农田利用方式和冬灌对沙地农田土壤硝态氮积累的影响

研究了不同农田利用方式和冬灌对黑河中游边缘绿洲沙地农田土壤硝态氮（NO₃^--N）积累的影响.结果表明：不同农田利用方式0～300 cm土层NO₃^--N含量平均值介于1.27～83.60 mg·kg^-1;受土壤结构、施肥及灌溉的影响，NO₃^--N含量在0～40 cm和135～300 cm土层含量较高，40～135 cm土层含量较低;不同农田利用方式下的土壤剖面NO₃^--N含量差异极为明显，大棚蔬菜地各土层NO₃^--N含量均显著高于其他农田利用类型，土壤NO₃^--N累积量表现为大棚蔬菜地>番茄地>棉花地>制种玉米连作田>小麦-玉米轮作田>小麦/玉米间作田>苜蓿地>枣树园;大棚蔬菜地0～300 cm土层土壤剖面NO₃^--N累积量高达2171.45 kg·hm^-2，对地下水污染的威胁较为严重，番茄地和棉花地土壤剖面NO₃^--N累积量次之，粮田、苜蓿地和枣树园土壤剖面NO₃^--N累积量较小，但其污染潜力仍不容忽视.冬灌前后NO₃^--N含量随土壤层次表现出不同的变化规律，0～80 cm土层冬灌后NO₃^--N含量低于冬灌前，并且随灌溉量的增加NO₃^--N含量呈明显降低趋势;80～300 cm土层基本表现为冬灌后NO₃^--N含量高于冬灌前，且随灌溉量的增加NO₃^--N含量呈增加趋势;冬灌前后0～80 cm土层土壤剖面NO₃^--N的损失量基本为正值，80～300 cm土层基本为负值，并且随灌水量的增加表层土壤NO₃^--N损失量增大，表明冬灌是造成土壤累积的NO₃^--N向深层淋溶的主要原因.从减少淋溶和地下水污染的角度考虑，需要合理地调整土地利用方式，适当减少高NO₃^--N积累作物的种植，并确定合理的冬灌方式和灌水量.

Effects of farmland use type and winter irrigation on nitrate accumulation in sandy farmland soil.

With the sandy farmland in the marginal oasis in middle reaches of Heihe River Basin, Northwest China as test object, this paper studied soil NO3--N accumulation and leaching under effects of different farmland use type and winter irrigation. The results showed that the mean NO3--N concentration in 0〖KG-*2〗-〖KG-*7〗300 cm soil profile in different farmlands ranged from 127 mg·kg-1 to 8360 mg·kg-1. Soil NO3--N concentration was higher in 0〖KG-*2〗-〖KG-*7〗40 cm and 135〖KG-*2〗-〖KG-*7〗300 cm layers, but lower in 40〖KG-*2〗-〖KG-*7〗135 cm layer. Greenhouse vegetable field had a significantly higher soil NO3--N concentration than the other farmland use types. The accumulated amount of soil NO3--N decreased in the order of greenhouse vegetable field>tomato field>cotton field>seed maize field>maize-wheat rotation field>maize-wheat stripe intercropping field>alfalfa field>jujube plantation. The NO3--N accumulation in 0〖KG-*2〗-〖KG-*7〗300 cm soil profile in greenhouse vegetable filed reached 217145 kg·hm-2, which would be a serious menace to groundwater quality, followed by tomato field and cotton field. Lesser accumulation of soil NO3--N was found in seed maize field, maize-wheat intercropping field, maize-wheat rotation field, alfalfa field, and jujube plantation, but its pollution potential would not be neglected. After winter irrigation, soil NO3--N concentration decreased in 0〖KG-*2〗-〖KG-*7〗80 cm layer but increased in 80〖KG-*2〗-〖KG-*7〗300 cm layer, indicating that winter irrigation caused NO3--N leaching into deeper soil depth. The leached amount of soil NO3--N to deeper layers increased with increasing amount of winter irrigation. To mitigate soil NO3--N leaching and groundwater contamination, a comprehensive consideration should be made on the rational arrangement of farmland use type, proper decrease of planting N-accumulated crops, and reasonable winter irrigation.