PUMPKIN GROWTH, FLOWERING, AND FRUITING RESPONSE TO NITROGEN AND POTASSIUM SPRINKLER FERTIGATION IN SANDY SOIL

Field studies were conducted in 1987 and 1988 to determine the effect of various sprinkler-applied N-K fertigation treatments and 196N-280K (kg.ha-1) dry-blend application on pumpkin (Cucurbita moschata Poir.) flower development, fruit set, vine growth, and marketable yield respo nse in a Plainfield sand. The number of male and female flowers that r eached anthesis by 72 days after seeding (DAS) was highest with either 112N-112K or 112N-224K fertigation. Fertigation using either 56N-112K or 168N-224K delayed the start of flowering and reduced the total num ber of male and female flowers produced by 72 DAS. Fruit set decreased at the low N-K fertigation rate (56N-112K), but otherwise was unaffec ted by N-K fertility regime. Vine dry weight and stem elongation incre ased as the N fertigation rate increased, with relatively little effec t from fertigated K. There was no field indication of excessive vegeta tive growth in any of the fertigation treatments. Highest yields of ea rly set marketable fruit (pumpkins that set before 65 DAS), and total marketable yields were obtained with fertigation of 112N, in combinati on with either 112 or 224 kg.ha-1 fertigated K. Usable green and cull fruit production increased with increasing N-K fertigation rate. Dry-b lend application of 196N-280K decreased early and total yields signifi cantly. The results showed that sprinkler-applied 112N-112K split into rive fertigations during the growing season (supplemented with a prep lant dry-blend application of 28N-56K) produced high yields without co mpromising early fruit maturity.