Soil quality changes due to flood irrigation in agricultural fields along the Rio Grande in western Texas
Soil quality changes due to flood irrigation in agricultural fields along the Rio Grande in western Texas
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DOI：
10.1016/j.apgeochem.2017.12.019
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发表时间：
2018-03-01
影响因子：
3.4
通讯作者：
Ma, Lin
中科院分区：
文献类型：
--
作者：
Cox, Christine;Jin, Lixin;Ma, Lin
不断增长的人口需要更多的食物，给世界各地的土壤生产力和可持续性带来更大的压力。在得克萨斯州西部沿着格兰德河流域，自然降雨量低，需要频繁灌溉以维持农业。为了调查灌溉对土壤质量的影响，我们收集了地球化学数据并进行了建模（主要元素和养分）对灌溉水，土壤孔隙水，排水和土壤样品，并监测土壤水分，温度和电导率与传感器从两个山核桃，一个棉花，在德克萨斯州西部的一个苜蓿地。这项研究表明，（格兰德河）和地下沃茨显着增加根区盐度，土壤碱度和养分淋溶从土壤到底层含水层和格兰德河从干旱的西南农业领域。灌溉用水中总溶解性固体含量较高（一般> 500 ppm），以Na+、Cl-、Ca 2+和SO 42-为主。在洪水灌溉后，渗透水溶解了由于先前的灌溉而在土壤中积累的盐，例如石膏，或/和混合了现有的浓缩土壤沃茨，并且相对于这些蒸发岩矿物接近饱和。土壤水相对于碳酸盐过饱和，因为成土方解石沉淀出来，并达到类似于总土壤质量的10重量%的浓度。这表明，成壤碳酸盐是一个重要的碳库和沉淀动力学和控制等次生方解石需要进一步调查灌溉农田在干旱地区的世界。农业回流样品的化学从排水沟收集的灌溉水是相似的，这表明，大部分的灌溉水采取了浅，短的流道通过田间排水沟。在灌溉事件之间，土壤水分变得更加集中，因为水分通过蒸发蒸腾作用损失，导致蒸发盐沉淀。因此，土壤，特别是粘性土壤的碱度和含盐量经常超过该区域种植的主要作物的耐受水平。在这些质地良好的土壤中，高蒸散率、高盐度水的密集灌溉和有限的入渗相结合，阻碍了作物生长，降低了土壤孔隙度和渗透性，导致通气性差，并通过正反馈机制加速了盐分积累。在土壤饱和的初始灌溉期间，土壤水分也被蒸发并重新充入下层含水层，因此盐分、养分、以及来自农业实践的痕量金属（即，施肥、灌溉、土壤改良剂和杀虫剂）可以调动到浅层地下水。这意味着格兰德河、地下水和土壤的化学性质密切相关。因此，农业的可持续性取决于适当的水、土壤和作物管理做法。
Growing populations demand more food, putting more pressure on soil productivity and sustainability around the world. In western Texas along the Rio Grande Valley, the low natural rainfall requires frequent irrigations for sustaining agriculture. To investigate the impacts of irrigation on soil quality, we collected and modelled geochemical data (major elements and nutrients) on irrigation water, soil pore water, drainage water, and soil samples, and monitored soil moisture, temperature, and electrical conductivity with sensors from two pecan, one cotton, and one alfalfa fields in western Texas.This study showed that flood irrigation with both surface (Rio Grande river) and ground waters significantly increased the root-zone salinity, soil sodicity, and nutrient leaching from soils to the underlying aquifers and Rio Grande river from agricultural fields of the arid southwest. The water used for irrigation was high in total dissolved solids (> 500 ppm generally), dominated by Na+, Cl-, Ca2+ and SO42-. After flood irrigation, infiltrating water dissolved salts such as gypsum that have accumulated in the soils due to previous irrigations, or/and mixed existing concentrated soil waters, and approached saturation with respect to these evaporite minerals. Soil water was supersaturated with respect to carbonates as pedogenic calcite precipitated out and reached concentrations of similar to 10 wt% of total soil mass. This suggested that pedogenic carbonate is an important carbon reservoir and precipitation kinetics and controls of such secondary calcite need further investigation for the irrigated agricultural fields in arid regions of the world.Chemistry of agricultural return flow samples collected from drainage ditches was similar to that of irrigation water, suggesting that most of the irrigation water had taken a shallow and short flowpath through the fields to drains. Between irrigation events, soil water became more concentrated as water was lost through evapo-transpiration that led to precipitation of evaporite salts. As a result, sodicity and salinity of soils, especially clayey soils, frequently exceeded the tolerance levels of major crops grown in the region. Here in these fine-textured soils, combination of high evapotranspiration rates, intensive irrigation with water of elevated salinity, and limited infiltration stunted crop growth, decreased soil porosity and permeability, led to poor aeration, and accelerated salt buildup via a positive feedback mechanism.During initial irrigation where soils were saturated, soil water also percolated and recharged to underlying aquifers, and thus salts, nutrients, and trace metals from agricultural practices (i.e., application of fertilizers, irrigation, soil amendments, and pesticide) could be mobilized to shallow groundwaters. This implied that chemistry of Rio Grande river, groundwater, and soil was closely linked. Thus the sustainability of agriculture depended on appropriate water, soil and crop management practices.