Irrigation consumes the largest share of freshwater resources, but is a necessary practice to boost agricultural output to meet increasing global demand for food and fiber. Irrigation not only impacts water quantity but can also degrade water quality. Research efforts have explored various aspects of irrigation efficiency and irrigated crop productivity, but few studies have examined how different crops collectively modulate water utilization and water quality at the watershed scale. The objective of this study was to determine how the fractions of evapotranspiration (fET) water ascribed to major crops impact water quantity and quality in irrigation return flow. In this study, long-term water quantity and quality monitoring data, collected as part of the Conservation Effects Assessment Project (CEAP), combined with crop and evapotranspiration (ET) modeling products, were used to build relationships between water quantity and quality metrics and fET associated with major crops during the first 15 years of the CEAP Twin Falls irrigation project. Results suggest that subwatershed size and subsurface flow contribution in regional drainage tunnels influenced the observed hydrologic patterns and led to two distinct groups. Subwatersheds in group 1 were large, typically included subsurface drain tunnels, and had high return flow volumes and low sediment concentration, while those in group 2 were smaller in size, had low return flow volumes, and high sediment concentration. Multiple linear regression analyses showed that spring and summer irrigation return flow volumes normalized by subwatershed area increased as a function of fET of potato ( Solanum tuberosum ) in group 1 (regression coefficients [coef.] = 4.42 in spring and 1.54 in summer) but were inversely associated with small grains in the fall (coef. = −1.67 and −0.60 in groups 1 and 2). Spring sediment concentration had negative regression coefficients with fET of sugar beet ( Beta vulgaris ) (coef. = −911.00) and alfalfa ( Medicago sativa ) + pasture crops (coef. = −424.85) in group 2. When statistically significant, a negative association was found between phosphorus (P) load per return flow volume and fET of alfalfa + pasture (coef. = −0.68 to −1.07), corn ( Zea mays ) (coef. = −0.64 to −0.89), dry beans ( Phaseolus vulgaris ) (coef. = −1.25 to −1.87), and sugar beet (coef. = −1.54 to −2.83) across aggregation periods and subwatershed groups. Nitrate (NO3-N) load per return flow volume was negatively associated with potato and corn fET in group 1 especially during the spring (coef. = −31.13 for potato and −9.60 for corn) and fall (coef. = −14.54 for potato and −4.43 for corn) months but positively associated with dry beans (coef. = 4.87) over the irrigation season. While direct cause and effect were not established with this analysis, results from this study provide valuable information about various crop production systems that may impact observed hydrologic responses.

中文翻译：

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灌溉流域主要作物生产与水质之间的模式和关联

灌溉消耗了最大比例的淡水资源，但却是提高农业产量以满足全球对粮食和纤维日益增长的需求的必要做法。灌溉不仅会影响水量，还会降低水质。研究工作探索了灌溉效率和灌溉作物生产力的各个方面，但很少有研究探讨不同作物如何在流域范围内共同调节水利用和水质。本研究的目的是确定主要作物的蒸散量 (fET) 水的比例如何影响灌溉回流中的水量和质量。在本研究中，作为保护效果评估项目 (CEAP) 一部分收集的长期水量和质量监测数据，结合作物和蒸散量 (ET) 建模产品，用于建立水量和质量指标之间的关系，以及在 CEAP 双子瀑布灌溉项目的前 15 年中，fET 与主要作物相关。结果表明，区域排水隧道中的次流域大小和地下流量贡献影响了观察到的水文模式，并导致了两个不同的群体。第 1 组的子流域较大，通常包括地下排水隧道，回流量高，含沙量低；而第 2 组的次流域面积较小，回流量低，含沙量高。多元线性回归分析表明，根据第 1 组马铃薯 (Solanum tuberosum) 的 fET 函数，按次流域面积归一化的春季和夏季灌溉回流量有所增加（春季回归系数 [coef.] = 4.42，夏季回归系数 [coef.] = 1.54），但与秋季的小颗粒呈负相关（第 1 组和第 2 组中的系数 = -1.67 和 -0.60）。春季沉积物浓度与第二组中甜菜 ( Beta vulgaris ) (coef. = -911.00) 和苜蓿 (Medicago sativa ) + 牧草作物 (coef. = -424.85) 的 fET 具有负回归系数。当统计显着时，负相关发现紫花苜蓿+牧草（系数 = -0.68 至 -1.07）、玉米（玉米）（系数 = -0.64 至 -0.89）、干豆（菜豆）的单位回流体积磷 (P) 负荷与 fET 之间）（系数 = -1.25 至 -1.87），以及甜菜（系数 = -1.54 至 -2.83）跨越聚集期和亚流域群体。每回流体积的硝酸盐 (NO3-N) 负荷与第 1 组中的马铃薯和玉米 fET 呈负相关，特别是在春季（马铃薯 coef. = -31.13，玉米 -9.60）和秋季（马铃薯 coef. = -14.54）玉米为-4.43）个月，但与灌溉季节的干豆（coef.= 4.87）呈正相关。虽然本分析未确定直接因果关系，但本研究的结果提供了有关可能影响观察到的水文响应的各种作物生产系统的宝贵信息。