长期保护性耕作提高土壤大团聚体含量及团聚体有机碳的作用

Impact of long-term conservation tillage on soil aggregate formation and aggregate organic carbon contents

【目的】团聚体形成被认为是土壤固碳的最重要机制。本文以河南豫西地区长期耕作试验为研究对象,研究了长期保护性耕作对土壤团聚体性质及土壤有机碳(SOC)含量的影响,为探讨土壤固碳机理,优化黄土高原坡耕地区农田耕作管理措施,实现土壤固碳减排、培肥土壤提供理论依据。【方法】长期耕作试验开始于1999年,试验处理有免耕覆盖(NT)、深松覆盖(SM)和翻耕(CT)。利用湿筛法筛分第3年(2002年)和第13年(2011年)0—10cm和10—20 cm土层中,】2000、250~2000、53~250和【53μm级别的水稳性团聚体,计算团聚体平均质量直径(MWD),并测定了各级别团聚体的有机碳(SOC)含量。【结果】1)连续13年免耕覆盖和深松覆盖显著提高了土壤表层0—10 cm的SOC含量,分别比翻耕增加了33.47%和44.48%。2011年免耕覆盖和深松覆盖SOC含量较2002年上升了1.92%和8.59%,翻耕下降了18.97%。2)与翻耕相比,免耕覆盖和深松覆盖】2000μm团聚体含量显著提高了40.71%和106.75%;53~250μm团聚体含量显著降低了19.72%和22.53%;团聚体平均质量直径显著提高了20.55%和39.68%,显示了土壤结构的明显改善。3)免耕覆盖和深松覆盖显著提高了表层土壤所有团聚体有机碳的含量,尤其以】2000μm团聚体提升最多。与翻耕相比,】2000μm团聚体有机碳分别提高了40.0%和27.6%。4)免耕覆盖和深松覆盖下表层土壤大团聚体有机碳含量随耕作年限增加,微团聚体有机碳随耕作年限降低。】2000μm的土壤团聚体有机碳含量2011年较2002年分别升高了23.93%和7.12%,53~250μm微团聚体有机碳含量分别下降了19.58%和13.27%。【结论】长期保护性耕作(包括免耕覆盖和深松覆盖)可显著提高表层土壤大团聚体含量,降低微团聚体含量,提高团聚体的水稳性,改善土壤结构。同时可增加土壤团聚体有机碳含量,提高土壤肥力。长期保护性耕作在河南豫西丘陵地区是一种较为合理的耕作方式。

【Objectives】Conservation tillage is widely applied as its function in improving soil organic carbon( SOC) contents and the stabilization of soil aggregation. The objectives of this study were to reveal changes of SOC and soil aggregate organic carbon under long- term tillage systems,the influences of different tillage treatments on the formation of different sizes of aggregates,and the sustainable tillage system for the loess hilly region of China.【Methods】A long- term tillage experiment,started in 1999,was used for the study. The tillage treatmentsincluded: no- tillage( NT),sub- soiling and mulch tillage( SM),and conventional tillage( CT). Soil samples were collected at depths of 0-10 cm and 10-20 cm in 2002 and 2011,soil aggregates were separated into > 2000μm,250-2000 μm,53-250 μm and < 53 μm using wet sieving method. The SOC concentrations were measured by potassium bichromate titrimetric method. 【Results】The tillage treatments affect SOC contents more significantly in surface soil( 0-10 cm) than in sub- surface( 10-20 cm). Compared with CT,SOC contents in the 0-10 cm soil layer are significantly increased by 33. 47% and 44. 48% in the NT and SM treatments after 13 years,respectively. Compared with 2002,the SOC contents in NT and SM in 2011 are increased by 1. 92% and 8. 59%respectively,while that in CT decreased by 18. 97%. The NT and SM play a role in improving soil structure which could improve the contents of soil macroaggregates and water stability of aggregate in surface soil. Compared with CT,the contents of water- stable macroaggregates( > 2000 μm) in NT and SM are significantly increased by 40.71% and 106. 75% respectively,and the soil aggregate mean weight diameters( MWD) by 20. 55% and 39. 68%respectively,while the contents of microaggregates( 53-250 μm) are significantly decreased by 19. 72% and 22.53% respectively. NT and SM significantly improve soil aggregate organic carbon contents in surface soil,especially those in macroaggregates of > 2000 μm in size. Compared with CT,the organic carbon contents in macroaggregates of > 2000 μm in NT and SM are significantly increased by 40. 00% and 27. 60%.Macroaggregates organic carbon contents in NT and SM are increased with time,and microaggregates organic carbon contents are decreased reversely. Macroaggregates( > 2000 μm) organic carbon contents in the year of 2011 in NT and SM are increased by 23. 93% and 7. 12% respectively compared with the year of 2002,and microaggregates( 53- 250 μm) organic carbon contents in NT and SM are decreased inversely by 19. 58% and 13. 27%.【Conclusions】The long- term no- tillage and sub- soiling and mulch tillage,significantly improve surface soil structures through increasing water- stable macroaggregates contents, and improve aggregate organic carbon contents in all sizes aggregates. The macroaggregates organic carbon contents in the conservation tillage are increased with the elongation of experiment,these might explain the higher SOC content in the conservation tillage.In conclusion,the long- term conservation tillage improves soil structure along with SOC content and is a more sustainable tillage system for the loess hilly region of China.