Smart farms and precision agriculture require automatic monitoring and supply of water and nutrients for crops, but sensors to monitor plant available nutrients in soil are not available. Soil electrical conductivity (EC) is related to nutrients in soil solution, which can be affected by soil organic matter, soil texture, temperature, and water content. Therefore, the objective of this study is to evaluate factors influencing soil EC sensor values by monitoring EC under different soil organic matter and water contents. Ten soil samples with various sand and clay contents, EC, pH, and organic matter contents were selected and saturated with water. Volumetric water content and EC of the soil were monitored while drying the soil. Humic acid and manure were added to soils in order to evaluate the effect of organic matter on soil EC. Soil EC values linearly increased with increasing water content at 10–25% which is favorable water content for plant growth. The EC increased when organic matter was added to soils, which was related to ions released from the organic matter. Soil EC calibration factor for soil water content increased when EC of the soil was high and organic matter was added. The sensor EC values in sandy loam and loam soils was related to the ion contents in pore water, and exchangeable ions in soil, respectively. Sensor EC values were highly correlated with organic matter and K contents in soil and can be used as an indicator for plant available nutrients in soil. Therefore, the sensor EC at optimal soil water content for plant growth can be used to monitor changes in plant available nutrients in soil.

中文翻译：

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监测土壤EC，预测不同土壤水分和有机质含量下的土壤养分状况

智能农场和精准农业需要自动监测和供应农作物的水和养分，但目前还没有监测土壤中植物有效养分的传感器。土壤电导率（EC）与土壤溶液中的养分有关，受土壤有机质、土壤质地、温度和含水量的影响。因此，本研究的目的是通过监测不同土壤有机质和水分含量下的EC，评估影响土壤EC传感器值的因素。选择十个具有不同沙子和粘土含量、EC、pH 和有机质含量的土壤样品并用水饱和。在干燥土壤的同时监测土壤的体积含水量和EC。将腐植酸和粪肥添加到土壤中，以评估有机质对土壤电导率的影响。土壤EC值随着含水量的增加而线性增加，在10-25%有利于植物生长的含水量。当土壤中添加有机物时，EC增加，这与有机物释放的离子有关。当土壤EC较高且添加有机质时，土壤含水量的土壤EC校准因子增加。沙壤土和壤土中的传感器EC值分别与孔隙水中的离子含量和土壤中的可交换离子含量有关。传感器EC值与土壤中有机质和钾含量高度相关，可以作为土壤中植物有效养分的指标。因此，传感器EC在植物生长的最佳土壤含水量下可用于监测土壤中植物有效养分的变化。