Potassium requirements for maximum yield and fruit quality of processing tomato

A survey of 140 processing tomato (Lycopersicon esculentum Mill.) fields in central California was conducted in 1996-97 to examine the relationship be tween K nutrition and fruit quality for processing. Quality parameters eval uated were soluble solids (SS), pH, color of a blended juice sample, and th e percent of fruit affected by the color disorders yellow shoulder (YS) or internal white tissue (IWT), Juice color and pH were not correlated with so il K availability or plant K status, SS was correlated with both soil excha ngeable K and midseason leaf K concentration (r = 0.25 and 0.28,p < 0.01) b ut the regression relationships suggested that the impact of soil or plant K status on fruit SS was minor, YS and IWT incidence, which varied among fi elds from 0% to 68% of fruit affected, was negatively correlated with K sta tus of both soil and plant, Soil exchangeable K/root<(Mg)over bar> ratio wa s the measure of soil K availability most closely correlated with percent t otal color disorders (YS + IWT, r = -0.45,p < 0.01). In field trials conduc ted to document the relationship between soil K availability and the fruit color disorders, soil application of either K or gypsum (CaSO4, to increase K/root<(Mg)over bar> ratio) reduced YS and total color disorders, Multiple foliar K applications were effective in reducing fruit color disorders at only one of two sites. In no field trial did K application improve yield, S S, or juice color.