilization of organic wastes and developing nutrient management strategies in many intensive farming regions around the world. The objective of this study was to elucidate the decomposition characteristics of straw and manure in typical farmland soils in China.【Method】The field experiment was conducted in three soils (Red soil, Aquic soil, and Black soil) at the “National Soil Fertility and Fertilizer Effects Long-term Monitoring Network” experimental station. Four organic materials (wheat straw (WS), maize straw (MS), pig manure (PM) and cattle manure (CM)) were dried and then packed separately into 48 μm-mesh size nylon net bag. Each bag contained 20 g organic materials was cut into 2 mm pieces. Based on the temperature difference, each treatment was sampled 6 times within 49-360 days after landfill. We analyzed the change of organic carbon content with soil accumulated temperature and residual rate during decomposition to study the relative contribution of climate factors, organic material properties and soil nutrients in the decomposition rate of different organic materials.【Result】Humification coefficient of straw and manure were 11%-39% and 50%-57%, respectively, suggesting faster decomposition of straw than manure. The organic labile decomposable carbon pool accounted for 76% and 43% at straw and manure, respectively, while recalcitrant carbon pool accounted for 17% and 53%, respectively. The decomposition rates constants (k) of labile decomposable carbon pool were similar in straw and manure, with an accumulated turnover temperature (1/k) of 1 400-2 000℃. VPA (variance decomposition analysis) analysis showed that the nature of the organic material, contributing 28% to the variance, was the main influencing factor in its decomposition. Individually, the greatest contributor during the decomposition of straw was the combined interaction of climate, organic material properties and soil (42.3%). In contrast, the decomposition of manure was mainly controlled by the climate (38.3%).【Conclusion】The decomposition rate and proportion of labile decomposable carbon pool in straw were higher than that of manure. The decomposition of straw was influenced by the synergistic effect of climate, soil and material properties, while manure was influenced mainly by climate factors. It was critical to determine the returning time and returning amount of straw in the field in combination with the local hydrothermal conditions. Manure was recommended to be piled up along with proper timing of its application before returning to the field.

Key words: straw, manure, fraction of carbon remaining, climate, carbon pool