秸秆还田对盐渍土团聚体稳定性及碳氮含量的影响

以黄河三角洲典型盐化潮土为研究对象,分析了3种盐渍化程度(轻度、中度、重度)和3 a连续秸秆还田下土壤水稳性团聚体组成、稳定性以及各级团聚体C、N含量的变化。研究结果表明:重度盐渍土0.25～2 mm和0.053～0.25 mm团聚体所占比例显著低于轻度和中度盐渍土;土壤盐分含量与0.25～2mm团聚体中有机碳和全氮的分配比例、0.053～0.25 mm团聚体中全氮的分配比例成显著负相关。秸秆还田使轻度盐渍土平均重量直径(MWD)、几何平均直径(GMD)和0.25 mm团聚体所占比例(R0.25)分别增加47.6%、39.7%和54.0%,使中度盐渍土MWD、GMD和R0.25分别增加31.0%、31.9%和31.4%;各粒级中秸秆还田使轻度盐渍土0.053～0.25 mm粒级有机碳和全氮含量增加最多,增加比例分别为29.1%和28.8%,该粒级中C、N分配比例也显著提高;秸秆还田使中度盐渍土0.25～2 mm团聚体有机碳及其分配比例提高最多,比例分别为56.1%和58.7%。秸秆还田对轻度和中度盐渍土团聚体的稳定性均起到了明显的改善作用,但不同盐渍土秸秆还田对土壤团聚体C、N分布的影响明显不同。

Effects of straw returning on saline soil aggregate stability and its carbon, nitrogen contents

Soil aggregate is the physical foundation of soil fertility and straw returning is widely recognized as an effective method to facilitate soil aggregate formation and stabilization. However, it is still unclear what effects of straw returning might have on soil aggregate composition and its carbon (C) as well as nitrogen (N) distribution in saline soils. In this study, taking the typical salinized fluvo-aquic soil of the Yellow River Delta as research object, we analyzed the water-stable aggregate composition, stability and the organic carbon (SOC), total nitrogen (TN) content of each aggregate in soils under three salinization degrees (light, moderate, highly) and after 3-year straw returning. Results showed that the proportions of 0.25-2 mm and 0.053-0.25 mm aggregates in highly-salinized soil were significantly lower than that in light-salinized soil and moderate-salinized soil (p < 0.05). The soil total salt content was negatively correlated with the contribution rates of 0.25-2 mm aggregates to SOC and TN, while it was negatively correlated with the contribution rates of 0.053-0.25 mm aggregates to TN. Straw returning induced a 47.6%, 39.7% and 54.0% increase in mean weight diameter (MWD), geometric mean diameter (GMD) and the content of macro-aggregates (R0.25) respectively for light-salinized soil, and a 31.0%, 31.9% and 31.4% increase in the corresponding indexes for moderate-salinized soil, respectively. For bulk soil, straw returning increased SOC and TN contents by 20.2% and 20.0% respectively for light-salinized soil, and increased SOC content by 35.2% for moderate-salinized soil. For SOC content in soil water-stable aggregates, straw returning for light-salinized soil increased SOC content by 22.7%, 29.1% and 21.9% in <0.053 mm, 0.053-0.25 mm and >2 mm aggregates, respectively, while increased that by 15.8%, 16.1%, 56.1% and 36.8% respectively for moderate-salinized soil with increasing particle size of soil aggregates. For SOC distribution in soil aggregates, the proportion of SOC in <0.053 mm aggregates decreased by 18.3% and 21.5% for light- and moderate-salinized soils, respectively, after 3-year straw returning; 0.053-0.25 mm aggregates of light-salinized soil had the highest increase (by 33.2%) in the contribution rate to SOC, while 0.25-2 mm aggregates of moderate-salinized soil had the highest increase (by 58.7%) in that among all aggregates. For TN content in soil water-stable aggregates, straw returning for light-salinized soil induced a 18.4% and 21.2% decrease in TN content in >2 mm aggregates and 0.25-2 mm aggregates respectively, and led to a 28.8% increase in TN content in 0.053-0.25 mm micro-aggregates. However, straw returning in moderate-salinized soil significantly decreased by 62.1% of the TN content in 0.053-0.25 mm micro-aggregates and increased by 1.1 times that in <0.053 mm aggregates. For TN distribution in soil aggregates, the contribution rate of <0.053 mm aggregates to TN decreased by 43.9% and that of 0.053-0.25 mm aggregates increased by 33.6% for light-salinized soil, while the contribution rate of <0.053 mm aggregates to TN increased by 0.9 times and that of 0.053-0.25 mm aggregates decreased by 50.9% for moderate-salinized soil. Overall, straw returning significantly improved the soil aggregate stability under light- and moderate-salinized soils, but it showed different effects on soil aggregate C, N distribution in different salinized soils, which might be attributed to the distinct formation mechanisms of soil aggregate under different salt contents.