Predicting Nitrogen Fertilizer Needs for Sugarbeets from Residual Nitrate and Mineralizable Nitrogen'

Received for publication ply 8, 1974 Nitrogen (N) fertilizer management for sugarbeet (Beta vulgaris L.) production requires more precise information than for most crops. Inadequate N limits plant growth and root yield, but excess N may reduce both sucrose percentage and recoverable sucrose (7)." Also, excess N may stimulate more leaf growth than necessary. The rate and timing of N fertilizer applications are not only important in supplying crop N needs, but can influence the amount of N lost by leaching and denitrification. Soil and plant tissue tests can provide essential data For decision-making for efficient and economical use of N fertilizer. Recent studies have shown that the NO3-N level in the soil before planting is closely related to sucrose production when N is limiting (8, 12). Inclusion of the N mineralization capacity of the soils would be expected to improve the relationship. Stanford and Smith (14) showed that the mineralization capacity varies with soil type and location. Therefore, a soil test for N that would have general applicability should include the mineralization capacity of the soil, and the interpretation of these tests should include some knowledge of expected irrigation practices. A soil test for NO3-N may suffice as an index of N fertilizer needs for a given soil and irrigation level. Recently, Carter et al. (5) showed that sucrose production was closely related to available soil N, as indicated by a soil test that included both mineralizable N and NO3-N. The objective of our study was to evaluate the soil test-yield relationship, developed from experimental data at one location in south central Idaho, for predicting N fertilizer needs throughout southern Idaho under various irrigation management practices.