土壤有机碳(SOC)作为土壤肥力形成的基础,不但影响土壤质量及功能,而且在全球气候变化中扮演重要角色。近30年来,中国农田施肥、耕作、秸秆还田等农业管理措施经历了巨大变化,然而,从国家尺度上来说,这些变化对中国农田SOC时空变化的影响及主要驱动因子的贡献仍不明晰。

针对这些问题,在中科院先导专项及国家自然科学基金等的资助下,南京土壤所联合中科院沈阳生态所、地理资源所、水保所、亚热带农业生态所、成都山地所等科研院所,以及南京农业大学、西南大学等高校,通过1980及2011年两个时段SOC实测数据及其对应点位管理措施实地调查数据的系统分析,发现中国农田表层SOC由1980年的28.56 t C/ha增加到了2011年的32.90 t C/ha,净增幅4.34 t C/ha,作物根系、秸秆及其它(主要是有机肥)碳输入变化对SOC增幅的贡献分别为30%、40%和30%,为中国农田土壤总体固碳提供了直接证据。

进一步从影响农业管理决策的经济和政策因素角度阐释了国家尺度农田SOC时空变化的驱动力,发现在中国农田相对较低初始SOC含量的背景下,2000年之前,作物增产经济效益驱动的化肥投入增加而导致的作物根系生物量增加是碳输入的主要影响因子,而2000年后,秸秆还田政策大规模推广导致的土壤碳输入增强则占支配地位,从而揭示了经济和政策驱动的碳输入增强是近30年来中国农田SOC累积的主要原因。并发现化学N肥过量输入及耕层变浅是未来可能限制中国农田土壤固碳的主要因子,为我国进一步优化农业管理措施、实现土壤固碳及肥力提升双赢战略提供了依据。

上述研究成果于2018年4月17日发表于美国国家科学院院刊PNAS.

Zhao YC, Wang MY, Hu SJ, Zhang XD, Ouyang Z, Zhang GL, Huang B, Zhao SW, Wu JS, Xie DT, Zhu B, Yu DS, Pan XZ, Xu SX, Shi XZ. Economics- and policy-driven organic carbon input enhancement dominates soil organic carbon accumulation in Chinese croplands. PNAS, doi: 10.1073/pnas.1700292114

Abstract

China’s croplands have experienced drastic changes in management practices, such as fertilization, tillage, and residue treatments, since the 1980s. There is an ongoing debate about the impact of these changes on soil organic carbon (SOC) and its implications. Here we report results from an extensive study that provided direct evidence of cropland SOC sequestration in China. Based on the soil sampling locations recorded by the Second National Soil Survey of China in 1980, we collected 4,060 soil samples in 2011 from 58 counties that represent the typical cropping systems across China. Our results showed that across the country, the average SOC stock in the topsoil (0–20 cm) increased from 28.6 Mg C ha−1 in 1980 to 32.9 Mg C ha−1 in 2011, representing a net increase of 140 kg C ha−1 year−1. However, the SOC change differed among the major agricultural regions: SOC increased in all major agronomic regions except in Northeast China. The SOC sequestration was largely attributed to increased organic inputs driven by economics and policy: while higher root biomass resulting from enhanced crop productivity by chemical fertilizers predominated before 2000, higher residue inputs following the large-scale implementation of crop straw/stover return policy took over thereafter. The SOC change was negatively related to N inputs in East China, suggesting that the excessive N inputs, plus the shallowness of plow layers, may constrain the future C sequestration in Chinese croplands. Our results indicate that cropland SOC sequestration can be achieved through effectively manipulating economic and policy incentives to farmers.