Many microbes, including several fungal plant pathogens, often reside at or very near the soil surface. Survival, reproduction, and development of these pathogens are influenced by moisture in the environment. There are currently no efficient means to continuously monitor wetness conditions at the soil-air interface. A project was initiated to develop a sensor for continuous monitoring of soil-surface wetness and to be used in conjunction with data-logging equipment. Sensors were developed and tested for consistency and durability through replicate trials conducted on synthetic sponges and on thin soil layers. Field trials were then conducted to test sensor durability and response to field environments. Under greenhouse conditions, sensors were calibrated against tactile estimates of wetness on thin layers of three soil textures (sandy loam, clay loam, and silt loam) over a range of known moisture levels. In laboratory tests, sensors were evaluated for uniformity of response. Sensors were shown to be uniform in response under laboratory and field conditions. They worked well to indicate wetting events in the field and allowed for determination of wetness duration, a parameter of great interest to plant pathologists. The sensors, in conjunction with automatic data-logging devices, may be able to provide estimates of wetness duration for incorporation into disease predictive models.
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