CT扫描技术研究有机物料还田深度对黑土孔隙结构影响

Effects of organic amendment depths on black soil pore structure using CT scanning technology

为了探明有机物料还田深度对土壤孔隙结构的影响,2019年玉米播种前在黑龙江海伦市的黑土上开展了田间定位试验,设置了秸秆浅混还田(0~15 cm)(T1)、秸秆深混还田(0~35 cm)(T2)和秸秆配合有机肥深混还田(0~35 cm)(T3)3个有机物料还田处理,以无秸秆还田常规耕作为对照(CK),4次重复,随机排列。玉米秸秆还田量为10000 kg/hm^(2),有机肥还田量为30000 kg/hm^(2)。2019年玉米收获后,采集原状土柱,利用CT扫描技术可视化土壤结构,量化土壤孔隙结构特征。结果表明,虽然有机物料还田仅一个玉米生长季,但是与CK处理相比,T1、T2和T3处理显著降低了0~15 cm土层容重,增加了饱和导水率和田间持水量(P<0.05);T2和T3处理显著改善了>15~35 cm土层的上述3个土壤物理指标。有机物料的施用增加相应土层的孔隙数量、改善了孔隙分布。与CK处理相比,T1、T2和T3处理0~15 cm土层>500μm孔隙数量和孔隙度分别显著增加了18.1%~179.9%和69.2%~256%(P<0.05);与其他处理相比,T2处理>15~35 cm土层>1000μm孔隙度显著增加了17.4%~196.2%(P<0.05)。有机物料还田增加了孔隙结构的复杂性,土壤中出现了交叉孔隙和细长孔隙,提高了孔隙的连通性。与CK处理相比,T1、T2和T3处理显著降低了0~15 cm土层欧拉数,T1处理显著增加了分形维数(P<0.05);秸秆或秸秆配施有机肥深混处理显著改善了>15~35 cm土层的土壤孔隙结构,与CK相比,显著增加了各向异性、分形维数和成圆率,显著减少了欧拉数(P<0.05)。欧拉数和>1000μm孔隙度分别对0~35 cm土层容重和饱和导水率贡献度最大,而各向异性和欧拉数分别对0~15 cm和>15~35 cm土层田间持水量贡献度最大,说明有机物料对土壤物理性质的改善作用是通过调控土壤孔结构,改善孔隙分布、增加孔隙的复杂性、连通性来实现的。

Soil structure is a key factor to determine the different functions of soil,such as water infiltration and retention,soil permeability,and nutrients availability.The dynamic behavior of soil also depends mainly on the tillage,crop roots,and soil organic matter return.Black soil is one of the most important arable soil with high clay content,but hard soil structure is one of the main factors limiting crop growth.It is still lacking on the effect of organic amendment on soil pore structure in the black soil.In this study,a field experiment was carried out in the black soil region located in Hailun City,Heilongjiang Province of China,in order to clarify the effects of organic amendment and depths on soil physical properties and pore structure before maize sowing in 2019.Four treatments were conducted using random block design with four replicates,including shallow tillage with maize straw return in 0-15 cm soil layer(T1),deep tillage with maize straw return(T2),or combined maize straw and organic manure return(T3)in 0-35 cm soil layer,conventional tillage without organic amendment as control.Maize straw and organic manure were also incorporated into the soil layers by shovel using manual work,where the application rates were 10000 and 30000 kg/hm^(2),respectively.CT scanning was adopted to visualize and quantify soil pore structure after maize harvesting.The constant head method was used to measure the saturated hydraulic conductivity.The results demonstrated that the bulk density under T1,T2,and T3 treatments significantly decreased 3.77%-5.66%,compared with CK,while the saturated hydraulic conductivity increased by 2.2-5.00 times,and the field water capacity increased by 6.91%-11.01%within 0-15 cm soil layer(P<0.05).T2 and T3 treatments also improved the bulk density,saturated hydraulic conductivity,and field water capacity within>15-35 cm soil layer after one maize growing season.Furthermore,the number of soil pores and porosity of>500μm aperture under T1,T2,and T3 treatments significantly increased by 18.1%-179.9%and 69.2%-256%(P<0.05)in 0-15 cm soil layer,respectively,compared with CK treatment(P<0.05).Specifically,the soil porosity of>1000μm aperture were more 17.4%-196.2%under T2 treatment than the rest.It infers that the treatments with organic amendment increased the number of soil pores with optimal distribution.In addition,the complexity and connectivity of soil pore also increased significantly,in presence of connected and sender pore.The Euler number values under T1,T2,and T3 treatments were decreased by 21.7%-54.3%,whereas,the fractal dimension under T1 treatment increased by 1.5%in 0-15 cm soil layer(P<0.05),compared with CK treatment.T2 and T3 treatments improved the soil pore structure in>15-35 cm soil layer,as shown in that the Euler decreased by 65.9%-70.5%,anisotropy and fractal dimension increased by 50.0%-110%,and 12.8%-13.9%,respectively,compared with CK treatment(P<0.05).The Euler and porosity of>1000μm aperture presented the largest contribution both for the bulk density and saturated hydraulic conductivity in 0-35 cm soil layer,whereas,the anisotropy and Euler presented the largest contribution for the field capacity in 0-15 cm and>15-35 cm soil layers.Pearson correlation analysis indicated that the extremely significant negative relationship was found between bulk density and saturated hydraulic conductivity,field water capacity,soil porosity within 0-15 cm soil layer(P<0.01),while the extremely significant or significant correlation was found between bulk density and all indicators,excepting for the anisotropy and Euler.Consequently,the improved physical properties of soil were attributed to the fact that the organic amendment regulated soil structure,including optimal distribution of soil pore,complex,and connectivity of pore structure.Correspondingly,the organic amendment can be expected to serve as an effective approach for the pore structure of black soil.It is also necessary to consider the response of soil pore structure in the decomposition of returned organic manure in the future.