Soluble Fertilizer at Transplant and Early Season Plastic Mulch Increase Tomato Yield in Soil with Adequate Fertility

Transplant solutions containing soluble phosphorous (P) fertilizers are often recommended for vegetable transplants, regardless of existing soil fertility. This is thought to increase early-season root growth and nutrient uptake. Soil warming, via plastic mulch, is another method to increase early-season root growth and nutrient uptake in vegetables. We examined the interaction between 3 fertilizer treatments applied at transplant (water, 28-0-0 urea ammonium nitrate [UAN], or 10-34-0 ammonium polyphosphate [APP]) under mulched (26 days of black plastic at the beginning of the season) or bare-ground conditions. In a factorial design of these treatments in 2014, ‘Plum Dandy’ tomatoes, marketed as a determinate cultivar, were grown in Waseca, MN in Webster clay loam soil testing high for phosphorus (35 ppm). Plastic mulch increased 10-cm soil temperature by 1.1º C. An unusually cool summer and early frost caused a late and abbreviated harvest. Mulched plants flowered an average of 27 days after transplant (DAT), and un-mulched plants flowered 29 DAT. Plants fertilized at transplant flowered less than 1 day earlier than un-fertilized transplants. Cumulative mass of fruit harvested at ripeness stage 4, 5, or 6 was 6.0 kg from plants treated with APP at transplant, and 5.0 kg from plants treated with water at transplant. Plastic mulch increased total cumulative yield by 34%. At the final harvest before frost, substantially less green fruit weight remained on plants fertilized with APP and grown with early-season plastic mulch (58%) compared to APP-fertilized un-mulched (64%) or un-fertilized mulched (63%) transplants. Results of UAN fertilizer treatments were intermediate between water and APP treatments.