ASHS 2015 Annual Conference

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.