灌水器埋深对红壤区涌泉根灌双点源入渗水氮运移的影响

The Effects of Depth of Subsurface Dual Emitters in Surge-root Irrigation on Water and Nitrogen Movement inRed Soil

【目的】研究红壤区涌泉根灌双点源入渗土壤水氮运移分布规律,为提高涌泉根灌水氮利用效率和灌水器合理埋深提供理论依据。【方法】在大田通过灌水器埋深分别为30、45、60 cm的硝酸铵钙溶液入渗试验,研究了灌水器埋深对涌泉根灌双点源交汇入渗土壤的入渗能力、湿润锋运移距离、土壤水分以及铵态氮和硝态氮运移特性的影响,并建立了红壤涌泉根灌土壤累计入渗量及湿润锋运移距离与入渗历时的关系模型。【结果】灌水器埋深分别为30、45和60 cm时,红壤累计入渗量和稳定入渗率分别为18.84 L和0.035 cm/min、17.09 L和0.031 cm/min以及14.37 L和0.024 cm/min,即灌水器埋深越大,土壤的累计入渗量和稳渗率就越小,且累计入渗量与入渗历时之间均符合幂函数关系;灌水器埋深分别为30、45和60 cm时,交汇入渗发生的时间分别为168、187和197 min,交汇发生时间增幅依次为10.16%和5.56%,湿润锋运移距离随埋深的增大而减小,运移距离与入渗历时之间均符合对数函数关系,且竖直向下的运移距离均大于竖直向上;土壤含水率均随着土层深度的增加而先增加后减小,对于同一土层,灌水器处土壤含水率最大,其次为交汇面处,而距离灌水器12.5 cm处土壤含水率最小;土壤铵态氮和硝态氮均随土层深度的增加而先增加后减小,在水平方向,距离灌水器越近,铵态氮的质量浓度越大,对于硝态氮而言,灌水器埋深不同,硝态氮的分布存在明显差异。【结论】灌水器埋深对涌泉根灌双点源交汇入渗红壤的水氮运移分布均有显著影响,且埋深超过60 cm时,氮肥淋失风险较大,且对作物吸收不利。

【Background】The red soil widely distributed in hilly regions in southern China is an important soil resource,but the seasonal drought in these regions and the inherent acidity,stickiness and leanness of the red soil could impede crop growth.Surge-root irrigation(SRI)is a technology capable of ameliorating these problems and improving agricultural production in these regions.Understanding the movement of water and nitrogen in the soil under SRI is essential to improving its efficacy.【Objective】The purpose of this paper is to experimentally study the impact of burying depth of the dual-emitters in SRI on water and nitrogen movement in the red soil in attempts to provide a guidance for improving nitrogen utilization efficiency in these regions.【Method】The experiment was conducted in field with calcium ammonium nitrate as the nitrogen fertilizer;the emitters were buried at depth of 30,45,or 60 cm,respectively.For each treatment,we measured water infiltration from the emitters,movement of the wetting fronts,spatiotemporal changes in soil moisture,ammonium and nitrate,from which we derived formulae to calculate the changes in cumulative infiltration and location of the wetting front with time.【Result】When the emitter depth was30,45 and 60 cm,the cumulative infiltration and the stable infiltration rate were 18.84 L and 0.035 cm/min,17.09 L and 0.031 cm/minand 14.37 L and 0.024 cm/min,respectively,indicating thatthe deeper the emitters were,the less the cumulative infiltration and stable infiltration rate were.The cumulative infiltration increased with time in a power-law,and when the emittersdepth was 30,45 and 60 cm,the time it took the wetting fronts emanating from the two emitters to cross was 168,187 and 197 min,respectively.The migrating distance of the wetting front increased with the buried depth of the emitters,and it was related to irrigation time logarithmically.Vertically,soil moisture content(SWC),ammonium and nitrate all increased first and then decreased.Horizontally,both SWC and ammonium were the highest in the proximity of the emitters and the lowest at a location 12.5 cm from the emitters.In contrast,the nitrate distribution varied significantly with the burying depths of the emitters【Conclusion】The burying depth of the emittersin the SRIhad significant effects on water and nitrogen transport in red soils.Burying the emitters deeper than 60 cm could risk nitrogen leaching to groundwater and should be avoided.