Abstract
A low-volume/high frequency (LVHF) soil moisture based drip irrigation system was tested on a commercial tomato farm in south Florida. Seven irrigation treatments were compared. In the first six treatments, the system was pressurized by means of an electrical pump and a pressure tank, and controlled by an irrigation timer (controller) set to irrigate five times per day. The last treatment consisted of the farm's standard commercial practice where a portable pump was used on a twice weekly manual irrigation schedule. Four of the six LVHF treatments resulted from interfacing in a closed control loop with the irrigation controller two types of soil moisture sensors (switching tensiometers and granular matrix sensors) set at two moisture points (wet: 10 cbar, optimal:15 cbar), i.e., irrigation was allowed to start when the soil moisture measured by the sensor was below the set point. The other two LVHF resulted from the same system with no sensors set with the timer at two irrigation schedules, one to supply 100% of the maximum recommended seasonal crop water needs (12 min per irrigation) and the other to supply 150% of those needs (18 min per irrigation). Results from the six LVHF treatments show that tomato yields were not different from that of the commercial field while conserving water. Switching tensiometers at 15 cbar set point performed the best (up to 73% reduction in water use compared with commercial farm practice, and 50% with respect to the 100% recommended crop water needs treatment). Routine maintenance (refilling and pumping) was critical for reliable operation of the switching tensiometers, especially on the driest treatment of 15 cbar where twice weekly routine maintenance is recommended. Granular matrix sensors behaved erratically and did not improve water savings compared with the 100% recommended crop water needs treatment.
