Influence of soil conditioners for enhanced water retention on the accuracy and longer‐term deployment of widely used soil moisture sensors

Abstract In precision agriculture, water content sensors are fundamental to monitor soil moisture and hence optimize irrigation scheduling. Climate‐smart agriculture has also focused on improving soil moisture retention by using soil conditioners. However, despite that ‘sensor deployment’ and ‘soil conditioners’ are both intended to improve water use efficiency, data are lacking on the responses of soil water sensors to soil conditioners for enhanced water holding capacity. We evaluated soil moisture sensor readings taken in a sandy loam soil, with added biochar (2.5% w/w), compost (5% w/w), hydrogel (0.6% w/w) and water treatment residues (WTR; 5% w/w). The soils were saturated and then subjected to wetting and drying cycles. Measurements were taken continuously using multiple commercial sensors: ML3 and SM150T soil moisture sensors (Delta‐T Devices) as well as EC‐5 soil moisture sensors (Meter). The accuracy of the tested sensors was reduced by the addition of conditioners in the following order: biochar <WTR<compost <hydrogel. Sensor accuracy was highly dependent on soil water content, with larger deviations from actual values when soil water content <0.14 m 3 m −3 . All sensors performed best at mid values of soil water content (0.14–0.33 m 3 m −3 ), where ML3, SM150T and EC‐5 sensor readings did not differ significantly from the actual water content in unamended soil. The presence of conditioners did affect such accuracy, but the application of a soil + conditioner − specific calibration was effective in increasing sensor accuracy in this water content range.