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  • Author or Editor: Laura L. Van Eerd x
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With rising input costs and environmental concerns, growers are seeking methods to minimize nitrogen (N) inputs and off-field N losses while maintaining crop yields. Field studies on processing butternut squash (Cucurbita moschata Duchesne ex Poir.) were conducted in 2004–2007 at 11 locations in Ontario, Canada, to determine the optimal N rate and estimate potential N losses. Preplant broadcast ammonium nitrate was applied at five rates between 0 and 220 kg N/ha. In contrasting years (i.e., cool/wet versus warm/dry versus average), 64% of sites were nonresponsive to N fertilizer as indicated by no differences in marketable squash yield. In responsive sites, the most economical rate of N (MERN) was between 105 and 129 kg N/ha of N fertilizer, indicating that the Ontario-recommended rate of 110 kg N/ha seems appropriate for responsive sites. At 110 kg N/ha, no yield advantage resulted from using a controlled-release N (CRN) or split-applying ammonium nitrate at preplant and vine elongation at 65 + 45 kg N/ha, respectively, compared with the same amount applied preplant. Apparent N losses (N inputs – N outputs) at harvest were 83 and 29 kg N/ha greater at a fertilizer application rate of 220 kg N/ha than at 0 and 110 kg N/ha, respectively. At 110 kg N/ha, crop removal balance and apparent N loss calculations suggest relatively low risk of N loss from the field during the growing season and after harvest, respectively. However, environmental and economical risks would be minimized if nonresponsive sites could be identified before N fertilizer application.

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The increase in fertilizer costs as well as environmental concerns has stimulated growers to re-evaluate their fertilizer applications to optimize nitrogen use efficiency (NUE) while maintaining crop yields and minimizing N losses. With these objectives, field trials were conducted at seven sites with five N rates (0 to 220 kg N/ha) of ammonium-nitrate applied preplant broadcast and incorporated as well as a split application treatment of 65 + 45 kg N/ha. In three contrasting years (i.e., cool/wet versus warm/dry versus average), N treatment had no observable effect on grade size distribution or brine quality. Based on the zero N control treatment, the limited yield response to fertilizer N was the result of sufficient plant-available N over the growing season. In the N budget, there was no difference between N treatments in crop N removal, but there was a positive linear relationship between N applied and the quantity of N in crop residue as well as in the soil after harvest. As expected, apparent fertilizer N recovery and N uptake efficiency were lower at 220 versus 110 kg N/ha applied preplant or split. The preplant and split applications of 110 kg N/ha were not different in yield, overall N budget, or NUE. Considering the short growing season, planting into warm soils, and the generally productive, nonresponsive soils in the region, growers should consider reducing or eliminating fertilizer N applications in machine-harvested cucumber.

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