采用间歇灌溉进行土壤盐分淋洗的适用性

为比较一次性灌溉和间歇灌溉在盐分淋洗效率方面的优劣,采用HYDRUS-1D两区模型模拟分析了不同频次灌溉条件下的土壤水盐运移过程。结果表明存在一个间歇灌溉具有更高淋洗效率的最大深度,并将其称为临界深度。对砂土的模拟显示在灌水总量为20 cm时,随着潜在蒸发强度从0 mm/d升高至6 mm/d,临界深度从60 cm以上降为0 cm;而在潜在蒸发强度为2 mm/d时,随着灌水总量从10 cm增加至40 cm,临界深度相应从20 cm增加至接近80 cm。比较而言,透水性好、不动水体占比高、两部分孔隙之间水分和溶质交换能力差的土壤,临界深度更大;对黏土、黏壤土、壤土、砂壤土和砂土分别进行模拟显示偏砂性土壤具有更大的临界深度,在灌水总量和潜在蒸发强度分别为30 cm和2 mm/d时,黏土和砂土的临界深度分别为56 cm和大于100 cm。总的来看,对于间歇灌溉是否能提高盐分淋洗效率不能一概而论,引入临界深度可以在一定程度上解释研究者们对于间歇灌溉是否能提高盐分淋洗效率的不同认识。

Feasibility of applying intermittent irrigation on solute leaching

In order to compare leaching efficiencies of continuous and intermittent irrigations, the HYDRUS-1D dual-porosity model was applied to simulate water and salt movement in soils under difference schemes of irrigation. Results showed that there was a critical depth above which intermittent irrigation would result in higher salt leaching efficiency. Simulations of sandy soils showed that when total irrigation amount was 20 cm, critical depth would decline from more than 60 cm to 0 cm as potential evaporation rate increased from 0 mm/d to 6 mm/d; but it would rise from 20 cm to almost 80 cm as total irrigation amount increased from 10 cm to 40 cm when potential evaporation rate was fixed to be 2 mm/d. Generally, soils with higher water conductivity, higher porosity of micro-pores and lower exchange rate of water and solute between micro and macro pores held higher critical depth, and simulations of sandy, loamy sandy, loamy, clayey loamy and clayey soils indicated that sandy soils were more likely to hold higher critical depth. When total irrigation amount was 30 cm and potential evaporation rate was 2 mm/d, critical depth of clay and sandy soil were 56 cm and more than 100 cm, respectively. In conclusion, there is no universal answer on whether intermittent irrigation would promote leaching efficiency, but critical depth could explain former contradict conclusions on this problem.