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

Tomatoes represent about 15% of total vegetable production globally. On average, Virginia farmers produce 1200 to 2500 ha of fresh market tomatoes annually that are worth 50 to 100 million dollars ($US). Tomatoes are produced using polyethylene mulch systems on sandy loam and loamy sand coastal plain soils where potassium (K) and sulfur (S) deficiencies occur, especially with shallow rooted vegetable crops. The objective of this study was to evaluate fresh market tomato response to K, S, Mg, and Ca from granule polyhalite (POLY4) compared to muriate of potash (MOP) and MOP fortified with S and Ca additions (MOP+) on 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. Treatments POLY4 and MOP+ produced significantly higher total and marketable fruit yields than MOP and control. Leaf tissue concentrations indicated higher Mg, S, Mn, and Zn concentrations for POLY4 and MOP+ treatments as compared to MOP at first bloom, which correlated with visual yellowing and lower SPAD readings in plots receiving no S fertilizer (0.39 and 0.37% S vs. 0.32 and 0.30% S for POLY4, MOP+, MOP, and control, respectively; LSD_0.10 = 0.03%). Even though sufficient S was taken up in plant tissue (0.30% S threshold), 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 performs equally well as traditional inorganic fertilizers for fresh market tomato production in the Mid-Atlantic Region, USA.