摘要:为了探明耕作措施对陇中黄土高原旱作农田土壤有机碳的影响，以连续进行17年的不同耕作措施长期定位试验为研究对象，利用碘化钠重液分组法，探索了传统耕作（T）、传统耕作+秸秆还田（TS）、免耕（NT）、免耕+秸秆覆盖（NTS）4种耕作措施对陇中黄土高原旱作农田土壤游离态颗粒有机碳、闭蓄态颗粒有机碳、颗粒态有机碳和矿质结合态有机碳的影响。结果表明：土壤总有机碳含量随土层加深而降低，游离态颗粒有机碳、闭蓄态颗粒有机碳、颗粒态有机碳的含量和占土壤总有机碳的比例均随土层加深而降低，而矿质结合态有机碳含量和占土壤总有机碳比例则随土层加深而增加。在0～40 cm各土层，各处理土壤颗粒态有机碳占总有机碳的比例（54.02%～76.78%）均高于矿质结合态有机碳占总有机碳的比例（31.78%～46.11%）。较之T处理，TS和NTS处理均不同程度提升土壤游离态颗粒有机碳、闭蓄态颗粒有机碳、颗粒态有机碳的含量和占土壤总有机碳的比例，其中NTS处理的提升效果最显著，TS处理次之。虽然NT、TS、NTS处理可提升土壤矿质结合态有机碳含量，但T处理下的矿质结合态有机碳占总有机碳的比例高于NT、TS和NTS处理。耕作模式和秸秆添加模式均对土壤总有机碳、游离态颗粒有机碳、闭蓄态颗粒有机碳、颗粒态有机碳和矿质结合态有机碳的提升具有显著效应，但秸秆添加模式的效应高于耕作模式。同时，免耕模式仅对0～10 cm各土层土壤总有机碳的提升效应达到显著水平，对0～20 cm各土层土壤碳组分的提升效应均达显著水平，而添加秸秆对0～40 cm各土层土壤总有机碳和各组分均发挥着显著提升效应。综合来看，免耕配合秸秆还田可以提升土壤活力，促进土壤固碳，有利于该区构建环境友好型和可持续发展型农业生产模式。
Abstract:As a vital indicator of soil quality, soil organic carbon and its fractions play an essential role in soil productive capacity and crop yield, while may be affected by soil tillage methods in dry farmland areas. Organic carbon is a key component of soil because it carries many functions in agro-ecosystem. A study was carried out to investigate the effects of different tillage and straw application patterns on the distribution of soil particulate organic carbon fractions under spring wheat-pea rotation by using the density fraction method[NaI:(1.70±0.02) g·cm-3]. Four particulate fractions of soil total organic carbon (STOC), free particulate organic carbon (FPOC), occluded particulate organic carbon (OPOC), particulate organic carbon (POC) and mineral-associated organic carbon (MOC) were obtained. The study involved a 17-year local field experiment at the Rainfed Agricultural Experimental Station of Gansu Agricultural University, Dingxi, Gansu Province, China (35°28'N, 104°44'E). The experiment included four treatments, which were conventional tillage (T), no-tillage (NT), no-tillage with straw incorporation (NTS) and conventional tillage with straw mulching (TS) arranged in a complete randomized block design with three replications. The soil samples were taken at four different soil depths (0-5 cm, 5-10 cm, 10-20 cm and 20-40 cm) per plot. The results showed that the dominant fraction of STOC for each soil layer was POC (the ratio range was 54.02%-76.78%) in four treatments, and the main component of POC was OPOC, suggesting that the effect of physical protection was the crucial role for soil carbon sequestration and fixation in the area. The contents of STOC, FPOC, OPOC and POC were decreased with increasing soil layers, MOC content, however, was increased with increasing soil layers. FPOC/STOC, OPOC/STOC and POC/STOC were decreased with increasing soil layer, MOC/STOC was increased with increasing soil layers. In 0-40 cm soil depth, compared with treatment T, the mean values of STOC, FPOC, OPOC, POC and MOC in NT, TS and NTS treatments were greater, and NTS treatment exhibited the greatest effect. The same trend was represented for FPOC/STOC and POC/STOC. No tillage system represented significantly enhance effect on contents of FPOC, OPOC, POC and MOC in 0-20 cm soil depths, but the straw retention system showed significantly boosting effect on contents of STOC, FPOC, OPOC, POC and MOC in 0-40 cm soil depths, and F test values of straw retention were greater than that of tillage system, thereby the effects of straw retention were greater than that of tillage system. As a whole, NTS may be an ideal enhancer of farmland productivity in the semi-arid soil ecosystem through enhancing soil organic carbon pool which resulted in the maintenance of higher nutrient content, and subsequently helping in contributing sustainable agricultural development in the Loess Plateau of central Gansu Province.
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