AUGUST 1976

FERTILIZING SUGARBEETS

Profitable sugar beet production depends largely upon a high tonnage crop containing a high percentage of sucrose. To accomplish this growth limiting factors including soil fertility must be handled effectively.

Sugar beets are unique in their requirements for nitrogen. Too little nitrogen results in premature yellowing and reduced yields, while too much nitrogen leads to a reduced sucrose percent accompanied by an increase in impurities. To prevents 'too little' or 'too much' nitrogen situation, which can result from selecting the wrong field or applying inadequate or excessive nitrogen fertilizer, it is very important to determine the amount of nitrate-nitrogen already present in the soil. The amount of nitrate-nitrogen in the soil can be determined by having y our soil tested at a reputable laboratory that uses recognized procedures and interpretations. Considering the mobility of the soil nitrate-nitrogen, test soils each year for nitrogen recommendations. Test every three or four years for phosphorus and potassium.

SOIL TEST RATINGS
Soil testing is used to obtain information needed to evaluate the fertility level of the soil on which the beets are to be grown. On the basis of soil test data, the soil is ranked very low (VL) low (L), medium (M), high (11), or very high (VH) for each plant nutrient for which a test is made.

Nitrogen: The assigned soil test ratings for nitrogen are shown in Table 1. These ratings are based on a combination of the soil test. which evaluates the fertility level at the time of sampling, and root and sugar yield goals. Yield goals must be considered because the plant-available nitrogen needed increases greatly as yields increase. To cite an example of the change in rating in relation to yield goals. consider that (50 pounds of nitrate-nitrogen was present to a depth of two feet at the time of sampling. It the yield goal is I2 tons of beets per acre (3600 pounds of sugar per acre) the soil test rating is medium, (~1) but if the yield goal is 26 tons per acre ( 7800 pounds of sugar per acre) the rating is very low (VL).

Phosphorus and Potassium. The assigned soil fertility ratings for phosphorus and potassium are shown in Table 2. These ratings are based 011 the soil test which evaluates the fertility levels of P a1ldK at the time of sampling. Although the phosphorus and potassium required for the crop also increases as yields increase, test ratings for these nutrients are not changed with increasing yield goals.

YIELD GOALS
When setting a sugar beet yield goal for which fertilizer recommendations are requested, remember that sugar is the product sought. Over-fertilization, particularly with nitrogen, can result in poor quality beets, and reduced net returns. Thus, in setting yield goals, improvement of management factors such as evenly spaced and adequate plant populations, weed control, timeliness of operations (especially early planting). disease and insect control, and the like, must all be improved along with increased fertilizer use. Also, other yield influencing factors, such as the expected or potential climatic conditions. stored soil moisture levels, and the production capacity of the soil must also be considered in estimating yield goals. A good starting point is to take the highest yield that has been produced on a particular field and make adjustments up or down. Usually the goals not11d be within three tons of the highest yield produced on your farm.

FERTILIZER RECOMMENDATIONS
Nitrogen: Table 3 shows the amount of soil NO₃-N, as determined by NDSU soil tests, plus N fertilizer needed in the top two feet of soil to meet the nitrogen requirements of various yield goals for sugar beets. These data are based on soil NO₃- N levels as determined through the analysis of samples taken between September 1 and April 1. For soil samples taken after April 1, increase these figures by 20 pounds before fertilizer needs are determined.

To determine fertilizer nitrogen requirements, field the amount of soil plus N fertilizer needed for your yield goal in Table 3 and subtract the soil test level of NO₃-N.

As an example:

Your NDSU soil test shows that there are 50 pounds of NO₃-N present till the soil to two feet. Your yield goal is 16 tons per acre (4800 pounds of sugar per acre). So you should apply 80 pounds actual nitrogen (N) per acre. (This is the difference between 130 pounds taken from Table 3 and 50, pounds from the soil test.)

Production of high quality sugar beets requires that nitrogen be in adequate supply early in the growing season, but approaches deficiency levels approximately six weeks before harvest. Thus, if late planting shortens the growing season, you should also reduce nitrogen fertilizer rates. A general guide is to reduce recommended fertilizer rates by 10 pounds of N for each week planting is delayed after May 20.

Phosphate and Potash: Because of the nature of phosphate and potash soil chemistry, 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 yield goals are given in Table 4.

As an example:

If the yield goal for sugar beets is 16 tons (4800 pounds of sugar per acre) and the phosphorus fertility level is medium (M) and the potassium fertility level is very high (VH), the fertilizer recommendation would be 35 pounds per acre of P₂O₅ and 110 K₂O

Micronutrients: During the past few years there have been reports of responses to zinc (Zn) on sugar beets. Before using Zn, obtain a soil test for this nutrient. If results of such a test show a soil fertility level of less than 0.5 ppm Zn, try applications of 10 to 15 pounds per acre actual Zn as Zinc sulfate or 2 to 3 pounds per acre actual Zn inch late form on a trial basis.

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.

NITROGEN AND QUALITY
Sugar beet quality involves two different concepts. The first is the percent sucrose in the root. The second is the level of impurities in the roots which affect extraction of sugar by the processor. Production of high quality sugar beets is especially important to the grower being paid on the individual sugar content of his beets.

Nitrogen fertilizer use normally increases yield of roots and sugar. It also increases impurities and decreases the percent sucrose in the root. Use soil test information to select fields with nitrogen levels suited to expected yields or to fertilize to meet expected yield goals. Excessive use of nitrogen fertilizer usually lowers beet quality significantly.

FERTILIZER APPLICATION
All NDSU phosphorus recommendations for sugarbeets are in terms of the amount to be broadcast. It is recommended that on very low. Low and medium testing soils that the phosphorus fertilizer be applied before the deepest tillage operation. On soils testing high and very high, shallow incorporation is adequate.

Sugar beet seeds and seedlings are sensitive to fertilizer salts and germination damage may occur if nitrogen or potash fertilizer materials are placed in contact with the seed.

Phosphate fertilizers have a low salt index and can be placed safely in contact with the seed. When phosphate is banded with or near the seed, its availability and efficiency is usually improved. especially for early season growth. Use of banded phosphate fertilizer at one-half the rate recommended in Table 4 can be important on soils testing very low and low in phosphorus.

In some areas it may not be possible to obtain straight phosphate materials in sufficient quantities to meet your phosphate fertilizer needs. In this case, you may use monoammonium phosphate (1148-0) as a starter fertilizer at rates up to 50 pounds of material per acre. The small amount of germination damage that may result from the seed contact with the nitrogen will generally be more than offset by the improved yields resulting from the banded application of the phosphorus.

On most soils nitrogen fertilizer can be applied either in the fall or spring except it is definitely not recommended to fall apply nitrogen on coarse textured soils, soils with a high water table, or on soil subject to ponding. For most efficient use of nitrogen fertilizer it is recommended that it be applied as close to the time the crop will need it as practical. Although side dressing nitrogen on sugar beets is generally not recommended there may be times when it is not possible or practical to apply nitrogen before planting. When this is the case side dress nitrogen before the sugar beets have reached of the four or six leaf stage. When side dressing sugar beets, reduce the recommended rate by 10 pounds of nitrogen for each week beyond May 20.

SPECIAL NOTE: When taking soil samples, take special care to assure that the samples will represent the field being tested. Soil samples should not be stored moist, but air dried as soon as possible. For complete information on soil sampling please refer to NDSU Extension Circular S-F 336 Rev. "Soil Test for Profit - The Key to More Efficient Fertilization" available from your County Extension Agent.

NOTE: Foliar application of fertilizers or unregistered chemicals is generally not recommended and may be detrimental to production of quality sugar beets. For more information on soil testing and fertilizer use contact NDSU soils specialists, your county extension agent, factory fieldmen or fertilizer dealer.

1977 Sugarbeet Research and Extension Reports. Volume 8, pages 102 - 105.

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