The 2010 ASHS Annual Conference

Increasing the length of irrigation time by reducing the operating pressure of drip irrigation systems may result in reduced deep percolation and may allow for reduced N fertilizer application rates, thereby reducing the environmental impact of tomato production.  The objectives of this study were to determine the effects of reduced drip-irrigation operating pressure (OP, 84 and 42 kPa), N fertilizer rate (100%, 80% and 60% of the recommended 224 kg N/ha rate), and irrigation rates (100% and 75% of the recommended 9,340 L/ha/day/string rate), on fresh market tomato nutritional status and yield. Nitrate-nitrogen concentration in petiole sap of ’Florida 47’ tomatoes grown in the spring of 2008 and 2009 in a raised bed plasticulture system were not affected by treatments in both years and were within the sufficiency ranges at first flower, two-inch fruit and first-harvest growth stages (420-1150, 450-770 and 260-450 mg/L, respectively). Total marketable yields were significantly higher at 42 than at 84 kPa OP (21 vs 17 t/ha respectively; p<0.01) in 2008, but were significantly higher at the 84 kPa OP (48 t/ha vs 44 t/ha at 42 kPa, p=0.05) and 100% nitrogen rate (49 t/ha vs 44 t/ha at 50% and 75% N rate, p=0.04) in 2009. Irrigation rate did not have any significant effect on tomato marketable yields in either years with no interaction between irrigation rate and N or OP treatments. Hence, growing tomatoes at 84 kPa OP, 100% of recommended N rate and 75% of recommended irrigation rate provided the highest marketable yields with least inputs in a drip irrigated plasticulture system.  These results suggest that smaller amounts of irrigation water and fertilizers (50% and 75%, respectively, of recommended N and irrigation rates) could be applied when using a low irrigation operating pressure of 42 kPa for the early part of the tomato crop season. In the later part, as water demands increased, the standard operating pressure of 84 kPa could be used. Changing the irrigation operating pressure offers the grower some flexibility to alter the flow rates to suit the water demands of various growth stages of the crop. Furthermore, it allows irrigation to be applied over an extended length of time which could better match plants’ needs for water throughout the day. Such an irrigation strategy could improve water and nutrient use efficiencies and reduce the risks of nutrient leaching.