WATERMELON SEEDLING GROWTH, FRUIT YIELD, AND QUALITY FOLLOWING PRETRANSPLANT NUTRITIONAL CONDITIONING

Pretransplant nutritional conditioning (PNC) of transplants during gre enhouse production may improve recovery from transplanting stress and enhance earliness and yield of watermelon [Citrullus lanatus (Thumb.) Matsum. and Nakai]. Two greenhouse experiments (Expts. 1 and 2) and fi eld experiments in South Carolina and North Carolina (Expt. 3) were co nducted to evaluate N and P PNC effects on watermelon seedling growth and their effects on fruit yield and quality. 'Queen of Hearts' triplo id and 'Crimson Sweet' diploid watermelon seedlings were fertilized wi th N from calcium nitrate at 25, 75, or 225 mg.liter(-1) and P from ca lcium phosphate at 5, 15, or 45 mg.liter(-1). In the greenhouse, most variation in the shoot fresh and dry weights, leaf count, leaf area, t ransplant height, and root dry weight in 'Queen of Hearts' and 'Crimso n Sweet' was attributed to N. Cultivar interacted with N, affecting al l, seedling growth variables, but not leaf area in Expt. 2. To a lesse r extent, in Expt. 1, but not in Expt. 2, P interacted with cultivar, N, or cultivar x N and affected shoot fresh and dry weights, leaf coun t and leaf area. In the field, transplant shock increased linearly wit h N, regardless of cultivar or field location. The effect of PNC on pl ant growth diminished as the growing season progressed, For both culti vars at both locations, N and P PNC did not affect time to first stami nate flower, fruit set, fruit width or length, soluble solids concentr ation, or yield. Vining at Charleston for both cultivars was 2 days ea rlier when N was at 75 rather than 25 mg.liter(-1), without further ch ange with the high N rate. At Clinton, the first pistillate flower was delayed linearly the higher the N rate for 'Crimson Sweet'. At Charle ston, hollow heart in the 'Queen of Hearts' increased nearly 3 times w hen N PNC rate was tripled (from 75 or 225 mg.liter(-1)), while N had no effect on hollow heart in 'Crimson Sweet'. In contrast, at Clinton, hollow heart in either cultivar was affected by P PNC, not N. PNC wit h 25N-5P (in mg.liter(-1)) can be used to reduce seedling growth and p roduce a more compact plant for easier handling, yet not reduce fruit quality or yield.