Irrigation well water in Nebraska: essential nutrient contents and other properties

Water nutrient concentrations and other properties were surveyed by sampling water from 642 irrigation wells in Nebraska. The amount of Ca, Mg, S, Cl, and B applied in irrigation exceeds removal in 15 Mg ha-1 of corn (Zea mays L.) grain harvest for most wells. Irrigation supply exceeded corn grain harvest removal of K, Mn and Mo for >20% of the wells. The supply of P, Zn, Cu, Fe, and Mo was generally very low but sufficient with some wells to be considered in nutrient management plans. The median level of nitrate N was 4.4 ppm with 25% of the wells having >10 ppm NO3-N which is above the suitability limit for human consumption. The agricultural lime equivalent applied with one or two ML of irrigation was enough to neutralize the acidifying effect of 200 kg ha-1 of fertilizer-N for 70% or 89% of the wells. Nutrient and lime supply was relatively low for Sandhills wells and relatively high for wells in river valleys of <100 ft depth. No wells had excessive Na levels but 0.3% of the wells had salinity levels of concern. A grouping of wells into 11 aquifer, geological formation and well-depth combinations accounted for >20% of the variation for most water properties but much variation occurred within groups. Sampling of the well water is needed for full optimization of nutrient and soil management. Information on nutrients supplied through irrigation should be complemented by regular soil testing and the use of recommended nutrient management guidelines.

Methods
Water of 642 irrigation wells was sampled and analyzed for 17 properties. Data was analyzed and presented by 11 well categories based on aquifer, geological formation and well depth.

本研究采集美国内布拉斯加州642眼灌溉井的水样，对其中的养分浓度及其他水质指标展开调查。对于绝大多数灌溉井，随灌溉水输入的钙（Ca）、镁（Mg）、硫（S）、氯（Cl）及硼（B）总量，超过了每公顷15 Mg的玉米（Zea mays L.）籽粒收获所带走的养分量。超20%的灌溉井中，随灌溉水输入的钾（K）、锰（Mn）及钼（Mo）总量，高于玉米籽粒收获所带走的对应养分量。磷（P）、锌（Zn）、铜（Cu）、铁（Fe）及钼（Mo）的灌溉输入量整体偏低，但部分灌溉井的输入量足以纳入养分管理计划的考量范畴。水样中硝态氮（nitrate N）的中位数浓度为4.4 ppm，其中25%的灌溉井其硝态氮浓度超过10 ppm（NO₃-N），该数值已超出人类饮用水的安全限值。1或2兆升（ML）灌溉水所携带的农用石灰当量，足以中和70%或89%的灌溉井中，每公顷200 kg氮肥所产生的酸化效应。内布拉斯加沙丘区（Sandhills）的灌溉井，其养分与石灰输入量整体偏低；而深度小于100英尺的河谷地带灌溉井，对应输入量则相对较高。所有灌溉井均未出现钠（Na）浓度超标的情况，但有0.3%的灌溉井存在需关注的盐度问题。将灌溉井按含水层、地质构造及井深组合划分为11个类别后，该分类方式可解释绝大多数水质指标20%以上的变异，但组内仍存在大量未被解释的变异。若要实现养分与土壤管理的全面优化，需对灌溉井水开展系统性采样分析。灌溉水输入的养分相关信息，需结合常规土壤测试及推荐的养分管理指南进行综合应用。

## 研究方法
本研究共采集642眼灌溉井的水样，对17项水质指标进行分析。后续数据分析与结果呈现均基于含水层、地质构造及井深划分的11个灌溉井类别展开。