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An automated soil moisture based drip irrigation system has been developed and tested on a tomato crop. The system employs a quantified irrigation controller (QIC) developed by the University of Florida to interface soil moisture monitoring devices with an irrigation timer. Prescheduled low volume high frequency events are either allowed or blocked if in-field soil moisture status is below or above a set threshold set point respectively.

The field experiment was conducted during the winter season of 2004/2005 in Miami-Dade County. Soil moisture based irrigation treatments used capacitance soil moisture probes and tensiometers, and time-based schedules used historical evapotraspiration and local farmer practices. Fertilizer was applied by fertigation and automatically injected using venturi injectors. Drainage lysimeters were used to collect leachate from the root zone to quantify differences in nutrient leaching. Large savings in applied water occurred for the soil moisture based treatments, without a reduction in total marketable yield compared to the time-based treatments (up to 80%). The soil moisture based treatments resulted in 30% reductions in both volume of leachate and phosphorous load leached for the season, when compared to grower practices. No significant differences were found for the load of nitrogen leached due to high variability within treatments. The soil moisture based system provides a viable means to increase water use efficiency, and reduce nutrient leaching from the root zone, which reduces operation costs and the potential for groundwater contamination. Further testing is suggested to determine the reduction in nitrogen leaching.