Jr. Schultheis et Rj. Dufault, WATERMELON SEEDLING GROWTH, FRUIT YIELD, AND QUALITY FOLLOWING PRETRANSPLANT NUTRITIONAL CONDITIONING, HortScience, 29(11), 1994, pp. 1264-1268
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.