LEAF NUTRIENT CONTENT AND TOMATO FRUIT YIELD AS AFFECTED BY SINGLE SUPER PHOSPHATE RATES APPLIED BY DRIP IRRIGATION

A drip fertigation system should use low-cost phosphorus fertilizer available in small markets to smallholders such as especially Brazilian tomato growers. A study was conducted in an unheated greenhouse to establish an optimum rate of single superphosphate (SS) to formulate an aqueous solution that can be applied to tomato plants through a low-pressure drip irrigation system. Five rates of SS 18% phosphorus pentoxide (P₂O₅)] 0, 25, 50, 100, and 200 g·plant^?1, were evaluated in a randomized block design with four replications. Each rate was subdivided into 15 equal parts. Each part was dissolved in water (210 mL for each plant) and the mixture left to settle for 24 hours. The supernatant was applied by drip irrigation every week for 15 weeks. The tomato plants were grown in 9 dm³ plastic bags containing fertilized substrate in an unheated greenhouse. The leaf contents of nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), copper (Cu), and zinc (Zn) were not affected by the treatments. The highest phosphorus (P), manganese (Mn), and iron (Fe) leaf contents were obtained from plants fertilized with SS at 79; 0; 0 g·plant^?1, respectively. The marketable tomato fruit yield, measured up to 123 days after transplanting, increased with the increasing SS up to 54 g·plant^?1, resulting in a yield of 6.16 kg·plant^?1, corresponding to 10.3 kg·m^?2. A settled aqueous solution of SS (54 g·210 mL^?1 of water) can be applied weekly to tomato plant through a low-pressure drip irrigation system during the plant cycle.