Hybrid squash: Responses to nitrogen, potassium, and phosphorus fertilisers on a soil of moderate fertility

Abstract

Hybrid squash (Cucurbita maxima L. cv. Delica) was grown at five levels of nitrogen (N) at each of five levels of potassium (K), and at five levels of phosphorus (P) at each of two levels of N at Pukekohe, New Zealand. Destructive samples were taken on three occasions during early growth and fresh weight, dry weight, and nutrient contents were measured. The fruit was harvested, and yields and nutrient contents determined, when the crop was mature. Nutrient supply strongly affected plant growth and tissue nutrient concentrations measured 16 days after emergence. Growth differences were maintained until harvest, but differences in tissue nutrient concentrations declined during growth. Fruit yields closely reflected the differences in early growth, increasing from 29 to 38 t/ha with N additions up to 160 kg/ha, from 25 to 38 t/ha with K additions up to 320 kg/ha, and from 22 to 45 t/ha with P additions up to 320 kg/ha. Yield differences were mainly attributable to fruit number per plant, rather than to fruit size. Nutrient removals in the harvested fruit were up to N 179, K 203, and P 36 kg/ha.

Hybrid squash: Yield responses to potassium and phosphorus fertilisers at four sites of varying initial fertility

“…Yields were reduced by 10% with initial decrements of NaHC0 3 -soluble P of 17-20 mg/kg. Again, results from an earlier experiment (Buwalda & Freeman 1986) are consistent with those presented here.…”

“…Hence, the crop nutrient status may be diagnosed most reliably during early growth. This is consistent with earlier results that the relative growth rate of squash was affected more by the crop nutrient status within 16 days of crop emergence than during later stages of growth (Buwalda & Freeman 1986). The importance of nutrition during early crop growth stages is further demonstrated by the observation that the yield responses to fertiliser result primarily from effects on fruit number per plant, which presumably is determined no later than flowering (about 45 days after emergence).…”

“…I), the consistency of yield responses to increasing exchangeable K at the various sites suggests that the maximum yield had been attained at site 1. Results from an earlier experiment (Buwalda & Freeman 1986) are also consistent with those presented here, suggesting that the relationship may be used for crops grown in different years.…”

“…A previous study described the yield responses of squash to nitrogen (N), potassium (K), and phosphorus (P) fertilisers on a Patumahoe clay loam of moderate fertility (Buwalda & Freeman 1986). The maximum responses to K and P, however, were not established, and the results were not directly applicable to sites of different initial fertility.…”

“…The declining effects during crop growth of the fertiliser treatments on the soil K and P levels were probably related to equilibration of the fertiliser within the soil; particularly for P, crop removals are relatively low (Buwalda & Freeman 1986). The use in Fig.…”