【作者】 李凯；

【导师】 徐学选；

【作者基本信息】 西北农林科技大学 ， 草学， 2021， 硕士

【摘要】 土壤斥水性(Soil Water Repellency,SWR)在世界范围内普遍发生。我国黄土高原地区在实行退耕还林还草工程以来,土壤的基本性质和结构特征得到了显著改善。然而黄土土壤利用多样化、黄土高原气候变化会强化SWR,进而会干扰降雨入渗过程,需要对区域SWR发生机制、影响因素等进行研究。试验选择黄土旱塬长武县农田试验场的黑垆土(玉米地和苜蓿地)、鄂尔多斯砂黄土(草地和沙棘地)共4个土地利用样地,采集0-20 cm土层土样,对2种土壤类型的4种土地利用的土样设计4水平土壤含水量、3水平土壤容重和3水平十八烷基伯胺(OCT)添加量进行组合试验,用滴水穿透时间(WDPT,water drip penetration time)法进行斥水时间测试,躺滴法进行斥水角度测试。通过相关性分析及建立回归模型,分析各因素对SWR的影响程度,结合土壤质地、土壤有机质含量、土壤团聚体等差异探究黄土母质发育下的黑垆土、砂黄土在不同土地利用影响下发生斥水的条件。取得的主要结果有:(1)在滴水穿透试验中,黑垆土土壤在一般情况下表现出亲水性,低水和高OCT添加量组合下会出现斥水。黑垆土中OCT添加量、土壤含水量对SWR的影响明显大于土壤容重的影响。而在砂黄土土壤,含水量对斥水性的影响最大。在不同土地利用下的土壤含水量、OCT添加量之间对SWR也存在极显著交互作用,土壤容重仅仅会有微弱交互影响。在黑垆土,苜蓿地较玉米地有机碳含量大,其本身易积累极性而有斥水潜能;在砂黄土土地上,草地和沙棘地因其有较高的砂粒含量,在低水条件下也会有更大的斥水可能发生。(2)土壤含水量和OCT添加量对于4类样地土壤斥水角度的影响:随着土壤含水量(在0-6%含水量范围)增加、OCT添加量的增加,“土-水”接触角均有增大的趋势。同时存在土地利用间的差异:除玉米地在4%土壤含水量时表现出最大“土-水”接触角,苜蓿地、草地和沙棘地最大“土-水”接触角均在6%土壤含水量。玉米地、苜蓿地在2%土壤含水量时表现出最小“土-水”接触角,草地、沙棘地最小“土-水”接触角均在0%土壤含水量;黑垆土的玉米地、苜蓿地较砂黄土的草地、沙棘地的趋势性稍显不足。(3)两个土壤由亲水到轻微斥水转变必要条件:黑垆土的玉米地和苜蓿地出现斥水的条件和具体的WDPT值较为接近。黑垆土在加入0.10%OCT添加量后,在0%-6%的低水条件下可以表现出斥水性,而且斥水程度随着含水量增加有增强趋势。砂黄土的草地和沙棘地出现斥水的条件和具体的WDPT值较为接近。砂黄土无水条件处理后的土壤无斥水性,在加入0.025%OCT添加量后,在2%-6%的低水条件下可以表现出斥水性,而且斥水程度随着含水量增加有先增强后减弱的趋势。(4)除玉米地外,其他3类样地的WDPT值和“土-水”接触角度均表现出显著的正相关关系。滴水穿透时间和“土-水”接触角在表征SWR时有一定的互相参考作用,WDPT值以单水珠入渗的持续时间体现入渗的难以程度,“土-水”接触角从水珠与土壤表层接触的角度大小反映了土壤发生斥水时的强度。研究结果表明,黄土地区由于气候、土壤质地、耕作方式的不同,引起土壤发生SWR的外在和内在因素也复杂多样,导致不同区域的黄土在发生斥水时的影响因素也不相同。影响黑垆土SWR的因素中OCT添加量、土壤含水量的影响明显大于土壤容重的影响。在砂黄土中,由于OCT添加量相对黑垆土降低、土壤含水量对斥水性的影响变得更大。黑垆土的农地有机碳含量高,加上粘粒含量也高,容易结合成团聚体而变得具有更强的斥水性。砂黄土草地和沙棘地的气候更加干燥,尽管土壤有机质含量低、但有较高的砂粒含量,在低水条件下也会有一定的斥水风险。因此在降水入渗的过程中,应注意黄土不同土地利用下的土壤基本性质变化对黄土斥水风险的影响。更多还原

【Abstract】 SWR(soil water repellency,SWR)occurs worldwide.Since the implementation of the project of returning farmland to grassland in the Loess Plateau of my country,the basic properties and structural characteristics of the soil have been significantly improved.However,the diversification of loess soil utilization and climate change in the Loess Plateau will intensify SWR,which in turn will interfere with the process of rainfall infiltration.It is necessary to study the mechanism and influencing factors of regional SWR.Helu soil(corn field and alfalfa field)and the Ordos sandy loess(grassland and Hippophae rhamnoides land)in the farmland test field of Changwu in the Loess Plateau were selected as the sample plots.All plots were dug at 0-20 cm in the field to get soil samples,and then the samles had been handled as the 4 levels of soil moisture content,3 levels of soil bulk density,and 3 levels of octadecylamine(OCT)addition amount,which meet to the combination the design of 4 soil samples of 2 soil types and 4 land uses.The dripping penetration time method was used for the water repellency time test,and the lying drip method was for the water repellency angle test.Through correlation analysis and the established regression models,the degree of influence of various factors on SWR,included the differences in soil texture,soil organic carbon content,soil aggregates,etc.had been analyzed.The occurrence condition of water repellent of Helu soil and sand loess had been discussed.The main results obtained:(1)In the drip penetration test,the Heilu soil does not show water repellency under normal circumstances,and water repellency will appear under low water content and high OCT additions.The influence of OCT addition and soil moisture content on SWR in Helu soil was significantly greater than that of soil bulk density.In sandy loess soil,the influence of water content is greater.At the same time,there is a very significant interaction between the soil moisture content and OCT addition under different land uses on SWR,and the soil bulk density could only act much weak interaction.On Helu soil,the alfalfa field has higher organic carbon content than the corn field.It is easy to accumulate polarity and then potentially to repel water.On the sandy loess soil,the grassland and Hippophae rhamnoides land have higher sand content,which the lower water repellency may also occur under dry soil conditions.(2)The effect of soil moisture content and OCT addition amount on the SWR angle of the four types of plots is: as the soil moisture content(in the range of 0-6% water content)increases,the increase in OCT addition will led the soil-water contact angle to increase.At the same time,there are differences in land use: except for the corn field that exhibits the largest soil-water contact angle when the soil moisture content is 4%,the largest soil-water contact angle of alfalfa field,grassland and Hippophae rhamnoides land is all at 6% soil water content.The amount of water.Corn fields and alfalfa fields show the smallest "soil-water" contact angle at 2% soil water content,and grassland and Hippophae rhamnoides land have the smallest "soil-water" contact angles at 0% soil moisture content;corn fields in Helu soil,The trend of alfalfa land is slightly less than that of sandy loess grassland and Hippophae rhamnoides land.(3)The necessary conditions for the two soils to change from hydrophilic to slightly water-repellent: the water-repellent conditions of corn field and alfalfa field in Helu soil were closer to the specific WDPT value.After adding 0.10% OCT,Helu soil could show water repellency under low water conditions of 0%-6%,and the water repellency has a tendency to increase with the increase of water content.The water-repellent conditions of sandy loess grassland and Hippophae rhamnoides land are close to the specific WDPT value.The sandy loess soil is non-water-repellent after treatment under water-free conditions.After adding 0.025% OCT,it can show water-repellency under low water conditions of 2%-6%,and the degree of water-repellency increases with the increase of water content.The tendency to weaken after being strengthened.(4)Except for the corn field,the WDPT value and the "soil-water" contact angle of the other three types of plots all show a significant positive correlation.The penetration time of dripping water and the "soil-water" contact angle are related to the characterization of SWR.The WDPT value reflects the duration of the single droplet infiltration when the soil is water-repellent,and the "soil-water" contact angle reflects the strength of the soil when water-repellency occurs.The results of the study show that due to differences in climate and farming methods,the loess area produces different levels of soil development.The soil texture is different in the region.The external and internal factors of SWR in the soil are also complex and diverse,resulting in loess in different regions.The influencing factors in the occurrence of water repellency are also different.Among the factors that affect the SWR of Helu soil,the influence of OCT addition and soil moisture content is significantly greater than the influence of soil bulk density.In sand loess,due to the lower OCT addition to Helu loess,the influence of soil water content on water repellency becomes greater.Helu soil has higher organic carbon content and higher clay content,which is easy to combine into agglomerates and become more water repellent.The climate of sandy loess area where grassland and Hippophae rhamnoides land is drier,although the soil organic carbon content is lower,but higher in sand content,a certain degree of water repellency may occur under low water conditions,and there is a stronger risk of water repellency compare with Heilu soil.Therefore,attention should be paid to the process of precipitation infiltration when soil water repellency exist.The risk of water repellency of loess under climate changes should therefore be counted in and some mitigating methods need to be take in the future.更多还原