岩溶地区不同土地利用方式下土壤斥水性的空间变化

以广西桂林市农业科学院大豆、甘蔗及梨树植被覆盖的土壤为例,研究不同土地利用模式下土壤斥水性的空间变化。通过对每个试验区面积为135 m×105 m的100个测量点应用滴水穿透时间法(water drop penetration time,WDPT)进行土壤斥水性测量,利用土壤含水量确定干旱(0.062±0.025)cm~3·cm~(-3)、中等(0.151±0.045)cm~3·cm~(-3)和湿润(0.237±0.086)cm~3·cm~(-3)的土壤水分条件。运用地统计方式,对土壤斥水性进行空间变化分析。结果表明:在干旱和湿润水分条件下,WDPT的大小均表现出梨树地最大,甘蔗地次之,大豆地最小,与土壤含水量和有机质大小的变化一致,但是在中等水分条件下,WDPT均值大豆地高于甘蔗地,同时3个试验区的滴水入渗持续时间都达到最大。土壤斥水性的地统计分析结果表明,在3种水分条件下,3个试验区的空间结构比基本上大于75%,空间相关性较强。在土壤斥水性的高阈值空间分布上,甘蔗地的稳定性比大豆地强,而梨树的空间分布稳定性最弱。研究结果说明人类的活动会对土壤斥水性空间稳定性产生干扰,但土壤本身仍具有恢复其空间分布稳定性的能力。     

干湿循环对土壤斥水性的影响

处于地表的各类土壤总是处于不断的干湿循环过程,土壤性质也会因此而发生改变。本文通过试验对干湿循环过程中斥水性土壤的"斥水–亲水"特性展开研究,试验结果表明:干湿循环对斥水性土壤的接触角及斥水性有重要影响。在干湿循环过程中,增湿时的初始状态不同则其初始接触角会发生变化,土壤斥水性对初始状态的敏感性随着黏粒含量的增加而增大。干湿循环开始时,土壤越干则初始接触角越大。当黏土和黏壤土试样含水量减小时,增湿或脱湿过程中滴水穿透时间(waterdroppenetrationtime,WDPT)先增加后减小,在某一时刻达到峰值,试样含水量相同时,脱湿过程所对应的WDPT要明显小于增湿过程,两种类型的土样在干湿循环中均没有临界含水量。随着含水量的降低,壤质砂土的WDPT是不断增加的,且干湿循环过程中斥水性砂土并没有出现峰值,存在明显的临界含水量。     

Water repellency reduction using soil heating in infiltration ponds of a wastewater soil aquifer treatment (SAT)

Reuse of treated wastewater (TWW) for irrigation in agriculture is a common alternative water source in arid regions suffering from fresh water (FW) shortage. Soil aquifer treatment (SAT) is frequently used for advanced TWW purification. Infiltration rates of water through the soil can decrease as a consequence of organic matter (OM) accumulation and the consequent induction of water repellency. In this research, soil heating to high temperatures was examined for its efficiency in OM content reduction and increased infiltration. In a laboratory experiment conducted using a hand burner and a combustion oven, water repellency was found to be reduced following increased heating temperature or heating duration, directly resulting in reduction of OM level. Chemical analysis of OM extracted from the heat treated soils revealed reduction in hydrophobic substances as a consequence of increased temperatures by soil heating and heating duration. In model ponds built to simulate large infiltration basins, OM content was reduced as a result of intensive and moderate soil heating in comparison to the untreated pond. However, no reduction in water repellency and only slight changes in infiltration rate were found as a consequence of soil heating. The differences in results obtained in the laboratory and the field experiments were probably related to the fact that the soil in the field experiment has been continuously reloaded with TWW containing OM.