(218) Optimum Soil K Application and Sufficient Leaf K concentration for Fresh Market Tomatoes Grown on a Midwest Fine Textured Soil

Abstract

Tomato transplants were set mid-May 1998, 1999, and 2001, with black plastic mulch and a single line source drip irrigation system. The soil type was a well-drained, central Iowa loam (prairie developed on glacial till) with 2.4% organic matter, 13.1 CEC, and a pH of 6.8. The soil test level of 89 kg·ha-1 of K was considered low for field corn and would require 121 kg·ha-1 of K for optimum yield. The experimental design was a factorial, split-plot, randomized complete block with four replications. The whole unit was K rates (0 to 372 kg·ha-1 of K as KCl). The subunit was cultivar, either `Mtn. Spring' (a determinate) or `Jet Star' (an indeterminate). Fruit harvest began the first week of August and continued weekly for 5 to 8 weeks. As expected, `Jet Star' produced from 12% to 35% more total fruit than `Mtn. Spring'. The K response was best described by a quadratic function. Total maximum yield occurred from 325 to 372 kg·ha-1 of K, depending on the production year. Cullage was high, mostly as a result of ripening disorders, and `Jet Star' consistently produced more culls than `Mtn. Spring', 10% to 11%. Increasing soil K rate did not reduce the percentage of culls. For 2001, increasing K rate to 300 kg·ha-1 of K enhanced `Mtn. Spring' marketable fruit size 18%, from 258 g to 305 g each, but not `Jet Star', which remained at 258 g. There was a difference (P< 0.01) between the varieties for leaf K; `Mtn. Spring' consistently had higher K concentrations, from 0.2% to 0.4%. The leaf K sufficiency range at the rapid flowering and vegetative growth stage was determined to be 3.10% to 3.25% with the corresponding petiole leaf sap K (using a dilution of 1 sap: 1 water) of 5000 mg·kg-1, for the same time period. The correlation between the Cardy meter petiole sap K values and whole leaf K was r= 0.83.