Excessive use of N fertilizers in agriculture often leads to NO₃⁻ accumulation in the unsaturated zone and to groundwater pollution. There is uncertainty regarding the variability in fertilizer transport and uptake efficiency due to the lack of studies based on continuous nondestructive measurements in unsaturated soils. In this study, we analyzed solute dynamics across the unsaturated zone underlying cultivated agricultural fields. Commercial crop rotations under four treatments, comprising two N fertilization regimes and two irrigation water salinity levels, were conducted in loess soil in the semiarid climate of the northern Negev Desert, Israel. The impact of the various treatments on water and solute dynamics below the root zone was monitored by a vadose zone monitoring system. The patterns of variations in soil water content and solute concentrations were analyzed using nonnegative tensor factorization. We found that irrigating using higher salinity water resulted in the earlier arrival of wetting fronts to the deeper layers and increased NO₃⁻ concentrations relative to the lower salinity treatments. Surprisingly, this effect was only seen in the deeper soil levels, whereas there was no significant difference in the arrival times and concentrations in the upper soil layers. Possible mechanisms are suggested and discussed.

中文翻译：

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灌溉水盐度的增加促进了硝酸盐向深层非饱和土壤的迁移

在农业中过量使用氮肥往往导致NO ₃ ^-堆积在非饱和带并受到地下水污染。由于缺乏基于非饱和土壤中连续非破坏性测量的研究，因此肥料运输和吸收效率的变化存在不确定性。在这项研究中，我们分析了耕作农田下面非饱和带的溶质动力学。在以色列北部内盖夫沙漠的半干旱气候下，在黄土土壤中进行了包括两种氮肥制度和两种灌溉水盐度水平在内的四种处理下的商业作物轮作。渗流区监测系统监测了各种处理对根区以下水和溶质动力学的影响。使用非负张量因子分解分析了土壤含水量和溶质浓度的变化模式。₃ ^-的浓度相对于下部盐度治疗。出乎意料的是，这种影响仅在较深的土壤中可见，而到达时间和上层土壤中的浓度没有显着差异。建议并讨论了可能的机制。