Measurement of soil moisture content is very important for efficient crop production and irrigation scheduling. A prototype soil moisture sensor was made that would, in theory, accurately measure water available to plants. In principle our soil moisture sensor determines the soil moisture content through deficit in water vapor pressure from saturation. Our sensor gave a significant response (0.59 kPa) to ambient air present in the silicone tubing at the start of the experiment, suggesting that it was sensitive to relatively dry air. However, subsequent measurements varied periodically between 0.1 kPa to -0.15 kPa, over a large range in soil moisture content (36 % v/v to 0.24 % v/v). The regular periodic response suggests that the experimental setup and/or protocol require modifications. Also since the soil was saturated with water at the start of the experiment, water might have entered the tubing, affecting the sensor performance. Thus, in future trials care must be taken to exclude liquid water from the sensor.