2001—2010年中国农作物可还田量的时空演变

作物收获后的地上秸秆和地下根系部分是农田土壤有机质的主要来源。准确估算农作物收获残余物(CSRE)可归还到农田中的生物量可以帮助认识秸秆和根系在农田土壤碳循环中的作用。本文采用2011—2012年全国实测水稻、小麦、玉米、大豆、油菜、棉花6种作物的生物量获得的干燥系数(DC)、收获指数(HI)和根冠比(R/S)，结合2001—2010年以县为单位的农业统计数据估算了可归还到农田中的农作物收获残余物生物量。2001—2010年中国农田产生的CSRE总量为3.5 Pg C。6种作物种，水稻产生的CSRE总量最多，为106.4 Tg C，玉米年均增加量最大，为C 6.5 Tg/a。2001—2010年，以县级行政单元估算的单位面积CSRE值在0.01~9.32 t/(hm2·a)之间变动，全国平均值为C 3.20 t/(hm2·a)。农田产生的CSRE空间分布不平衡，黄淮海区、长江中下游区和西南区的四川盆地CSRE可还田量较高。2001—2010年间，全国大部分地区农田产生的CSRE量呈增加趋势，黄淮海区、长江中下游地区中北部、四川盆地和东北地区上升趋势明显，且CSRE年际波动较小。华南地区农作物CSRE量减少趋势明显，但是年际波动较小。CSRE量波动较大的区域主要是西北地区。农田产生的CSRE量与气温和降水有相关关系，但是不显著。

Spatial-temporal patterns of CSRE of crops in China during 2001-2010

In agricultural soils, the plant-derived input of carbon(C) from above- and belowground harvest residues and rhizodeposition (CSRE) is major source of soil organic matter. Thus, precise estimations of the harvest residues is important to monitor the supply of SOC in agricultural soils and model its future development under a changing climate. In this study, a new data bank of dry coefficient (DC), harvest index (HI), and root to shoot ratio (R/S) for rice, wheat, corn grain, soybean, cotton, and oilseed crops based on field samples collected across China from 2011 to 2012 was used. Combined with the information of county-level crop yield reported as national agricultural statistics, the amount of CSRE produced in 2001–2010 was estimated, and its spatial distribution was analyzed. The results showed that total 3.5 Pg C was produced in 2001–2010 in China’s cropland, mainly distributed in the Huanghuaihai region, the middle-lower reaches of Yangtze river and Sichuan basin of China. The mean county-level CSRE density was C 3.20 t/(hm2·a), ranging from C 0.01 to 9.32 t/(hm2·a). For the change of CSRE during 2001–2010, most counties had an ascending tendency. The Huanghuaihai region, north and middle part of the middle-lower reaches of Yangtze river, Northeast China and Sichuan basin showed obvious ascending tendencies with small annual fluctuation. The south of China showed an obvious descending tendency but also with the small annual fluctuation. The climate factors such as mean annual temperature and precipitation had no significant correlation with CSRE in China. The agroecosystem was greatly affected by human activities such as the cultivation method, cropping system and chemical fertilizer input.