LOW-‎COST SOIL ‎MOISTURE SENSORS’ ASSESSMENT FOR THEIR ACCURACY AFTER CALIBRATION THROUGH THE ‎GRAVIMETRIC METHOD

Abstract

The existing study aimed to assess ‎four soil moisture sensors’ capacitive (WH51 and SKU: ‎SEN0193) and ‎resistive (Yl69 and IC Station) abilities, which are affordable and medium-priced for their accuracy in six common soil types in the central region of Iraq. The readings’ calibration for the soil moisture sensor devices continued through two gravimetric methods. The first depended on the protocols’ database, while the second was the traditional calibration method. The second method recorded ‎the ‎lowest analysis error ‎compared with the first. The ‎moderate-cost sensor WH51 showed the lowest standard error (SE), MAD‎, and RMSE and ‎the highest R² in ‎both methods. The performance accuracy of ‎WH51 was close to ‎readings shown ‎by the manufacturing company (1%), as the MAD ‎amounted to 1.62%. Through both methods, the ‎average MAD for ‎sensors ranged ‎from 4.76% to 7.36%, with ‎this result ‎considered acceptable, especially for low-cost ‎sensors with insufficient available information for accuracy. In ‎general, the average mean absolute percentage (MAPE) for ‎all sensors was 25.54%, which ‎means that the validity ‎of the measurement for the ‎low-cost sensors reached ‎75%. It ‎encourages their use by plant breeders in ‎irrigation, as the error rate was less ‎than the ‎specified depletion of 50% for available water in ‎irrigation, where all study textures showed that the sensor reading reached the limits of 72 (±2), adopting 3% MAD for all sensors. The study affirms that, except for the IC station ‎sensor recommended for irrigation use only in sandy-sandy loam soils, low-cost sensors have suitable accuracy for irrigation management.