长期免耕对不同土层土壤结构与有机碳分布的影响

摘要

为探明长期翻耕与免耕条件下不同土层深度土壤结构稳定性及其有机碳分布特征,在长期定位试验中分层(0 ～ 10 cm、10 ～ 20 cm、…、90 ～ 100 cm)采集免耕和常规耕作处理下混合土样和原状土样进行土壤结构与有机碳的测定,结果表明:①随着土层的加深,0.5 ～2.0 mm和大于2.0mm粒级团聚体含量表现为逐渐降低的趋势,而其他粒级团聚体含量呈增加趋势.免耕更利于提高大粒级团聚体(＞0.5 mm)的含量,且土壤结构的稳定性显著提高,其作用深度在50 cm以上.②随着土层的加深,土壤总有机碳和活性有机碳均表现为先增加后降低再趋于稳定的趋势.免耕处理在0 ～ 80 cm土层的土壤总有机碳和活性有机碳均高于常规耕作处理.③随着土层的加深,不同粒级团聚体总有机碳含量呈降低趋势,大粒级团聚体中含有较高的有机碳.免耕更利于0 ～40 cm土层不同粒级团聚体总有机碳含量的提高.随着土壤团聚体粒级的降低,土壤活性有机碳含量呈降低趋势.与常规耕作相比,除0.053 ～0.250 mm粒级团聚体外,免耕提高了0～ 20 cm土层各粒级团聚体中活性有机碳含量.④随着土层的加深,各粒级团聚体中有机碳对土壤总有机碳的贡献率表现为先降低后增加再降低的趋势.不同粒级团聚体中,大于2.0 mm和小于0.053 mm粒级团聚体有机碳贡献率在0～100 cm土层均低于其他粒级团聚体.在0～20 cm、30～ 40 cm和90～ 100 cm土层,免耕处理各粒级团聚体有机碳累积贡献率均高于常规耕作.%In order to investigate the stability of soil structure and the distribution characteristics of organic carbon in different soil depths (0 ～ 10 cm,10 ～ 20 cm,…,90 ～ 100 cm) under long-term conventional tillage and no-tillage conditions,mixed soil samples and undisturbed soil samples collected from no-tillage and conventional tillage treatments were designed to measure soil structure and soil organic carbon content.The results indicated that with the increase of soil depth,the contents of aggregates with diameter of 0.5 ～ 2.0 mm and greater than 2.0 mm were gradually decreased,while other particle agglomerates were increased.No-tillage treatment could improve the large aggregates (greater than 0.5 mm) content,and significantly improve the stability of soil structure,the effect of depth was more than 60 cm.With the increase of soil depth,soil organic carbon and active organic carbon content were increased firstly and then decreased,and then trended to be stable.Soil carbon and active organic carbon of notillage treatment in 0 ～ 80 cm soil layer were higher than that of conventional tillage.With the increase of soil depth,soil aggregates organic carbon content was decreased,while organic carbon content of large aggregates was higher than other size aggregates.No-tillage was more conducive to increase soil organic carbon content of different size aggregates under 0 ～ 40 cm soil depth.With the decrease of soil aggregates,soil active organic carbon content was decreased.Compared with conventional tillage,except 0.053 ～ 0.250 mm size aggregate,no-tillage increased active organic carbon content in 0 ～ 20 cm soil layer of various aggregates.With the increase of soil depth,the contribution rate of organic carbon to soil total organic carbon in different size fractions showed the trend of decreasing first,then increasing and then decreasing.In different aggregates,contribution rate of organic carbon of aggregates with diameter greater than 2.0 mm and less than 0.053 mm in the 0 ～ 100 cm soil layer was lower than those of other size aggregates.In 0 ～20 cm,30 ～40 cm and 90 ～ 100 cm soil layers,accumulation contribution rate of different aggregates organic carbon of no-tillage treatment was higher than that of conventional tillage.