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A canopy approach to nitrogen fertilizer recommendations for the sugar beet crop

Malnou, C.S., Jaggard, K.W., Sparkes, D.L.
European journal of agronomy 2006 v.25 no.3 pp. 254-263
Beta vulgaris, sugar beet, nitrogen fertilizers, fertilizer rates, remote sensing, fertilizer requirements, canopy, field experimentation, plant nutrition, nutrient uptake, crop yield, vegetation cover, crop models, heat sums, soil fertility, mineral soils, organic fertilizers, mineral fertilizers, United Kingdom
This study investigated whether the main role of nitrogen (N) fertilizer in the sugar beet crop is to allow a full canopy to grow quickly, and whether the minimum amount to achieve this is the optimum dose of N fertilizer. Five field experiments were carried out at four sites within the UK to determine the smallest N fertilizer rate which is the first to produce 85% canopy cover and to compare this with the optimum N fertilizer rate for maximum sugar yield. The experiments tested fertilizer treatments, which ranged from 0 to 160 kg N ha-1. Canopy cover was assessed throughout the season, N uptake measured and sugar yield determined. A canopy model fitted the data well and was used to determine the smallest amount of N to reach 85% cover soonest. These crops needed ca. 900 °Cd from drilling and an uptake of ca. 100 kg N ha-1 to reach 85% cover. Until July, the N uptake was hardly affected by variations in soil N, so canopy cover at 900 °Cd could not be predicted from measurement of soil mineral N and N fertilizer applied across sites. The yield response to N fertilizer was a split line response. Across sites, the smallest dose of N fertilizer which was the first to produce 85% canopy cover was no better a predictor of the optimum dose of N than published recommendations. Rather, the results suggest that in mineral soils, soil mineral N assessments do not improve accuracy of fertilizer recommendations for sugar beet and that, in the absence of organic manure, 100 kg ha-1 should be applied for maximum yield.