Tomato Response to Polyhalite Fertilizer on Sandy Loam Soils in the Mid-Atlantic Region.

Tomatoes are the most important vegetable crop globally, making up about 15% of total vegetable production.  Virginia is the third largest producer of fresh market tomatoes in the United States with the main production region located in eastern Virginia. On average, Virginia farmers produce 1200 to 2500 ha of tomatoes annually that are worth 50 to 100 million dollars ($US). Tomatoes are produced on sandy loam and loamy sand coastal plain soils where potassium (K) and sulfur (S) deficiencies are known to occur. The objective of this study was to evaluate fresh market tomato response to K, S, Mg, and Ca from polyhalite in granule form (POLY4) compared to muriate of potash blend (MOP) alone and with MOP fortified with S and Ca additions (MOP+) in sandy loam soils. We applied each fertilizer source at 0, 40, 80, 160, and 240 kg K₂O ha^-1.  The experimental design was a factorial arrangement of 3 sources (POLY, MOP, and MOP+) × 5 rates = 15 treatments arranged in a randomized complete block design with four replications. Leaf tissue, SPAD meter, yield, and residual soil nutrient concentrations were measured. Exponential relationships with total yield indicated greater yields at 240 kg K₂O ha^-1 with POLY4 as compared to MOP and MOP+ (68,815 vs. 60,329 and 61,360 kg fruit ha^-1, respectively). Leaf tissue concentrations indicated higher Mg, S, Mn, and Zn concentrations for POLY4 and MOP+ treatments as compared to MOP, which correlated with visual yellowing and lower SPAD readings in plots receiving no S fertilizer. Even though sufficient S was taken up in plant tissue, significant amounts of S were also still present in soil after tomato harvest with POLY4 treatments having higher concentrations than MOP+ and MOP (0.21 vs. 0.18 and 0.13 mg S kg^-1, respectively). In conclusion, POLY4 fertilizer hold promise for providing ample fertility for necessary nutrients for optimal vegetable production in sandy loam soils in the Mid-Atlantic Region, USA.