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Catherine S. Fleming, Mark S. Reiter, Joshua H. Freeman and Rory Maguire

Determining irrigation requirements for fresh market tomato (Solanum lycopersicum) production is essential to obtain optimum yields, cost-effective water use, and minimize nitrate leaching. The objective of this study was to determine the appropriate irrigation rate for polyethylene-mulched fresh market tomato grown in Virginia. This study investigated irrigation regimes by applying water based on evapotranspiration (ET) calculations in three spring and three fall seasons. Plants were grown using 0.0 × ET, 0.5 × ET, 1.0 × ET, 1.5 × ET, and 2.0 × ET. Additional irrigation treatments involved tensiometers installed at 12-inch depth in the bed, programmed to irrigate at soil moisture set points of −20, −40, and −60 kPa. Tensiometer treatments were able to irrigate up to nine times per day if soil moisture fell below the designated moisture set point. Measurements included fruit yield, plant and fruit nitrogen (N) uptake, and inorganic soil nitrate-N (NO3-N) at 0 to 10-, 10 to 20-, and 20 to 30-inch depths. Overall, the 0.5 × ET treatment provided optimum yields in all growing seasons except Spring 2010, which was unseasonably hot and dry. A tensiometer treatment (−40 kPa) provided optimum yields in all growing seasons, and was able to adjust irrigation in a hot and dry season. Residual soil NO3-N at 0 to 10 inches generally exhibited an inverse relationship with yield; greater yields resulted in less residual soil NO3-N. In most treatments throughout the duration of this study, plant N uptake + fruit N uptake accounted for most of the N fertilizer applied (68% to 151%). In conclusion, an irrigation rate of 0.5 × ET and a tensiometer treatment (−40 kPa) provided minimal irrigation inputs to obtain optimum marketable yields while also minimizing residual soil nitrate that may be prone to leaching after the season.