SPATIAL AND TEMPORAL DISTRIBUTION OF ¹⁵N TRACER AND TEMPORAL PATTERN OF N UPTAKE FROM VARIOUS DEPTHS BY SUGARBEET

Abstract

Assessment of nitrogen (N) fertilizer needs for sugarbeet requires knowledge of the amount of N available from the soil including the profile below the plow layer. Field studies were conducted to examine 1) spatial and temporal distribution of ¹⁵N tracer applied at different soil depths and 2) temporal pattern of N uptake by sugarbeet from various depths. Tracer ¹⁵N 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 surface and at depths of 30, 60, 90, 120, and 150 cm. Sugarbeet plants were collected 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 ¹⁵N 10 cm from the point of injection was detected at the 75 and 120 cm depths 8-weeks after planting. Tracer N was recovered from all depths 9 weeks after planting but greatest amounts were recovered from the top 30-cm depth of soil throughout the sugarbeet growing season. 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 preferentially utilized in sugarbeet nutrition.

ACKNOWLEDGMENTS

The authors are grateful to Michigan Sugar Company and Monitor Sugar Company for the financial support. Appreciation is expressed to Mr. Clavin E. Bricker and Mr. Richard E. Schmenk for their assistance with the field studies.