The Effects of Irrigation Water Turbidity and Soil Texture on Measurement Accuracy of Soil Water Content by TDR

This study was aimed to investigate the effect of irrigation water turbidity and soil texture on the measurement accuracy of soil water content using time domain reflectometry (TDR) device. Treatments consisted of three soil textures (silty clay, sandy loam, and clay loam) and three levels of irrigation water turbidity (0, 1500, and 3000 NTU). Volumetric soil moisture content (θv) was measured using a TDR device and compared with the gravimetric method measurements. Results showed that TDR has the highest accuracy in the sandy loam soil under different levels of water turbidity and by increasing the clay content, the accuracy of the device is reduced as confirmed by root mean square error (RMSE) values of 0.024, 0.027, and 0.038 in 0, 1500, and 3000 NTU turbidity, respectively, in this texture. Drawing of the coherence chart between the results obtained from TDR method and the gravimetric one showed that the highest and the least correlations between the two methods were observed in clay loam + well water treatment (R2 = 0.94) and silty clay + 1500 NTU (R2 = 0.84), respectively. Thus, increasing turbidity decreased the accuracy of the TDR device in all of the studied soil textures. Results also showed that the highest accuracy of TDR device was obtained in sandy loam + control treatment (0.0 NTU) conditions.