中文摘要：

【目的】阐明长期施肥下土壤有机碳演变规律及碳库组分变化,揭示黄土旱塬土壤固碳效应及培肥模式。【方法】利用32年作物产量和土壤有机碳（SOC）数据分析土壤碳投入、固定及演变特征,采集2010年土样样品,通过物理分组方法得到砂粒、粗粉粒、细粉粒、粗黏粒、细黏粒及大团聚体和微团聚体,分析施肥对碳库组分的影响。【结果】试验中总碳投入从不施肥（CK）的8.10 t C hm^-2增加到秸秆还田（SNP）的69.40 t C hm^-2,耕层土壤SOC贮量施肥之间相差1.82倍,增施有机肥（M、MNP）SOC为21.76—24.04 t C hm^-2,SNP为16.01 t C hm^-2;土壤SOC贮量随碳输入量的增加而提高,有机碳固定率25.80%—36.05%,而秸秆还田只有8.20%;除长期不施肥处理仅靠根茬投入维持稳定的SOC水平外,其余所有肥料处理SOC均随试验年限延长而增加,SNP、M、MNP处理固碳速率依次为0.246、0.326、0.361 t C hm^-2 a-1。MNP和SNP处理砂粒SOC是CK的3.85和2.94倍、N处理的2.41和1.84倍,MNP处理较CK、NP处理SOC总量只增加了32.50%、18.10%,而砂粒中SOC却提高了285.12%、105.74%,砂粒级有机碳对施肥最敏感。施肥提高了活性有机碳（POC）与矿物结合态有机碳（MOC）的比率（W）,MNP、M、SNP处理的W值达18.62%、16.24%、14.41%,单施氮肥（N）和氮磷配施（NP）仅9.11%、9.99%,施肥提高了有机碳活性,改善了土壤有机碳质量。不施肥大团聚体（〉250μm）SOC是微团聚体（〈53μm）的9.14倍,施肥提高了15.83—23.84倍,并提高了大团聚体中土壤C/N比,而对微团聚体C/N影响不大。尽管团聚体含碳量随团聚体粒径增加而增加,但微团聚体有机碳含量增加对土壤固碳速率的作用显著高于大团聚体,对土壤碳的固定与物理保护起着重要作用。【结论】长期增施有机肥、秸秆还田提高了黄土旱塬黑垆土的碳固定与积累,且固碳增量主要分布在砂粒和大团聚体中。因此增施?

英文摘要：

[ Objective ] The objective of this study was to clarify the effect of long-term fertilization on soil organic carbon （SOC） changes and carbon fraction differences, and to reveal C sequestration and soil fertility improvement model of fertilization, in Cumulic Haplustoll of Loess Plateau in China. [Method] Grain yields and SOC recorded from a 32-year dryland fertilization trial with six fertilizations were used to estimate C input and sequestration and SOC trends, and soil samples in the 32nd year taken from the experiments were separated into sand, coarse silt, fine silt, coarse clay, fine clay, and aggregates by physical way, and the content and distribution of SOC in these particle-size fractions and aggregates were analyzed. [Result]Cumulative C input ranged from 8.10 t C.hm^-2 for the unfertilized treatment （CK） to 69.40 t C-hm^-2 for the treatment that received straw （S） plus inorganic N added annually and P fertilizers added every second year （SNP）, and there was a difference of 1.82 times in SOC stock in the 0-20 cm soil layer among the fertilizer treatments and SOC stock was 21.76, 24.04, 16.01 t C.hm^-2 in the M, MNP, SNP treatments in 2010. SOC stock increased with cumulative C input, C sequestration into SOC rate ranged from 25.80% to 36.05% but 8.20% from straw and root in the SNP, suggesting manure and root residues is more effective in building soil C than straw, SOC significantly built up with time except the CK, in which SOC remained almost stable by root resides C in input only, and annual soil-C sequestration rates （slopes for linear regression of SOC relate to time） were 0.246, 0.326, and 0.361 t C.hm^-2.a1 for the SNP, M, and MNP treatments respectively. SOC in the sand fraction for the MNP and SNP were 3.85 and 2.94 times higher than that for CK, and 2.41 and 1.84 times higher than that for the N. Compared with the CK and NP, SOC in total soil for the MNP increased by 32.50% and 18.10%, but SOC in the sand increased by 285.12% and 105.74%, implying SOC in the sand was the