Increasing cropland soil carbon (C) sequestration and improving crop nitrogen use efficiency (NUE) are vital for sustainable agriculture and environmental protection. The incorporation of straw and application of straw-derived biochar to croplands may help to achieve these goals; however, the long-term effects on soil C sequestration and NUE in double-rice cropping systems are poorly understood. Here, a 6-y field experiment was conducted in a double-rice cropping system to investigate the variations in soil C sequestration and NUE with straw and straw-derived biochar amendments. The treatments were as follows: control with zero nitrogen (N0); conventional chemical fertilizer application (NPK); NPK plus 3 t rice straw dry matter (DM) incorporated per ha⁻¹ season⁻¹ (NPK + LS); NPK plus 6 t rice straw DM incorporated per ha⁻¹ season⁻¹ (NPK + HS); NPK plus 24 t straw-derived biochar DM incorporated per ha⁻¹ (NPK + LC) applied once; and NPK plus 48 t straw-derived biochar DM incorporated per ha⁻¹ (NPK + HC) applied once. Both the straw and biochar additions increased the soil C content in the topsoil, and the NPK + LC treatment sequestered 2.6-fold more soil C than the NPK + HS treatment over the 6-y period, when the input amounts of straw as well as the straw derived C were similar for both treatments. Besides input C directly into the fields, biochar application also increased soil original organic C accumulation in the NPK + LC treatment. Compared with NPK, 50 % and 100 % straw incorporation to the field increased the mean NUE by 22.3 % and 39.8 %, respectively, in the late rice season of 4–6 y, mainly due to increasing soil organic C. Rice grain yields decreased in the early rice season for the first 3 y of the straw treatments but increased in the first season when the biochar was applied, when compared with NPK. However, in the second 3 y after straw application, the grain yield of NPK + HS was significantly higher than that of NPK in late rice season. This investigation has indicated that biochar application had a higher potential in soil carbon sequestration than straw incorporation, and long-term (> 3 y) straw incorporation favored for the enhancement of NUE in paddy fields.

增加农田土壤碳（C）的固存和提高作物氮的利用效率（NUE）对于可持续农业和环境保护至关重要。将秸秆并入秸秆生物炭到农田中可能有助于实现这些目标；然而，人们对双季稻种植制度对土壤固碳和NUE的长期影响了解甚少。在这里，在双水稻种植系统中进行了6年田间试验，以研究秸秆和秸秆衍生的生物炭改良剂对土壤固碳和NUE的影响。处理如下：用零氮（N0）控制；用零氮（NO）控制。常规化肥施用（NPK）; 每公顷^-1季节^-1掺入的氮磷钾加上3吨稻草干物质（DM）（NPK + LS）；每公顷^-1季节^-1施用的NPK加6吨稻草DM （NPK + HS）；每公顷^-1（NPK + LC）加入NPK加24吨秸秆衍生的生物炭DM，施用一次；每公顷^-1掺入NPK和48吨秸秆衍生的生物炭DM（NPK + HC）应用一次。秸秆和生物炭的添加都增加了表层土壤中的土壤碳含量，并且在秸秆输入量和输入量的6年内，NPK + LC处理比NPK + HS处理的土壤碳吸附量高出2.6倍。两种处理的秸秆衍生碳相似。除了将碳直接输入田间，生物炭的施用还增加了NPK + LC处理中土壤原始有机碳的积累。与NPK相比，稻田4-6 y时，稻田秸秆掺入量分别为50％和100％，平均NUE分别增加22.3％和39.8％，这主要是由于土壤有机碳增加。水稻籽粒产量下降与NPK相比，秸秆处理的前3年在稻作的早期稻米季节，但施用生物炭的第一个季节在稻米季节增加。然而，秸秆还田后的第3年，NPK + HS的籽粒产量明显高于水稻后期的NPK。这项研究表明，生物炭的施用比秸秆还田具有更高的土壤固碳潜力，长期（> 3 y）秸秆还田有利于提高稻田的NUE。