Sugarbeet response to broadcast and starter phosphorus applications in the Red River Valley of Minnesota

Field trials were conducted over eight site-years in the Red River Valley of Minnesota to test sugarbeet (Beta vulgaris L.) response to broadcast and starter P fertilizer. Experimental sites were selected based on low soil test P (≤7 mg P kg^-1 Olsen P) and soil textures ranging from sandy loam to silty clay. Incremental P fertilizer rates from 0 up to 102 kg P₂O₅ ha^-1 were broadcast and incorporated before planting sugarbeet with or without 14 kg P₂O₅ ha^-1 liquid starter (14-L) applied directly to the seed. Eighteen and 22 kg P₂O₅ ha^-1 as liquid starter (18-L and 22-L) and two rates of dry starter (14-D and 18-D) with 0 broadcast P were also applied directly to the sugarbeet seed at planting. High rates of starter tended to reduce sugarbeet seedling emergence up to 22%, but the effects of 14-L were minimal. There were no significant effects of the treatments on sugarbeet root quality, which ranged from 132 to 180 kg recoverable sucrose Mg-1 over the eight site-years. Root yield and recoverable sucrose ha^-1 obtained with 14-L starter alone matched or exceeded that obtained with any other treatment. Over eight site-years, 14-L starter alone produced 45 to 65 Mg ha^-1 root yield and 6 to 11 Mg ha^-1 recoverable sucrose, which was not increased with additional P as either broadcast or starter fertilizer. The enhanced productivity with 14-L starter was evident soon after seedling emergence and was measurable 40 d after planting.