长期施肥下黄壤性水稻土有机碳组分变化特征

Changes in Yellow Paddy Soil Organic Carbon Fractions Under Long-Term Fertilization

【目的】土壤有机碳具有高度异质性,不同组分的有机碳由于化学性质和存在方式等不同,其生物有效性和肥力功能不同,并反映出不同的稳定机制,所以深入研究土壤有机碳的组分特征,对于更好地了解土壤有机碳的稳定性和肥力机制具有重要意义。本研究以黄壤性水稻土为对象,旨在研究揭示长期施肥对土壤有机碳组分特征的影响并探讨合理培肥模式。【方法】以中国黄壤性水稻土18年长期施肥定位试验为依托,通过田间取样和室内分析,采用土壤有机碳物理-化学联合分组方法,重点研究不同施肥条件下土壤有机碳组分含量及分配比例的变化,并通过定量分析组分碳含量与年均碳投入量的关系,探讨土壤有机碳饱和现象。试验处理包括不施肥对照(CK)、单施化肥(NPK)、单施有机肥(M)、无机肥配施低量有机肥(0.5MNPK)和无机肥配施高量有机肥(MNPK),碳投入梯度为0.87—6.02 t·hm-2·a-1。【结果】与不施肥(CK)相比,单施化肥(NPK)处理显著增加了土壤游离态粗颗粒有机碳、化学保护粉粒组有机碳和生物化学保护粉粒组有机碳含量,总有机碳提升10%;有机肥处理(0.5MNPK、M、MNPK)显著增加了土壤游离态粗颗粒有机碳、物理保护有机碳、化学保护粉粒组、黏粒组有机碳和生物化学保护粉粒组、黏粒组有机碳,增加幅度高于化肥处理,总有机碳提升24%—46%,其中以有机无机肥配施(MNPK)的提升幅度最大;与不施肥(CK)及单施化肥(NPK)处理相比,有机肥处理(0.5MNPK、M、MNPK)土壤物理保护有机碳的分配比例显著升高;模型分析发现,长期施肥条件下土壤游离态粗颗粒有机碳浓度与年均碳投入量呈显著的线性关系,而化学保护态有机碳浓度与生物化学保护态有机碳浓度以及土壤总有机碳含量,均与年均碳投入量呈显著的"饱和曲线效应"的对数函数关系。【结论】有机无机肥配施是提升黄壤性水稻土有机碳水平的最佳培肥措施,并以物理保护有机碳的提升幅度最大,强化了有机碳的物理稳定机制;黄壤性水稻土较稳定的有机碳组分(化学保护态、生物化学保护态)以及总有机碳存在饱和现象,在当前条件下出现饱和限制。

【Objective】 Soil organic carbon represents an high heterogeneity. Because of different chemistry and existing forms, soil organic carbon fractions show different decomposibility and fertility functions. Therefore, investigating soil organic carbon fractions is important for better understanding the stabilization and fertility mechanims of soil organic carbon. This study was conducted in order to examine the effects of long-term fertilization on yellow paddy soil organic carbon fractions and to guide proper fertilization. 【Method】 An 18-year paddy field experiment was conducted to investigate the effects of long-term fertilization on soil organic carbon fractions and allocation, and also to discuss the soil organic carbon saturation phenomenon by quantifying the relationship between soil carbon levels with annual carbon inputs under different fertilizer treatments. The designed treatments were： no fertilizer control（CK）, chemical fertilizer（NPK）, organic manure（M）, low application rate of manure combined with chemical fertilizer（0.5MNPK） and high application rate of manure combined with chemical fertilizer（MNPK）. The average annual carbon inputs ranged from 0.87（in CK treatment） to 6.02 t·hm-2·a-1（in MNPK treatment）. 【Result】 The results showed that compared with CK, soil total organic carbon content was significantly increased by 10% under the NPK treatment, and by 24%-46% under the manuring treatments（0.5MNPK/M/MNPK）. Compared with CK, soil free coarse particulate carbon, chemically-protected silt carbon and biochemically-protected silt carbon contents were significantly increased under the NPK treatment, and soil free coarse particulate carbon, physically-protected carbon, chemically-protected silt and clay carbon and biochemically-protected silt and clay carbon contents were significantly increased under the manuring treatments（0.5MNPK/M/MNPK）. The proportion of physically-protected carbon to total carbon was higher under the treatments of 0.5MNPK, M and MNPK than under the CK and NPK trteatments. Soil free coarse particulate carbon concentration showed a significant linear increase with mean annual carbon input. Soil chemically-protected and biochemically-protected carbon concentrations and soil total carbon content showed a significant ＂saturation curve＂ increase with mean annual carbon input. 【Conclusion】 The data from the experiment indicate that the combined manure and chemical fertilizer is the best option for increasing the paddy soil organic carbon content, and that the relatively passive soil organic carbon fractions（chemically-protected, biochemically- protected） and total organic carbon existed saturation phenomenon and saturation limit under current conditions.