耕作方式对土壤水分入渗、有机碳含量及土壤结构的影响

为探明不同耕作方式对土壤剖面结构、水分入渗过程等的作用机理,采集田间长期定位耕作措施(常规耕作、免耕、深松)试验中的原状土柱(0~100 cm)及0~10 cm、10~20 cm、…、90~100 cm环刀样、原状土及混合土样,通过室内模拟试验进行了0~100 cm土层土壤入渗过程和饱和导水率的测定,分析了不同土层的土壤有机碳含量、土壤结构特征及相互关系。结果表明:从土柱顶部开始供水(恒定水头)到水分全部入渗到土柱底部的时间为:常规耕作免耕深松;土柱土壤入渗速率和累积入渗量为:深松免耕常规耕作;土柱累积蒸发量为:常规耕作免耕深松。土壤的饱和导水率表现为:0~10 cm和50~60 cm土层,免耕深松常规耕作;20~50 cm和60~100 cm土层,深松免耕常规耕作。随土层的加深,0.25 mm水稳性团聚体含量和土壤有机碳含量均表现为先增加(10~20 cm)再降低的趋势。在0~40 cm土层和80~100 cm土层,均以深松处理0.25 mm水稳性团聚体含量最高。在60 cm以上土层,土壤有机碳含量表现为:免耕深松常规耕作,而60 cm土层以下土壤有机碳显著降低,均低于4 g·kg?1,且在70 cm以下土层,常规耕作免耕深松。综上,耕作措施能够改变土壤有机碳含量,改善土壤结构,促进土壤蓄水保墒;深松更利于水分就地入渗,而免耕则更利于有机碳的提升和水分的储存,其作用深度在0~60 cm土层。

Effect of tillage method on soil water infiltration, organic carbon content and structure

Long-term tillage can greatly influence the physical properties of soil profile.For example,subsoiling and no-tillage can increase soil organic matter content,improve soil structure,increase the stability of soil structure and thereby improve soil moisture environment.In addition,no-tillage and subsoiling rotation can significantly improve soil water storage.Most reported studies were on no-tillage with mulching or subsoiling with mulching or no-tillage and subsoiling rotation.And the investigated soil profiles were usually focused on the ploughed layer.However,the effect of long-term subsoiling or no-tillage without mulching on the physical properties,infiltration processes,organic carbon distribution and structure of soil,especially for the deep soil has been rarely reported.Thus the objective of the study was to explore the effects of long-term no-tillage,subsoiling and conventional tillage,all without mulching,on the structure and water infiltration processes of the soil profile.An undisturbed 0-100 cm soil column,and the ring-cut samples of undisturbed soil and mixed soil samples of the 0-10 cm,10-20 cm,…,90-100 cm layers were collected in a long-term field experiment to determine the soil infiltration processes,saturated hydraulic conductivity,soil organic carbon content and soil structure.The results showed that the time for water infiltrating from the surface to the bottom of soil column under conventional tillage was longest among all treatments.The orders of permeability rate and cumulative infiltration of soil column were as follow:subsoiling ＞ no-tillage ＞ tillage.Then time for cumulative evaporation of the soil column arranged from max to min was from conventional tillage to no-tillage and then to subsoiling.Also the order of saturated hydraulic conductivity in the 0-10 cm and 50-60 cm soil layers was no-tillage ＞ subsoiling ＞ conventional tillage,and that in 20-50 cm and 60-100 cm soil layers was subsoiling ＞ no-tillage ＞ conventional tillage.With the increasing depth of soil,the content of ＞ 0.25 mm water-stable aggregates and soil organic carbon initially increased (10-20 cm layer) and then gradually decreased.In the 0-40 cm and 80-100 cm soil layer,the content of＞ 0.25 mm water-stable aggregates under subsoiling was highest.The order of soil organic carbon content in the 0-60 cm soil layer was no-tillage ＞ subsoiling ＞ conventional tillage.While soil organic carbon below the 60 cm layer of all the treatments was lower than 4.0 g·kg-1,and followed the order of conventional tillage ＞ no-tillage ＞ subsoiling below the 70 cm soil layer.It was therefore concluded that reasonable tillage improved soil organic carbon content and soil structure,and then promoted soil water conservation.Subsoiling was more favorable to soil water infiltration and no-tillage more conducive for organic carbon and water storage,especially in the 0-60 cm soil layer.