FERTILIZING
SUGARBEETS

Profitable sugarbeet production depends largely on a high sucrose content high tonnage crop. To accomplish this, growth-limiting factors such as soil fertility must be managed effectively.

Sugarbeets are unique in their nitrogen (N) requirements. Too little nitrogen results in poor leaf canopies, premature yellowing and reduced yields,while too much nitrogen leads to a reduced sucrose content, increased impurities and lowered sucrose extraction. For proper nitrogen management, pregrowing season soil nitrate-nitrogen (NO₃-N) should be determined in a reputable laboratory that uses recognized procedures and interpretations. Because of the mobility of soil NO₃-N, test each year for nitrogen recommendations and every three or four years for phosphorus and potassium.

NITROGEN AND QUALITY:
Sugarbeet quality involves two concepts: the percent sucrose in the root and the level of impurities in the root, both of which affect sucrose extraction by the processor. Production of high quality sugarbeets is especially important to growers being paid on the extractable sucrose content of their beets.

Proper nitrogen fertilizer use normally increases yield of both roots and sucrose. It also increases impurities and decreases the percentage of sucrose in

the root. Use soil test information to select fields with nitrogen levels suited to expected yields, or to make fertilizer recommendations for expected yield goals. Excessive use of nitrogen fertilizer usually lowers beet quality significantly.

YIELD GOALS:
When selecting a sugarbeet yield goal and requesting fertilizer recommendations, remember that recoverable sugar is the product desired. Over fertilization, particularly with nitrogen, can result in poor quality beets and reduced net returns. Therefore, judicious use of manageable factors such as nitrogen fertilizer, early planting, even spacing, adequate plant populations, weed control, timeliness of operations, disease and insect control will all improve recoverable sugar yield. A good method for selecting a yield goal is to aim for a yield within three tons of the greatest yield produced on your farm.

YIELD GOALS ABOVE 22 TONS:
Although the recommendation tables only go to 22-ton yield goals, we know that it sometimes is possible to grow more than 22 tons of beets per acre in Minnesota and North Dakota. When adequate nitrogen is applied for greater yield goals the chances of having low sugar and high impurities greatly increase. When growing season rainfall is sufficient for yields above 22 tons, increased mineralization of nitrogen from organic matter should occur to provide nitrogen for greater yields.

FERTILIZATION RECOMMENDATIONS:
Table 1 shows the amount of soil NO₃-N in the top2 feet of soil, plus nitrogen fertilizer needed to meet the requirements for various sugarbeet yield goals. These data are based on soil NO₃-N levels as determined from analysis of samples taken between September 1 and April 1. It is strongly recommended soil samples not be taken before September 1 or until soil temperatures are 50°F or less.

To determine fertilizer nitrogen requirements, find the amount of soil nitrogen plus nitrogen fertilizer needed for your yield goal in Table 1 and subtract the soil level of NO₃-N.

As an example, an NDSU soil test indicates there are 50 pounds of NO₃-N present in the top 2 feet of soil. With a yield goal of 16 tons per acre the fertilizer application should equal 45 pounds actual nitrogen per acre - the difference between 95 pounds (taken from Table 1) and 50 pounds from the soil test.

Production of high quality sugarbeets requires that nitrogen be in adequate supply early in the growing season to develop an optimum canopy for photosynthesis, but decrease to deficiency levels approximately six weeks before harvest. If late planting shortens the growing season, nitrogen may not become limiting early enough to promote good quality. A general guide for spring applied nitrogen is to reduce the recommended nitrogen fertilizer rate by 10 pounds for each week that planting is delayed after May 20.

ADJUSTING NITROGEN RECOMMENDATIONS WHEN SAMPLING BELOW 2 FEET
There has been concern about accumulations of available nitrogen below the 2-foot depth. The original data that were gathered for calibration of the nitrogen test took into consideration available nitrogen to a depth of 5 feet. At that time sampling beyond 2 feet improved the recommendations somewhat but in most cases the extra effort to sample to a depth of 3 or 4 feet was not commonly justifiable.

Excessive applications of nitrogen, variable weather, and fluctuating crop yields and nutrient removal can result in a buildup of available nitrogen in the soil profile. When fields are tested for nitrogen each year and only the recommended amount of nitrogen is applied, an accumulation of nitrogen below 2 feet is unlikely. However, an advantage of sampling beyond 2 feet is that fields with large quantities of deep soil NO₃-N can be identified. Deeply located NO₃-N especially affects quality and yields of recoverable sugar. Fortunately, the incidence of fields high in NO₃-N has decreased during recent years.

If you suspect an accumulation of available nitrogen below 2 feet, have your fields tested to 4 feet. The following guidelines are then used to adjust nitrogen recommendations:

1. If the amount of NO₃-N in the 2 to 4-foot depth is less than 30 pounds NO₃-N per acre, no adjustment is made.
2. If the amount of NO₃-N in the 2 to 4-foot depth is more than 30 pounds NO₃-N per acre, the nitrogen recommendation should be reduced by 4 pounds for each 5-pound increment above 30 pounds found in the 2 to 4-foot depth. In other words, if there was 50 pounds of NO₃-N in the 2 to 4-foot depth the nitrogen recommendation would be reduced by 16 pounds (80 percent of 20 pounds)..

NITROGEN FERTILIZER USE GUIDELINES:

• 80-90 pounds of nitrogen per acre should be in the 0-2 foot depth soil profile to maximize early season crop growth, yield, and quality. This is regardless of the amount of residual soil nitrogen below 2 foot deep.
• About 30-40 pounds of nitrogen is the average amount found from 2 to 4 feet deep in the Red River Valley.
• Fields with less than 30 pounds of residual nitrogen below 2 feet deep may require additional added fertilizer nitrogen to maximize recoverable sugar per acre.
• About 60 pounds of nitrogen are mineralized from soil organic matter in an average year in the Red River Valley.
• Minn-Dak Farmers Cooperative and Southern Minnesota Beet Sugar Cooperative growers should consider applying 10 percent more nitrogen per acre because of payment scale differences with American Crystal Sugar Co.
• A good way to start effective nitrogen management is to calculate the nitrogen needed for a particular field according to past 3 to 5 year average yield. A split nitrogen application, 75 percent in the fall and 25 percent in the spring soon after planting based on planting date, plant population and other factors should minimize the loss of beet quality caused by over fertilization.
• Fall-applied nitrogen fertilizer is not recommended on sandy soils or soils with a high water table.
• Foliar nitrogen fertilizer applications to sugarbeet fields after June 30 have not generally increase hybrids.
• SET REALISTIC YIELDS GOALS: The present recommendations in Table 1 go to a maximum of 130 pounds of available soil plus fertilizer nitrogen. Many years of nitrogen management research at the University of Minnesota Experiment Station at Crookston and North Dakota State University indicates maximum recoverable sugar per acre, per ton, and greatest income per acre is realized when average soil plus fertilizer nitrogen is about 125-130 pounds per acre. Before fertilizing to in excess of 130 pounds per acre soil plus fertilizer nitrogen, contact your agriculturist, extension agent or university specialist.

P AND K RECOMMENDATIONS:
If your soil test is very low in phosphorus (less than10 pounds per acre) and potassium (less than 100), the NDSU recommendation will result in a small increase in the soil test level. If your P or K soil test is low, the recommendation replaces what is removed by the crop.

Phosphate and potash chemistry is different than that for nitrogen. The simple method of subtracting the soil test level from the amount needed for the crop does not work. The amounts of phosphate (P₂O₅) and potash (K₂O) needed to meet different goals are given in Table 1. All phosphorus and potash recommendations given in Table 1 are for broadcast application.

Since phosphorus and potassium move very little in the soil it is possible to "build up" or increase the available level of these nutrients in the soil with annual fertilizer applications. The application of approximately 10 pounds of P₂O₅ per acre will increase the phosphorus soil test level by 1. In other words, if your phosphorus soil test level is 12 and you prefer to operate at a test level of 25, the application of 130 pounds of P₂O₅ (285 pounds of 18-46-0) per acre thoroughly mixed in the top 6 inches of soil will raise the soil test level by 13. Likewise, the application of 5 pounds of K₂O per acre will increase the potassium soil test by 1.

PHOSPHORUS POTASSIUM APPLICATION:
Crops growing on soils that test very low in phosphorus and/or potassium depend heavily on applied fertilizer. On soils testing medium or above, the crop is much less dependent on applied fertilizer for its current needs. fertilizer is applied on these soils to replace nutrients removed by the crop and/or as a starter to get the crop off to a fast start, especially in cool, cloudy springs. On very low testing soils where the plants largely depend on fertilizer for their needs, the method of application will Influence the amount of fertilizer plants can recover. Broadcast fertilizer is thoroughly mixed with the soil and as a result some is positionally unavailable to plant roots. Band or drill row fertilizer is applied closer to the seed and can be recovered by the crop more efficiently. To convert the broadcast recommendations for phosphorus and potassium in Table 1 to band rates reduce the broadcast rate by 1/3.

MICRO AND SECONDARY NUTRIENTS:
Occasionally, growers have reported sugarbeet response to zinc (Zn). Before using zinc, obtain a soil test for this nutrient. Plant response to applied zinc with usually not occur, but is possible if the soil test level is less than 0.5 ppm zinc. Try applications of zinc as zinc sulfate or zinc In chelate form on a trial basis if a need for zinc is documented.

Responses to other micronutrients have not been reported or demonstrated. If questions arise about possible needs for manganese, copper, or iron, obtain a soil test for these nutrients.

Calcium deficiency may be observed in sugarbeets in Minnesota and North Dakota. However, it is apparently a physiological problem. Application of calcium containing fertilizers will not correct the problem. Yield losses due to this problem have not been documented.

FERTILIZER APPLICATION:
All NDSU phosphorus and potassium recommendations for sugarbeets are listed as amount to be broadcast. It is recommended that on very low and low-testing soils, phosphorus and potassium fertilizer be applied before the deepest tillage- operation for best incorporation. On medium-testing soils shallow incorporation is adequate.

USING STARTER FERTILIZERS:
Recent research in Minnesota and North Dakota indicates early season growth and/or yield responses to starter fertilizer occurs about 40 percent of the time. Significant responses are meet likely to occur when soils test very low to low in phosphorus or have low levels of available nitrogen In the top 6 inches of soil.

Sugarbeet seeds and seedlings are sensitive to fertilizer salts. Germination damage may occur if nitrogen or potassium fertilizer materials are placed in direct contact with seed.

In some areas it may not be possible to obtain straight phosphate fertilizer materials In sufficient quantities. In this case, use monoammonium phosphate (11-48-0) or 10-34-0 liquid as a starter fertilizer. Seed germination reduction from 5 or loss pounds of nitrogen per acre in contact with beet seed should be negligible and more than offset by the improved yields from the banded phosphorus application on very low-testing soils. Avoid in seed furrow starter applications with over 5-6 pounds per acre of nitrogen and potassium in contact with the seed.

On most soils, nitrogen fertilizer can be applied in either the fall or spring. However, we definitely do not recommend fall application of nitrogen on sandy soils, soils with a high water table, or soils subject to ponding. The best time to apply nitrogen fertilizer is as clove to the time the crop will need it as practical.

Although side dressing nitrogen on sugarbeets is generally not recommended, there may be times when it is not possible or practical to apply nitrogen before planting. When necessary, side dress nitrogen before sugarbeets have reached the eight to ten leaf stage. It is not recommended that nitrogen top dressing be done after July 1.

Helping You Put Knowledge To Work
NDSU Extension Service, North Dakota State University of Agriculture and Applied Science, and U.S. Department of Agriculture cooperating William H. Pietsch, Director, Fargo, North Dakota Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. We offer our programs and facilities to al person regardless of race, color, sex, religion, age, national origin, or handicap, and are an equal opportunity employer.

1988 Sugarbeet Research and Extension Reports. Volume 19, pages 69 - 72.

Questions/Comments