Yield Response of Winter Squash to Irrigation Regime and Planting Density

Consumers are increasingly interested in buying local vegetables in the fall and winter. Winter squash is an important vegetable crop for local and regional fall and winter markets, and consumers are increasingly seeking high-culinary value Cucurbita maxima types such as kabocha and buttercup. Although consumer demand for kabocha and buttercup squash is increasing, Oregon farmers report they are marginally profitable. The goals of this project were 1) to identify productive kabocha and buttercup varieties for western Oregon when grown with or without overhead irrigation and 2) to describe the effects of planting density on yield, fruit weight, number of fruit per hectare, and fruit per plant. Seven varieties of C. maxima winter squash, including kabochas and buttercups, and one interspecific (C. maxima 3 C. moschata) hybrid 'Tetsukabuto' were grown in a split-split plot randomized complete block design experiment with irrigation as the main plot, planting density as the subplot, and variety as the sub-subplot. Four replications of four different planting densities for eight varieties were grown in 2016 and 2017. Irrigated planting densities ranged from 8611-32,292 plants/ha (0.86-3.2 plants/m(2)) and dryland planting densities ranged from 3827-14,352 plants/ha (0.38-1.4 plants/m(2)) in 2016 and 5741-21,528 plants/ha (0.57-2.2 plants/m(2)) in 2017. The seven C. maxima types had statistically comparable yield under both irrigated and dryland production, with an average yield of 33.9 t.ha(-1) with irrigation and 19.4 t.ha(-1) without irrigation. Dryland yields in 2016 and 2017 were 76% and 37% of irrigated yields, respectively. 'Tetsukabuto' had the greatest yield (mean, 51.4 t.ha(-1)), the greatest number of fruit per hectare (mean, 12,080), and the greatest number of fruit per plant (mean, 1.94) when grown with irrigation, and yielded comparably with other varieties when grown in dryland production. Planting density impacted the fruit weight, number of fruit per hectare, and number of fruit per plant, although it did not impact yield statistically in both irrigated and dryland production. Average fruit weight decreased linearly from 1.89 to 1.30 kg for the irrigated trials, from 2.04 to 1.56 kg in the 2016 dryland trial, and from 1.42 to 0.93 kg in the 2017 dryland trial as planting density increased from 0.86 to 3.2, 0.38 to 1.4, and 0.57 to 2.2 plants/m(2), respectively. The number of fruit per hectare increased linearly from 6660 to 10,590 as the number of plants per hectare increased from 8611 to 32,292 plants/ha for the irrigated trials, because even at the lowest planting density, plants did not produce more than two fruit per plant on average across varieties when grown with irrigation. Farmers can manipulate squash fruit size to suit market preferences by changing planting density. The very low 2017 dryland yields were likely a result of unusually high summer temperatures in western Oregon. Increasingly hot summers may render dryland squash production unfeasible in this region.