Determining Nitrogen Fertilizer Needs for Sugarbeets from Residual Soil Nitrate and Mineralizable Nitrogen 1

Soil nitrate and mineralizable nitrogen are used to predict the root yield potential and N fertilizer needs of sugarbeets. Predicting the required N fertilizer for optimum refined sucrose production based on soil test procedures is needed because inadequate N limits root yield and high levels of N may reduce both extractable sucrose and sucrose yield. Sugarbeets ( Beta vulgaris L.) were grown at 14 residual and fertilizer N rates to determine the root yield, sucrose percentage, sucrose yield, and N uptake in relation to the residual, mineralizable, and fertilizer N. A soil test to measure both the mineralizable and NO 3 ‐N level of a soil was found to serve as a valuable guide in recommending N fertilizer for sugarbeets. The amount of N supplied from mineralizable sources in a uniformly cropped and fertilized field is expected to remain reasonably constant if adequate but not excess N fertilizer is supplied each year to the crop grown. Therefore, repeating the test for mineralizable N each year may not be necessary. Determining the amount of NO 3 ‐N in the root zone, which is now feasible with rapid and accurate methods of soil analysis, combined with the predetermined mineralizable N, would increase the accuracy of N fertilizer recommendations.