Muskmelon Response to Rates and Sources of Nitrogen

The method and rate of nitrogen fertilization of muskmelons (Cucumis melo) on sandy soils is of concern because of the leaching potential of N. The relative availability of nitrogen from ammonium nitrate, urea-formaldehyde, and sulfur coated urea (SCU) was studied the field with regard to influence on growth, leaf and petiole composition, and fruit yield of muskmelon. The field studies compared various nitrogen materials in different timing and rate schedules. The fertilizers were used at 0, 33, 66, 99, 132, and 264 kg/ha in single (preplant) and split (preplant + sidedressing) applications. Data were collected for 4 seasons. In each year N application increased vine growth and intensity of the green color of the leaves. The N concentration of the recently mature melon leaves was increased more by NH₄NO₃ than by urea-formaldehyde or SCU. The relationship of N rate was linear with N composition but parabolic with yield. Optimum plant growth and fruit yields were obtained with a preplant application of 80 to 90 kg/ha. The same total N rate as a split application or as a less available N source was not as effective for fruit yield production. The increased yield from N treatment was due to increased vine size and increased numbers of fruit. Optimum fruit yields were produced at leaf composition of total N over 4.5% or petiole content of NO₃-N over 15,000 ppm during vegetative and fruit initiation stages. Sulfur coated urea with 37% dissolution rate produced NO₃-N and total N concentrations of petioles about equal to the same N rate as NH₄NO₃; SCU with 12% dissolution rate resulted in NO₃ concentrations equal to one-quarter the N rate as NH₄NO₃ at the runner stage and equal to one-half the N rate as NH₄NO₃ just prior to harvest. Ammonium nitrate, a soluble, immediately available N source, applied in preplant at 80 to 90 kg/ha was the most effective treatment and resulted in optimum muskmelon fruit yields on sandy soils of southwestern Indiana in each year of the study.