The effects of supplemental Ca and varying NO3:N H4 ratios on transplant growth and NH4-N utilization were studied using watermelon (Citrullus vulgaris L. `Crimson Sweet') seeded in plastic multicell trays. The growing media consisted of a commercial peat mix amended with CaCO3 (10% w/v). Fertigation with five NO3:N H4 ratios and five levels of supplemental Ca (4, 8, 12, 16 mmol.) was applied daily in factorial combinations. The highest NO3:N H4 ratio produced greatest shoot dry weight, shoot N, and shoot NO3-N and K concentrations. Increasing NH4 and Ca decreased media pH and increased EC. After 21 days, supplemental Ca decreased shoot N and dry weight, but after 28 days had no effect. Additional Ca increased shoot Ca but decreased Mg and K. Supplemental Ca and N ratio interacted to affect leaf area. Pretransplant N ratio and supplemental Ca effects on seedling field performance, flowering, and yield were evaluated.
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