Effects of Varying Potassium Levels on Yields and Petiole Potassium Levels for Organically Fertilized High Tunnel Tomato

High tunnels provide a longer growing season and warmer overall temperatures than field sites. As a result, crops grown in high tunnels often exhibit increased biomass production, nutrient uptake, and yields. We therefore hypothesized that macronutrient uptake by high tunnel tomato crops may exceed levels previously determined for field-grown tomato crops. The objective of this research was to investigate the relationship between applied potassium (K) and fruit yield for high tunnel tomato crops using organic sources of fertility. In 2014, indeterminate beefsteak tomatoes were grown in high tunnels in three sites (cv. Geronimo in Durham and North Haverhill, NH and cv. Rebelski in Monmouth, ME). Initial soil K₂O levels averaged 188 mg/kg Mehlich-3 extractable K in Durham, NH, 176 mg/kg in North Haverhill, NH, and 79 mg/kg in Monmouth, ME. Depending on the site, plants received 6 or 7 levels of supplemental K₂O using potassium sulfate (0N-0P₂O₅-54.5K₂O), ranging from 0 to 1,008 kg/ha K₂O. All treatments received constant supplemental nitrogen at 423 kg/ha using a mixture of blood meal and soybean meal. The blood and soy meal provided an additional 122 kg/ha K₂O to all treatment levels. A randomized complete block design with 4 to 6 replicates was used. Yields of marketable and unmarketable fruit were measured and petiole sap K levels were measured mid-harvest and at the end of the growing season. Supplemental K levels were highly correlated with midseason soil K levels in all sites. Supplemental K levels were not correlated with midseason petiole sap K levels, but were correlated with end-of-season petiole sap K levels in all sites. However, supplemental K levels in all sites were not significantly correlated with fruit yield, suggesting that K availability did not limit yields in these experiments. The absence of a strong yield response to K may have been due to high background soil K levels, a relatively short growing season due to late planting, or because K requirements for high tunnel tomatoes are lower than we had hypothesized.