We sometimes hear that excessive nitrogen could delay fruit set, stimulate excessive vine growth, and depress overall yield of pumpkins, but it is often unclear how much nitrogen is too much. This article reviews research on nitrogen fertilizer rates for pumpkins, and discusses the potential factors that might affect the recommended nitrogen rate.
In a study conducted in 1987 and 1988 in Kilbourne, IL, four nitrogen rates were compared: 50, 100, 150 and 175 lb N/acre. The first three rates (50, 100 and 150 lb N/acre) were applied through fertigation, while the highest rate (175 lb N/acre) was applied preplant and about a month after seeding. The study found the highest early and total marketable yields were obtained with fertigation of 100 lb N/acre. The lowest total yield was associated with the lowest nitrogen rate (50 lb N/acre). Fertigation with 150 lb N/acre and dry-blend with 175 lb N/acre delayed the start of flowering and reduced marketable yield.
In another study conducted in 1995 in Geneva, N.Y, three nitrogen rates (60, 100 and 140 lb N/acre) were compared. All the fertilizers were preplant applied and sidedressed when vines began to run. Interestingly, there was no difference in yield among the three nitrogen treatments. As the year was very dry, the author suggested higher yield might be expected from additional N input if there was more soil moisture.
In the third study conducted in 1996 and 1998 in Champaign, IL. Five N rates (0, 50, 100, 150 and 200 lb N/acre) were applied following each of the four cropping systems: 1) pumpkins following corn, 2) pumpkins following soybeans, 3) pumpkins following 2-years corn, and 4) pumpkins following fallow ground. Models were established. According to that, optimal N rate for pumpkins following soybean was 100 lb N/acre, following fallow ground was 115 lb N/acre, following corn was 134 lb N/acre and following 2-years of corn was 159 lb N/acre.
A more recent study on no-till pumpkins was conducted in 2003 in Waynesville, NC. Rye and wheat cover crops that were killed with paraquat before planting were used as covers. Nitrogen fertilizers at four rates (0, 36, 71, 107 lb N/acre) were broadcast applied. The highest rate (107 lb N/acre) applied maximized pumpkin yield. The author suggested that higher yield might be possible with even greater N rates. This study indicated that more N fertilizers are needed in no-till pumpkins than conventional tillage pumpkins.
As we can see from the research, optimal N rates are related to several factors such as fertilizer application methods, soil moisture level, previous crops, production system etc. Although we can not provide a cut-off number in the case of how much nitrogen is too much, hopefully, this literature review will be helpful for you to decide the fertilizer rate for pumpkins.