【作者】 程冬兵；

【导师】 蔡崇法；

【作者基本信息】 华中农业大学 ， 土壤学， 2008， 博士

【摘要】 季节性干旱与水土流失并存是目前三峡库区面临的重要生态问题之一,等高绿篱技术是目前国内外广泛采用的一种坡耕地植被恢复和水土流失控制新技术,是库区农业生态系统持续发展的有效途径。本研究围绕等高绿篱坡地农业系统紫色土水分特性为主要内容,从土壤水形态学和土壤水动力学两方面展开研究,揭示等高绿篱影响下的坡地土壤水分有效性、土壤水分入渗性能、以及其空间分布特征,确定不同质地紫色土水动力学参数,探讨土壤水动力学参数间接推求方法在紫色土上的适用性,根据所获得资料通过物理模型和数学方法模拟等高绿篱篱前淤积土特殊剖面构造的土壤水分入渗过程。(1)选择新银合欢、黄荆和马桑三种绿篱,探讨其水土保育功效及抗旱效益。结果显示,由于绿篱的层层拦截,10年左右的时间,土坎高度增至近80cm,减缓坡度20°左右,具有显著的拦沙淤土效益;与对照相比,栽种绿篱后,土壤有机质增加52%-65%,土壤容重减小14%-17%,尤其是非毛管孔隙增幅达66%-124%,等高绿篱模式下土壤保肥增肥效益显著,土壤结构改善明显;按等高绿篱模式增加有效土层60cm计算,新银合欢、黄荆和马桑三个处理增加土壤水总库容分别为271mm、257mm和247mm,有力增强了土壤的抗旱性能。(2)以等高绿篱(新银合欢和黄荆)篱前淤积土为研究对象,评估等高绿篱坡地农业系统不同土层深度、不同距篱的土壤水分及物理性质变化特征。结果表明,绿篱处理土壤非毛管孔隙度、饱和入渗率、饱和含水量和自然含水量均高于石坎梯田处理,而土壤容重均小于石坎梯田处理,尤其在表层二层其差异更明显,等高绿篱保育土壤效益显著;同一土层,随距篱(坎)延长,绿篱处理土壤容重、自然含水量逐渐增大,土壤非毛管孔隙、饱和入渗率和饱和含水量逐渐减小,而石坎梯田处理变化不明显;随土层加深,各处理土壤容重、自然含水量均相应逐渐增大,土壤非毛管孔隙、饱和入渗率和饱和含水量均相应逐渐减小,且处理之间差异也逐渐缩小;距篱远近间接反映了绿篱处理对土壤水分及物理性质影响程度,距篱越近,影响越大。新银合欢处理与黄荆处理之间相比,效应相当。(3)以等高绿篱(新银合欢和黄荆)前淤积土与石坎梯田为研究对象,探讨不同土层深度、不同距篱(坎)的土壤水分入渗特性及其影响因素,并对其土壤水分入渗过程进行模型拟合。结果显示,同一土层,随距篱(坎)延长,各处理土壤入渗性能坎依次减弱,不同距篱绿篱处理土壤入渗性能存在较大差异,而不同距坎石坎梯田处理土壤入渗性能差异相对不明显;随土层加深,绿篱处理土壤入渗性能相应逐渐减弱,而石坎梯田处理土壤入渗性能急剧减弱;对于表层土壤平均入渗性能,石坎梯田处理优于绿篱处理,而对于二层土壤平均入渗性能,绿篱处理转而优于石坎梯田处理,三层土壤,各处理土壤入渗性能基本相当;黄荆处理土壤入渗性能存在明显的空间变化规律,主要通过水平和垂直两个方向来体现,其中水平方向,距篱远近间接反映了黄荆对土壤入渗性能的影响程度;土壤容重、砂粘比与有机质对土壤入渗性能均有显著影响,而初始含水量仅对初始入渗率有显著影响,其中砂粘比对初始入渗率、前30分钟入渗量影响最大,容重对稳定入渗率影响最大;Green-Ampt模型和Philip模型更适合本研究土壤水分入渗过程描述与模拟,且具有较高准确性。(4)选择等高绿篱新银合欢篱前淤积土、石坎梯田及自然荒坡的表层紫色土,室内测定水动力学参数。结果表明,对于紫色土水分特征曲线,土壤含水量与土壤水吸力呈负相关关系。同一土壤水吸力水平下,细质土的持水量最高,粗质土的持水量最小。Gardner模型和Van Genuchten模型均可用于描述紫色土水分特征曲线;对于紫色土水分扩散率,土壤水分扩散率与土壤含水量呈正相关关系。随含水量增加(θ＞0.25),不同质地土样水分扩散率差异愈大,粗质土＞细质土。已有经验模型均可用于表达紫色土水分扩散率函数关系;对于紫色土导水率,土壤导水率与土壤含水量呈正相关关系。同一含水量水平,粗质土导水率大于细质土。幂函数模型、Brooks-Corcy模型和Mualem-Van Genuchten模型均可用于表达紫色土导水率关系。(5)室内通过水平一维吸渗试验和土壤水分再分布试验,结合土壤颗粒分析等物理实验,探讨间接推求紫色土非饱和导水参数的适用性。结果显示,通过建立的土壤水分特征曲线模型分形维数与土壤粒径分布分形维数关系式,结合Tyler-Wheatcraft模型进行土壤水分特征曲线预测,预测值与实测值具有良好的一致性;简单入渗法和入渗特性法推求的水动力学参数中,水分特征曲线准确性较好,水分扩散率和非饱和导水率准确性较差;根据土壤水分再分布过程推求紫色土的水分扩散率与实测值具有良好的一致性,但推求的非饱和导水率与计算值均有很大的出入。然而单一的土壤水分垂直或水平再分布过程结合实测水分特征曲线推求的非饱和导水率与计算值基本相当,准确性均很高。另外,该方法比较适合低湿土壤的非饱和导水参数推求。(6)在(4)和(5)的基础上,首次推导了等高绿篱篱前淤积土特殊剖面构造的土壤水分入渗模型,并通过室内模拟进行准确性验证。结果显示,对于均质土剖面入渗,粗质地的湿润锋随时间推进速度快于细质地。而对于不同质地剖面入渗,一定剖面入渗设置条件下,粗质土半剖面的垂直湿润锋随时间推进速度快于细质土。而且,对于粗质地,上细下粗三角形剖面层次的垂直湿润锋随时间推进速度快于上粗下细,但对于细质地,差异不明显;无论上粗下细,还是上细下粗,不同剖面层次对斜面湿润锋变化曲线影响不大;各剖面层次入渗,湿润锋、入渗速率与时间均呈极显著幂函数关系;建立的紫色土特殊剖面构造入渗模型,经实测值验证,模拟值与实测值具有极好的一致性,充分说明模型的可靠性和准确性,均可用于描述紫色土特殊剖面构造的入渗过程。同时,建立的入渗模型可与经验模型相互转换,具有很好的相通性,模型参数也具有一定的物理意义。更多还原

【Abstract】 The coexistence of seasonal drought and soil and water losses is one major ecological problem in the three gorges reservoir area now.Contour hedgerow is a very common and effective technique around the world,which is often employed to revegetate on cultivated slope land and conserve water and soil resources.And it is also considered as an available way of sustainable development of agroecosystem in the three gorges reservoir area.Soil water properties under contour hedgerow-intercroping system were studied thoroughly in two respects of soil water morphology and soil water dynamics.The purpose of this research was to discover soil water availability,soil permeability,and theirs spatial variability,as well as to determine hydraulic parameters of different textural purple soils and to discuss methods of estimating hydraulic parameters indirectly in term of applicability on purple soils.On the basis of former research,process of water infiltration in special soil profile was simulated according to alluvial soils in front of hedges through physical models and mathematical methods.The main results were as follows:(1) Three hedges of Leucaena leucocephala,Vitex negundo and Coriaria sinica were selected to discuss the benefits of soil and water conservation and drought-resistance.The results showed that because of trapping and depositing by contour hedgerows,the height of silt had increased to 80cm and the gradient had been eliminated 20°after 10 years, which reflected that the effect of sediment trapping and depositing was significant Compared with the control,within the contour hedgerow treatments,soil organic matter increased from 52%to 65%,soil bulk density decreased from 14%to 17%,and soil non-capillary porosity increased from 66%to 124%especially.The effects of fertilizer maintenance and improvement under the contour hedgerow system were significant and soil structure was improved obviously.According to the effective thickness of soil layer of 60cm,soil water total volumetric capacity in the treatments of Leucaena leucocephala, Vitex negundo and Coriaria sinica increases 271mm,257mm and 247mm respectively, which then improves the soil ability of drought-resistance greatly.(2) Alluvial soils in front of hedges(Leucaena leucocephala and Vitex negundo) were taken as the objects,to evaluate the effects on soil water and physical properties from different distances to hedgerows at different soil depths by contour hedgerow-intercroping system.The results showed that soil non-capillary porosity, saturated hydraulic conductivity,saturated water content and natural water content in the hedgerows treatments were higher than in the rock ridge terrace treatment,while the soil bulk density in the hedgerows treatments was lower than in the rock ridge terrace treatment,which reflected that the effects on water and soil conservation by hedgerows were significant,especially in the top and second layer.Based on the same depth,with the extending of the distance to hedgerows(ridge),in the hedgerows treatments soil bulk density and natural water content increased gradually,and soil non-capillary porosity, saturated hydraulic conductivity and saturated water content decreased gradually,while no apparent change in the rock ridge terrace treatment.With the deepening of the soil layer,in each treatment soil bulk density and natural water content increased gradually, and soil non-capillary porosity,saturated hydraulic conductivity and saturated water content decreased gradually accordingly,and their differences among treatments were also lessened gradually.The distance to hedgerow reflected the degree of effects on soil water and physical properties by hedgerow indirectly.The closer to hedgerow,the greater the effects were.Comparing treatments of Leucaena leucocephala and Vitex negundo, their effects were equivalent.(3) Alluvial soils in front of hedges(Leucaena leucocephala and Vitex negundo) and rock ridge terrace were taken as the objects,to study the soil water infiltration properties and theirs factors from different distances to hedges/ridge at different soil depths,as well as fit the model of the soil infiltration process.The results showed that,based on the same depth,with the extending of the distance to hedgerows(ridge),soil infiltration properties represented the trend of decreasing gradually for all treatments,and there was big difference among different distances to hedges for hedgerow treatments but no difference among different distances to ridge for rock ridge terrace treatment.With the deepening of the soil layer,soil infiltration properties decreased gradually for hedgerow treatments, while decreased rapidly for rock ridge terrace treatment.In the top layer the average soil infiltration properties for rock ridge terrace treatment was better than those for hedgerow treatments,but in the second layer the average soil infiltration properties for hedgerow treatments were better than those for rock ridge terrace treatment on the contrary,and in the third layer,they were equivalent.There was clear space variation in vertical and horizontal directions of soil infiltration properties for Vitex negundo treatment.In horizontal direction,the distance to hedgerow reflected the degree of effects on soil water and physical properties by Vitex negundo indirectly.Bulk density,sand/clay ratio and OM had significant influence on all of soil infiltration properties,but initial soil water content only had significant influence on initial infiltration rate.Sand/clay ratio had the most effect on initial infiltration rate and infiltration in 30min,and bulk density had the most effect on stable infiltration rate.Infiltration models of Green-Ampt and Philip were more suitable for describing and simulating the soil infiltration process in this research with higher accuracy.(4) Top purple soils of alluvial soil in front of Leucaena leucocephala,rock ridge terrace and natural slope were taken to measure hydraulic parameters in laboratory.The results were as follows,for purple soil water retention cuvre,there was a negative correlation between soil water suction and soil water content.Under the same soil water suction,water content of fine soil was the highest,and water content of coarse soil was the lowest.Both Gardner model and Van Genuchten model could be used to describe purple soil water retention curve.For purple soil water diffusivity,there was a positive correlation between soil water diffusivity and soil water content.With the increase of water content(θ＞0.25),the difference among different textural soils became more obvious(coarse soil＞fine soil).The existing models could be used to express purple soil water diffusivity.For purple soil conductivity,there was a positive correlation between soil conductivity and soil water content.Under the same water content,conductivity of coarse soil was higher than fine soil.Power function,Brooks-Corey model and Mualem-Van Genuchten model could be used to express purple soil conductivity.(5) Through conducting experiments of horizontal one-dimension infiltration,soil water redistribution and soil particle analysis,indirect approaches of determining soil unsaturated hydraulic conductivity and diffusivity were discussed,in term of applicability on purple soils.The results showed that,based on the linear function between the fractal dimension of soil particle size distribution and the fractal dimension of soil water retention curve,soil water retention curve was predicted through Tyler-Wheatcraft’s model.It was quite obvious that the predicted soil water retention curve agreed well with the measured data.Hydraulic parameters were estimated by simple infiltration method and horizontal infiltration method.The estimated soil water retention curve was accurate,while the accuracy of estimated soil water diffusivity and conductivity was poor.Based on soil water redistributions,the estimated purple soil water diffusivity was in good agreement with the measured,but the estimated purple soil conductivity deviated greatly.While,the purple soil conductivity to be estimated agreed well with the calculated,by combining one-dimension redistributions of soil water and the measured soil water retention curve. In addition,this method was more suitable for the low soil moisture.(6) On the basis of research(4) and(5),models of water infiltration in special soil profile were derived according to alluvial soils in front of hedges for the first time,and verificated by laboratory simulation.The results showed that in homogeneous soil profile, wetting front rate for coarse soil was faster than free soil.But in heterogeneous soils profile,under the same boundary conditions,vertical wetting front rate of half part profile of coarse soil was faster than fine soil.Furthermore,vertical wetting front rate of half part profile of coarse soil in triangular profile with fine upper and coarse lower was faster than in triangular profile with coarse upper and fine lower.But there was no difference for half part profile of fine soil.There was no significant effect on incline wetting front rate by heterogeneous soils profile,whether coarse upper and fine lower,or fine upper and coarse lower.There was a very significant power relationship between wetting front,infiltration rate and time for different soil profiles.The established infiltration models for special profile of purple soils were verified by experimental data,and the results indicated that the estimated agreed well with the observed.It was suggested that these models be reliable and reasonable,so that these models could be used to express the infiltration process in special profile of purple soils.Meanwhile,there was well consistency between the established infiltration models and the existing empirical models,and they could be transformed each other.Moreover,parameters of established theoretical models had some certain physical meaning.更多还原