Movement of the Wetted Front under Drip-irrigated Tomatoes Grown on a Sandy Soil

摘要

Keeping water and nutrients within the rootzone of vegetable crops is the main goal of nutrient Best Management Practices. Because the actual depth of water movement below a crop depends on the volume of water applied and how much water is taken up bythe plant, it is possible that reducing drip irrigation system operating pressure (OP) as a means to increase the length of irrigation time may result in slower vertical water movement due to 1) greater lateral water movement and 2) increased plant water uptake. Without a crop, water moved in a deep sandy soil at rate of 0.057 to 0.17 mm/L/100 m (0.3 to 0.9 inch/10 gal/100 ft). Assuming a typical daily irrigation schedule of 2 h using a flow rate of 300 L/100 m/h (24 gal/100 ft/h), the estimated wettedsoil depth would be 216 to 650 cm (86 to 260 inches) after 60 d In this study tomato plants were grown for two seasons using plasticulture. Treatments were OP of 41 and 82 kPa (6 and 12 psi) and two irrigation rates of 100% and 75% of the UF-IFAS recommended rate. Blue dye was injected on 14 and 21 DAT and the soil was dug on 80 and 84 DAT in 2008 and 2009, respectively. The depth of waterfront was significantly affected by OP (P = 0.01) with maximum average wetted depths of 130 and 158 cm (52 and 63 inches) at 42 kPa (6 psi) and 160 and 168 cm (64 and 67 inches) at 84 kPa (12 psi), respectively, for 2008 and 2009. Surprisingly, irrigation rate effect was not significant on the depth of waterfront at 145 and 165 cm (58 and 66 inches) at 100% IRR and 143 and 163 cm (57 and 65 inches) at 75% IRR in 2008 and 2009, respectively. While reducing OP significantly reduced the downwards movement of water in the soil, it was not sufficient to keep the irrigated water from moving beyond the crop rootzone on a sandy soil. Hence, reduced OP should not be relied upon as a panacea, but should be used together with other nutrient BMPs.