SUGARBEET RESPONSE TO VARIOUS
SOIL NITROGEN LEVELS

Larry J. Smith
Northwest Experiment Station
University of Minnesota, Crookston

The production of high-yielding, high-quality sugarbeets is strongly influenced by the nitrogen fertilization program chosen. Sugarbeets are a "nitrogen sensitive" crop. Numerous studies point to the need for adequate nitrogen to achieve maximum tonnage and point to the disastrous effects of excess nitrogen on quality, if excess nitrogen remains once that tonnage maximization has been achieved. Selecting the proper nitrogen program is not always easy. Besides nitrogen, management practices, variety selection, and the weather during the growing season will influence the overall quality of the sugarbeet crop produced.

The increasing costs of production are dictating better management practices. Sugarbeet seed companies are releasing varieties with improved quality. With payments to the producer now based on production of a high-quality product, rather than on just tons produced, the nitrogen fertilization program needs to be fine-tuned so as to hit an equilibrium where tonnage plus quality produce maximum return/acre.

The objective of this long-term trial is to determine the nitrogen level needed to maximize dollar return/acre for the producer and production of a high-quality processing product for the processor.

Procedure:
Nitrogen response trials were conducted at Crookston, Minnesota from 1977-84. The number of treatments varied from year to year based on the level of available soil nitrogen present in the top 24 inches of the soil profile. Each year of the trial, 40 soil cores were pulled from the test area, dried, ground and analyzed for available soil nitrate-nitrogen. The amounts of available nitrogen, the soil type of the test site, the planting date and the variety grown are shown in Table 1.
Five nitrogen levels (soil and added) were common to the 8 years this trial has been conducted (Table 3).

All treatments were hand-thinned to uniform plant populations of either 100 (77-78) or 150 (79-84) plants/100 foot of 22-inch row.

Quality data was determined at the American Crystal Quality Lab.

Results:
Increasing the nitrogen rate over 125 lb/acre had non-significant effects on yield but significantly reduced sugar content and recoverable sugar/ton in 1984 (Table 2). Based on current pricing systems (recoverable/ton or recoverable/acre) the 100 lb/acre nitrogen level would have returned maximum gross dollars/acre.

Averaged over 8 years, increasing the soil nitrogen from 100 to 200 lb/acre had nonsignificant effects on yield but significantly reduced the quality factors (Table 3). Based on a quality payment system, such as Phase II adopted by the American Crystal Sugar Co-op., the gross dollars return/acre was essentially the same for the 100 and 125 lb/acre nitrogen rates. As the rates were increased above the 125 lb/acre level, losses of $49-$109/acre occurred. In addition to losing return/acre at these higher nitrogen levels, the producer has added fertilizer and hauling costs for which there is no return.

Results of the individual trials from 1977-84 for the various nitrogen levels are shown in Table 4.

Discussion and Summary:
The need for improved nitrogen management is becoming increasingly clear with the adoption of sugarbeet payments based on quality rather than tons produced. Not only does the producer need to be concerned about the immediate nitrogen application, but must also be concerned about past applications on other crops, mineralization of organic matter in years when the soil is fallowed and leaching of nitrogen to the deeper depths in the soil profile, which the sugarbeet plant readily utilizes.

In 1985 the grower planning to produce beets on acres that were fallowed under the 1983 and 1984 PIK programs will face major hurdles in nitrogen management in some cases. Many of these acres are testing over 175 lb/acre nitrate nitrogen in the top 24 inches and have additional nitrogen which has leached below this standard soil testing level which will be available to the sugarbeet crop. Based on the 8 years of data from the trial there is a potential loss on these fields of $60-$110/acre due to excess nitrogen. The exact loss will be extremely dependent on the 1985 growing conditions.

The nitrogen level recommended by the University of Minnesota, North Dakota State University, sugar cooperatives, and many other private soil testing labs are well within the range needed to maximize return/acre, provided the producer sets a realistic yield goal on which the recommendation is made. A realistic yield goal is in the 17-18 ton/acre range. If nature provides moisture, temperature, and the growing season to produce a crop greater than this range, mineralization that occurs in our high organic matter soils will provide the excess nitrogen to produce such a crop in most cases. Additionally, numerous methods are available to add nitrogen to the crop during the growing season should this ever become necessary.

1984 Sugarbeet Research and Extension Reports. Volume 15, pages 77-80.

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