塔里木河下游灌区灌溉方式转变对农田及其防护林土壤水盐动态的影响

IMPACT OF CHANGES OF IRRIGATION PATTERN ON SALT-WATER DYNAMICS OF SOILS IN FARMLAND AND ITS SHELTERBELT IN THE IRRIGATED ZONE IN THE LOWER REACHES OF TARIM RIVER

通过分析塔里木河下游喀拉米吉镇绿洲大面积滴灌条件下的农田(3个棉田1个果园)与其防护林地土壤水盐分布特征,采用对比试验与野外监测方法,研究了当前滴灌体系对林网内农田及其防护林地的影响,分析防护林网内土壤水盐变化的主要因子。得出以下结论:(1)喀拉米吉镇绿洲,由于滴灌技术的普及,地下水埋深以0.5 m a-1的速度下降;地下水埋深具有季节性变化,在非灌溉季节地下水埋深较浅,在灌溉季节地下水埋深较深,与非灌溉季节相比,灌溉季节里地下水埋深平均下降了1 m以上。(2)由于喀拉米吉镇绿洲农田滴灌对土壤的影响深度不超过80 cm,灌溉水对地下水的补给量几乎为零,农田防护林根系只能从土壤深层吸收水分,导致了林地内土壤含水率显著低于农田(p<0.01)。(3)当前5 250 m3 hm-2 a-1的棉田灌溉、7 000 m3 hm-2 a-1的果园灌溉,使0～60 cm的土壤盐分处于低盐状态,基本达到农田的脱盐要求;防护林地盐分均明显高于农田(p<0.01),为农田的2倍～3倍;林地内土壤盐分表聚作用明显:砂壤土林地、砂土林地、黏土林地1、黏土林地2内表层土壤盐值分别较其农田高79.3%、77.1%、80.6%、88.4%。(4)通过林地间土壤含水率、土壤盐分的比较,发现地下水埋深的不同是农田防护林地土壤水盐差异的主要因素,150 cm土体内,含水率高的林地其含盐量也高,含水率低的林地其含盐量也低。

After comparative analysis of the distribution characteristics of soil water and salt in farmlands （3 cotton fields and 1 orchard） and their shelterbelts in drip irrigation prevailing Kalamiji Oasis in the lower reaches of Tarim River, Northwest China through comparative tests and field monitoring, effects of the current drip irrigation pattern on farmlands within forest networks and their shelterbehs and main factors affecting salt-water dynamics in the soil within the forest network were studied and analyzed with the following conclusions obtained. （ 1 ） In Kalamiji oasis, the groundwater table in the fields lowers at a rate of 0.5 m a-1 as a result of popularization of drip irrigation and varies seasonally; it is relatively shallow in non-irrigation season and relatively deep in irrigation season; and over 1 m deeper in the latter than in the former. （2） As the impact of drip irrigation on soil never goes deeper than 80 cm, the irrigation supplies little water, almost nil, to groundwater, while the roots of farmland shelterbelt have to go deep into the soil to absorb water, thus leading to significantly lower soil water content in the shelterbelt than in farmland （p 〈 0.01 ）. （3） The current irrigation rate, 5 250 m3 hm -2 a-1 in the cotton field and 7 000 m3 hm-2 a-1 in the orchard are adequate to keep the soil （0 -60 cm） low in salinity and basically satisfying the requirements of farmland desalination; but, in shelterbelt land soil salinity is obviously higher or 2 - 3 times higher than in farmland （p 〈 0.01 ） ; surface accumulation of soil salts is apparent; as a result, the conductivity is 79.3% , 77.1% , 80.6% and 88.4% higher in loamy forest land, sandy forest land, clayey forest land 1 and clayey forest land 2 than in farmlands, respectively. （4） Comparison in soil water and salt contents between shelterbelt lands shows that the difference in depth of the groundwater table is the main factor for difference in soil water and salt content and consequently, forest lands, high in water content, are high in salinity, and vice versa in the 0 - 150 cm soil layer.