Sugarbeet nitrogen uptake and performance following heavily fertilized onion

Crop over-fertilization has economic and environmental consequences. Sugarbeet (Beta vulgaris L.) N fertilizer requirements could be lower than expected when planted after shallow rooted onion (Allium cepa L.). Sugarbeet was planted on an Owyhee silt loam (coarse-silty, mixed, mesic Xerollic Durorthid) for 2 yr, where the previous onion crop had received 0, 60, 120, 240, and 480 kg N ha -1 . . Soil nitrate and ammonium were measured in 0.3-m increments to 1.8 m deep after harvesting onion, and before and after growing sugarbeet. Nitrogen uptake by plant parts, and beet and sucrose yields, were measured. Averaged across years, sugarbeet recovered 336, 316, 338, 400, and 505 kg N ha -1 when N fertilizer of the previous onion crop was 0, 60, 120, 240, and 480 kg ha -1 , respectively. The corresponding reduction in available inorganic N from the top 1.8 m of the soil during sugarbeet growth was 27,82,62,120, and 152 kg ha -1 , Nitrogen recovered by sugarbeet was largely supplied by sources other than preplant available N. Recovered sucrose yield was near maximum when the N rate on the previous onion crop was 240 kg ha -1 , which resulted in preplant NO 3 -N levels of about 70 kg ha -1 in the top 0.6 m of the soil. Sucrose yield did not improve when petiole NO 3 -N in late June exceeded 6 g kg -1 . In conclusion, sugarbeet may not require fertilizer N when grown after onion fertilized with about 240 kg N ha - 1 .