高量秸秆不同深度还田对黑土有机质组成和酶活性的影响

在田间耕作条件下黑土3个土层(0~20、20~40、40~60cm)添加4%和8%高量玉米秸秆于尼龙袋中原位培养近4年后,研究不同层次土壤秸秆转化与有机碳积累特征,以及腐殖质各组分和土壤酶活性的变化。结果表明,添加4%的秸秆量0~20、20~40和40~60cm土层有机碳分别增加31.8%、96.4%和171.1%,8%秸秆添加量分别增加了86.2%、193.5%和265.9%,增加秸秆还田深度有利于土壤有机碳的积累。0~20 cm土层在无秸秆还田情况下有机碳下降了29.3%,而20~40 cm土层仅下降了1.8%。土壤有机碳含量和酶活性均随秸秆添加量的增加而提高,腐殖质胡敏酸/富里酸(HA/FA)比值发生较大变化,改善了腐殖质品质。各处理腐殖酸碳(HS-C)和胡敏酸碳(HA-C)的大小为20~40 cm土层0~20 cm土层40~60 cm土层,而40~60 cm土层则更有利于富里酸碳(FA-C)的积累。土壤过氧化氢酶活性、脲酶和蔗糖酶活性分别与HA-C、FA-C含量呈极显著正相关、显著正相关。研究结果为深层秸秆还田促进土壤有机质的积累提供了理论依据。

Effect of incorporation of crop straw on composition of soil organic matter and enzyme activity in black soil relative to depth and rate of the incorporation

Soil organic matter, as a basic substance of soil fertility, is not only a major source of soil nutrients, but also a critical factor controlling soil physic-chemical properties, biological properties and various fertility factors. In China and other countries, soil organic matter in farmland is maintained and raised mostly through incorporation of crop straw. Humification processes of the straw incorporated, and accumulation of organic carbon, composition of soil humus and soil enzyme activities varied sharply between soils different in depth of straw incorporation, and also between soils different in straw incorporation rate. To verify the effects of depth and rate of straw incorporation on these factors. a field experiment was carried out in a tract of farmland of black soil. In the field experiment, corn stalk packed at a rate of 40g/kg and 80g/kg soil in nylon bags was buried into three soil layers different in depth (0 ~ 20, 20 ~ 40 and 40 ~ 60cm) for 4 years of in situ incubation for monitoring variations of corn stalk transformation, organic carbon accumulation, humus composition and soil enzyme activities. Results show that the addition of 40g/kg soil of the straw increased organic carbon by 31.8%, 96.4% and 171.1%, respectively, at the 0 ~ 20, 20 ~ 40 and 40 ~ 60cm soil layers,, and the addition of 80g/kg soil of the straw did by 86.2%, 193.5% and 265.9 %, respectively; demonstrating that depth of the incorporation is conducive to soil organic carbon accumulation, because poor aeration in deep soil layers slows decomposition and transformation of the straw, thus favoring humus accumulation. However, in control (no straw incorporated), organic carbon declined by 29.3% in the 0 ~ 20cm soil layer, but only by 1.8% in the 20 ~ 40cm soil layer . The reason is that soil enzyme activity is higher in the shallow soil layer than in the deep soil layer, and hence, soil humus mineralization rate is much higher in the former than in the latter. Higher straw incorporation rate (80g/kg soil) increased soil organic carbon and soil enzyme activity. As a result humus HA / FA ratio in the soil changed greatly, towards improving humus in quality. Accumulation of humine acid carbon (HS-C) and humic acid carbon (HA-C) varied with soil depth, exhibiting a decreasing order of 20 ~ 40cm > 0 ~ 20cm > 40 ~ 60cm, while accumulation of fulvic acid carbon (FA-C) in the 40 ~ 60cm soil layer was more prominent. The contents of HA-C and FA-C were in extremely significant positive relationship with catalase activity and in significant positive one with urease and invertase activities. The above-listed findings suggest that incorporation of a high amount of straw may quickly increase soil organic carbon content, and deeper incorporation contributes to accumulation of organic carbon. Straw incorporation also alters soil humus composition and promotes activities of catalase, urease and invertase. For comparison, after the four years of experiment, the control was found to be much lower in soil organic matter content in the surface layer, which indicates that renewal of soil organic matter in farmland is very important to maintenance of soil fertility.