Abstract. Adding mineral fertilizers and mineral nutrient is a common practice in conventional farming and fundamental to maintain optimal yield and crop quality, whereby nitrogen is the most applied fertilizer often used excessively, leading to adverse environmental impacts. To assist farmers in optimal fertilization and crop management, non-invasive geophysical methods can provide knowledge about the spatial and temporal distributions of nutrients in the soil. In recent years, electromagnetic induction (EMI) is widely used for field characterization, to delineate soil units and management zones or to estimate soil properties and states. Additionally, ground penetrating radar (GPR) and electrical resistivity tomography (ERT) have been used in local studies to measure changes of soil properties. Unfortunately, the measured geophysical signals are confounded by horizontal and vertical changes of soil states and parameters and the single contributions of those states and parameters are not easy to disentangle. Within fields, and also between fields, fertilization management might vary in space and time, and therefore, the differences in pore fluid conductivity caused directly by fertilization, or indirectly by different crop performance, makes the interpretation of large-scale geophysical survey over field borders complicated. To study the direct effect of mineral fertilization and its effects on the soil electrical conductivity, a field experiment was performed on 21 bare soil plots with seven different fertilization treatments. As fertilizers, calcium ammonium nitrate (CAN) and potassium chloride (KCl) were chosen and applied in three dosages. Soil water content, soil temperature, and bulk electrical conductivity were recorded permanently over 450 days. Additionally, 20 EMI, 7 GPR, and 9 ERT surveys were performed and at days of ERT measurements soil samples for nitrate and reference soil electrical conductivity measurements were taken. The results showed that the commonly used CAN application dosage did not impact the geophysical signals significantly. On the other hand, EMI and ERT were able to trace back the temporal changes in nitrate concentrations in the soil profile over more than one year. On the other hand, the results also showed, that both techniques were not able to trace the nitrate concentrations in the very shallow soil layer of 0–10 cm. Irrespectively of the low impact of fertilization on the geophysical signal, the results indicated that past fertilization practices cannot be neglected in EMI studies, especially if surveys are performed over large areas with different fertilization practices or crop grown with different fertilizer demands or uptake.

中文翻译：

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使用延时电磁感应评估土壤施肥效果


摘要。添加矿物肥料和矿物营养剂是传统农业的常见做法，是保持最佳产量和作物质量的基础，其中氮肥是施用最多的肥料，经常被过度使用，导致不利的环境影响。为了帮助农民进行最佳施肥和作物管理，非侵入性地球物理方法可以提供有关土壤中养分空间和时间分布的信息。近年来，电磁感应 （EMI） 被广泛用于田间表征、划定土壤单元和管理区或估计土壤特性和状态。此外，探地雷达 （GPR） 和电阻率断层扫描 （ERT） 已用于当地研究以测量土壤特性的变化。不幸的是，测得的地球物理信号受到土壤状态和参数的水平和垂直变化的混淆，并且这些状态和参数的单一贡献不容易解开。在田地内部以及田地之间，施肥管理可能在空间和时间上有所不同，因此，由施肥直接或间接由不同的作物性能引起的孔隙流体电导率差异，使得对田间边界的大规模地球物理调查的解释变得复杂。为了研究矿物施肥的直接影响及其对土壤电导率的影响，在 21 个裸土地块上进行了 7 种不同的施肥处理的田间试验。作为肥料，选择硝酸铵钙 （CAN） 和氯化钾 （KCl） 并分三种剂量施用。土壤含水量、土壤温度和体电导率在 450 天内被永久记录。 此外，还进行了 20 次 EMI、7 次 GPR 和 9 次 ERT 调查，并在 ERT 测量的几天内采集了用于硝酸盐和参考土壤电导率测量的土壤样本。结果表明，常用的 CAN 应用剂量对地球物理信号没有显著影响。另一方面，EMI 和 ERT 能够追溯土壤剖面中硝酸盐浓度在一年多的时间变化。另一方面，结果还表明，这两种技术都无法追踪 0-10 厘米的极浅土壤层中的硝酸盐浓度。尽管施肥对地球物理信号的影响很小，但结果表明，在 EMI 研究中不能忽视过去的施肥做法，特别是如果以不同的施肥做法在大面积区域进行调查，或者以不同的肥料需求或吸收方式种植的作物。