Effects of Preplant Potassium Sources and Rates for Tomato Production

Abstract

A two-season study was conducted to assess the effects of preplant potassium (K) fertilization rates and sources on the growth and yield of beefsteak tomato (Solanum lycopersicum). Fourteen treatments resulted from the combination of two K sources: sulfate of potash [SOP (0N–0P–42K)] and muriate of potash [MOP (potassium chloride, 0N–0P–50K)] and seven preplant K rates (0, 50, 100, 200, 300, 400, and 500 lb/acre). Soil electrical conductivity (EC) at 4 weeks after transplanting was influenced by the interaction between preplant K rates and sources. When SOP was applied, soil EC increased from 0.4 dS·m−1 with no preplant K application to ≈1.3 dS·m−1 with a rate of 500 lb/acre of preplant K. However, the soil EC steadily increased from 0.4 to 3.0 dS·m−1 as preplant K rates increased from 0 to 500 lb/acre when MOP was used as the nutrient source. The combined effect of the preplant application of K rates and sources influenced the seasonal extra-large and total marketable fruit weight, which increased steadily with K rates, regardless of the sources, from 0 to 300 lb/acre. At K rates between 300 and 500 lb/acre, there were no extra-large and total fruit weight differences among rates when SOP was applied. In contrast, extra-large and total marketable fruit weight declined when rates increased from 300 to 500 lb/acre of K and MOP was applied to the soil. Data demonstrated that plots treated with MOP at rates higher than 300 lb/acre of K increased soil EC and caused a decline on extra-large and total marketable fruit weight of tomato.