Optimizing Field Grown Tomato Yield: Effects of Grafting, Irrigation and Nitrogen Inputs

Grafting technology has evolved into a unique component of sustainable production of cucurbits and solanaceous vegetables in many countries outside of the U.S., particularly under intensive cultivation. In addition to managing soil-borne diseases, grafting with vigorous interspecific rootstocks is suggested to improve yield in tomato (Solanum lycopersicum) production due in part to enhanced nutrient and water uptake. However, the response of grafted tomato plants to different nitrogen and water supplies has not been fully examined in comparison with non-grafted plants, especially under field conditions. An experiment was conducted during the growing season of spring 2010 to determine the yield response of grafted tomatoes to different combinations of irrigation regimes and nitrogen fertilization rates, and to develop the nitrogen fertilization program for grafted tomato production in sandy soils in Florida. A popular tomato cultivar Florida-47 was grafted onto two selected interspecific rootstocks including ‘Beaufort’ and ‘Multifort’. Non-grafted ‘Florida-47’ was used as control. Plants were grown in twelve combinations of two irrigation regimes (Low and High) and six nitrogen rates (56, 75, 148, 224, 298, and 372 kg ha^-1) using a split-plot experimental design with 4 replications. The field was fumigated to eliminate interference of pest factors. The main effects of irrigation regimes and N rates were significant but no interaction effect was observed on total and marketable yields. Interestingly, high irrigation regime resulted in significantly lower yields than the low regime. At each nitrogen application level, significant difference between grafted vs. non-grafted plants was detected whereas the two rootstocks did not show differential response. The total and marketable yields were increased by 27 and 31% using grafted plants compared with the non-grafted control, respectively. Within each irrigation regime, it appeared that compared to other models tested the exponential model provided a better prediction of the marketable yields of grafted and non-grafted plants as a function of the nitrogen rates. Based on this exponential model and with 99.9% of the asymptotic maximum attainable marketable yield, the optimum N fertilization rates to reach optimum marketable yields were estimated as 258 and 153 kg ha^-1 for the grafted and non-grafted plants respectively, despite the irrigation regimes. The results indicated that higher than currently recommended nitrogen rate might be required for grafted ‘Florida 47’ tomato with vigorous interspecific rootstocks to optimize the marketable yield.