Spatial and temporal distribution of N-15 tracer and temporal pattern of Nuptake from various depths by sugarbeet

Assessment of nitrogen (N) fertilizer needs for sugarbeet requires knowledg e of the amount of N available from the soil including the profile below th e plow layer. Field studies were conducted to examine 1) spatial and tempor al distribution of N-15 tracer applied at different soil depths and 2) temp oral pattern of N uptake by sugarbeet from various depths. Tracer N-15 was applied in confined spots at depths of 30, 75 and 120 cm. Soil samples were collected at 5, 8 and 16 weeks after planting and analyzed for atom excess and mineral N. For the second objective, tracer N was applied on the surfa ce and at depths of 30, 60, 90, 120, and 150 cm. Sugarbeet plants were coll ected 3. 6, 9. 12. 15, and 18 weeks after planting. Soil mineral N declined with time at all depths and the decline was most pronounced at 30-cm deep. Lateral movement of tracer N-15 10 cm from the point of injection was dete cted at the 75 and 120 cm depths 8-weeks after planting. Tracer N was recov ered from all depths 9 weeks after planting but greatest amounts were recov ered from the top 30-cm depth of soil throughout the sugarbeet growing seas on. Nitrogen uptake by sugarbeet was mostly from the surface and 30 cm deep . The findings of this study suggests that while sugarbeet recovers N from far below the plow layer the N available in or near the top 30 cm is prefer entially utilized in sugarbeet nutrition.