WATERMELON YIELD AND QUALITY: EFFECT OF FERTILIZER RATE AND PLACEMENT

Yield, soluble-solids content, and blossom-end rot were determined for 'Charleston Gray' and 'Smokylee' watermelon from NPK fer tilizer trials on Astatula fine sand near Leesburg in 1969-1971. When high rates of N and K were applied in a band soluble salt injury reduced early yield. On the deep, well-drained sands plants recovered from early injury and total yield was relatively unaffected by placement of preplant fertilizer. Based on yield and tissue P, the avail ability of P to the plant was not increased by banding fertilizer P. When only P fertilizer was banded, N and K fertilizer rate had more effect on tissue P than rate of fertilizer P. High rates of fertilizer N and K resulted in a high concentra tion of P in the tissue and was probably indicative of optimum uptake of the three fertilizer nutri ents. Low tissue Ca was not related to blossomend rot. The soluble salts content of mature 'Smokylee' melons was consistently higher than that of 'Charleston Gray' but, generally, fertilizer rate and placement had little effect on the solublesolids content of the melons. A common practice in watermelon production in the past has been to place the preplant fertilizer in a 10-inch (24 cm) band 6 inches (15 cm) below the center of the bed. However, under certain con ditions, soluble salt injury to the young water melon seedling has occurred. Increasing the appli cation rate of a 6-3.5-6.7 (N-P-K) all mineral fer tilizer from 1000 to 2000 lb/acre (1120 to 2240 kg/ha) resulted in increased watermelon yields when preplant fertilizer was broadcast but re duced yields when applied in a broad band (4). Similar occurrences of salt injury to young water melon seedlings (10, 11) have resulted in the cur rently recommended practice in Florida that pre plant fertilizer be broadcast over the bed area and incorporated prior to bedding. Workers in some areas found more efficient use Florida Agricultural Experiment Stations Journal Series No. 5163. of fertilizer P when P was banded near the seed than when broadcast and mixed with a large vol ume of soil (7, 13, 14). Recent work on sandy soils (2, 4, 6, 9, 10) indicated that plant growth and yield of field corn, potatoes, and watermelon were at least as good with broadcast as with band application of preplant fertilizer. Generally, effects of fertilizer placement on nutrient content of watermelon tissue were not consistent at various sampling times or from year to year (3, 5, 11). At layby, however, tissue K tended to be higher when fertilizer was broadcast than when banded. With low soil P, tissue P tended to be higher when fertilizer P was banded than when broadcast (3). High rates of fertilizer K significantly reduced tissue Ca and decreased tissue Mg. Since low Ca levels have been associated with blossom-end rot (BER) in tomato (8) and watermelon (1), the antagonistic effect of high levels of N and K may increase the incidence of this physiological disorder. The purpose of this work was to study the effects of rate and placement of preplant fertilizer, especially the placement of fertilizer P, on yield and quality of watermelons. Materials and Methods Fertilizer trials were conducted in 1969-1971 on Astatula fine sand at the Agricultural Research Center, Leesburg. In the 1969 and 1970 trials (3) the preplant fertilizer was all banded or all broad cast and in 1971 the trial included a treatment in which only the P was banded and the N and K were broadcast. Treatments were arranged in a randomized complete block design with each treat ment replicated 5 times in 1969 and 4 times in 1970 and 1971. In all 3 years fertilizer N, P, and K were ap plied at the following 4 rates: 120-53-100, 240-53200, 120-106-100, and 240-106-200 lb/acre (134-59112, 268-59-224, 134-118-112, and 268-118-224 kg/ ha). All P fertilizer and half of the N and K were applied preplant either in a 10-inch (25 cm) band 6 inches (15 cm) below the surface of the planting bed or broadcast in a 40-inch (1 m) swath and in corporated prior to forming the bed. The remain ing N and K fertilizer was applied at emergence (17 kg N and K/ha) and at layby. The 2-row plots, 20 x 24 ft (6.1 x 7.3 m), were ELMSTROM, ET AL: WATERMELON FERTILIZATION 197 Table 1. Effects of fertilizer treatment on soluble salt concn in the soil at layby and on the combined early and total yields of'Charleston Gray'and'Smokylee'watermelon in 1969 and 1970. Fertilizer treatment Soluble salts Yield (tons/acre)y