ChileanJAR

“Summer squash” (Cucurbita maxima var. zapallito (Carr.) Millán) is a monoecius species and the reproductive stage starts with female flowering. A male to female flower ratio lower than 10:1 results in greater fruit setting and yield. This relation is controlled by environmental factors, growth hormones and nutrients. The aim of this study was to evaluate the effect of the N:K ratio on sex expression, fruit setting, earliness and yield on the summer squash. Before emergence 50 kg P ha^-1 was applied, after that N and K were applied to get the following relations: 50N:0K, 50N:50K, 50N:100K. Male and female flowering dates were recorded, and the flowering rate and the male to female flower ratio was calculated. Fruit set and marketable fruit number, days to harvest, fruit per plant, mean fruit weight and yield were determined. The number of flowers was greater for the relations 50N:50K and 50N:100K than for 50N:0K. The increment in the K fertilization did not affected the number of male flowers, but decreased the male to female flower ratio due to higher female flower production. The number of fruit set was lower at 50N:0K, without significant differences between 50N:50K and 50N:100K. The highest early yield was obtained with 50N:50K and 50N:100K, with respect to 50N:0K. The highest marketable yield was obtained with 50N:100K because of a greater marketable fruit number, since there was no significant fruit weight difference with fertilization.