Fertilizing Sugarbeet

SF-714 (Revised), October 1992
Reviewed and Reprinted January 1993

Allan Cattanach, Sugarbeet Specialist, NDSU & U of MN Extension Services
W. C. Dahnke, Soil Testing and Dept. of Soil Science
Carl Fanning, Soils Specialist, NDSU Extension Service

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.

Sugarbeet 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 using recognized procedures and interpretations. Because of soil NO3-N mobility, test each year for nitrogen 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 extraction of sucrose by the processor. Production of high quality sugarbeet 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. Too much nitrogen 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 and adequate plant populations, weed control, timeliness of operations, and disease and insect control will all improve recoverable sugar yield. A good method for selecting a yield goal is to aim for �3 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 chance of having low sugar and high impurities greatly increases. When growing season rainfall is sufficient for yields above 22 tons, increased mineralization of nitrogen from organic matter should occur to provide nitrogen for these higher yields.

Fertilizer Recommendations

Table 1 shows the amount of soil NO3-N in the top 2 feet of soil, plus added nitrogen fertilizer needed to meet the requirements for various sugarbeet yield goals. These data are based on nitrate-nitrogen levels in soil samples taken between September 15 and April 1. If soil samples are taken between July 1 and September 15 subtract 0.5 pound of nitrogen from the recommendation for each day that the soil was sampled prior to September 15. These adjustments are automatically included in recommendations received from the North Dakota State University Soil Testing Laboratory.

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 residual 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 sugarbeet 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. Deep soil NO3-N especially affects quality and yields of recoverable sugar. Fortunately, the incidence of fields high in NO3-N has decreased in recent years.

If you suspect an accumulation of available nitrogen below 2 feet, have your fields tested to 4 feet. The following guidelines are 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 were 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).

When to Soil Sample to a Four Foot Depth

1. When your crop quality is consistently lower than the piler or factory average.
2. When buying or renting land with unknown crop or fertilizer history.
3. Where previous crop yields were less or much less than normal.
4. On fallow land, especially after a heavy rainfall fallow season.
5. Where manure is used for fertilizer.

Nitrogen Fertilizer Use Guidelines

• 80-90 lbs of residual soil plus added fertilizer 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 feet deep.
• 10 to 15 lbs of nitrogen per acre in the top 6 inches of soil should be adequate to establish the crop.
• About 30-40 lbs of nitrogen is the average amount found from 2-4 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 lbs of nitrogen mineralizes from soil organic matter in an average year in the Red River Valley.
• Minn-Dak Farmers Cooperative growers should consider applying 10 percent more nitrogen per acre than is shown in Table 1 because of payment scale differences with American Crystal Sugar Co. The NDSU Soil Testing Lab will automatically make this adjustment when providing recommendations.
• Cattle and swine manure will supply 5 lbs of nitrogen per ton in year of application. Poultry manure will supply 15 lbs of nitrogen per ton. Know how many tons were applied.
• A good way to start effective nitrogen management is to calculate the nitrogen needed for a particular field according to the past three- to five-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 due to 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 increased yields. They may reduce crop quality.
• Set Realistic Yield 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 available 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. Most growers ask for a yield goal of 18 or 20 tons per acre.

P & K Recommendations

If your soil test is low in phosphorus (less than 10 ppm), and potassium (less than 80), the NDSU recommendation will result in a small increase in the soil test level. If your P or K soil test is medium, 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 20 pounds of P2O5 per acre will increase the phosphorus soil test level by 1. In other words, if your phosphorus soil test level is 5 and you prefer to operate at a test level of 12, the application of 140 pounds of P2O5 (305 pounds of 18-46-O) per acre thoroughly mixed in the top 6 inches of soil will raise the soil test level by 7. Likewise, the application of 10 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 on very low testing fields.

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 will 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 indicated.

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

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

Fertilizer Application

All NDSU phosphorus and potassium recommendations for sugarbeet 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 most likely to occur when soils test very low to low in phosphorous or have low levels of available nitrogen in the top 6 inches of soil.

Sugarbeet seed and seedlings are sensitive to fertilizer salts. Germination or emergence 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 less 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 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 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 before seeding or as close to the time the crop will need it as practical.

Although side-dressing nitrogen on sugarbeet 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 sugarbeet have reached the eight- to 10-leaf stage. It is not recommended that nitrogen topdressing be done after July 1.

Fertilizers and Water Quality

Nitrate nitrogen (NO3-N) is water soluble. It may move with soil water into tile lines or ground water. Understanding nitrogen movement in soil is vital to protect water quality. Nitrogen fertilizer should never be applied without following a nitrogen soil test recommendation. Fertilizer nitrogen should be carefully managed throughout all crops in the rotation. On coarse (sandy) textured soils avoid fall application of nitrogen fertilizer and/or use split applications of nitrogen. Reduce soil movement to lakes and streams by erosion control practices. Avoid excess N applications by setting realistic yield goals. Give proper credit to manure applications, N supplied by legumes or in previous crop residues when applying fertilizer nitrogen. Manage irrigation systems to minimize excess applications of water.

Table 1. Nitrogen, Phosphate and Potash Requirements for Sugarbeet.

				     Soil Test Phosphorus, ppm	     
				-----------------------------------
		 Soil N plus		VL    L	    M	  H	VH   
  Yield goal*	 fertilizer	Bray-I	0-5  6-10 11-15 16-20	21+  
Sucrose	  Beets	 N required	Olsen	0-3  4-7   8-11 12-15	16+ 
-------------------------------------------------------------------
lb/a	  ton/a	  lb/acre-2'	     --------- lb P2O5/acre -------
5280	   16	     95			65    45    30    10	 0 
5610	   17	    100			70    50    30    10	 0 
5940	   18	    110			70    50    30    10	 0 
6270	   19	    115			75    55    35    10	 0 
6600	   20	    120			80    55    35    10	 0  
7260	   22	    130			90    65    40    15	 0  
-------------------------------------------------------------------


				       Soil Test Potassium, ppm
				    ------------------------------------
		 Soil N plus	       VL     L      M	H      VH 
  Yield goal*	 fertilizer   Bray-I  0-40  41-80  81-120  121-160  161+ 
Sucrose	  Beets	 N required   Olsen	
-------------------------------------------------------------------------
lb/a	  ton/a	  lb/acre-2'	     ----------- lb K2O/acre -----------
5280	   16	     95		       90     65     40	     15	     0 
5610	   17	    100		      100     70     45	     15	     0 
5940	   18	    110		      100     70     45	     15	     0 
6270	   19	    115		      110     80     50	     15	     0 
6600	   20	    120		      110     80     50	     15	     0 
7260	   22	    130		      125     90     55	     20	     0 
-------------------------------------------------------------------------
*Sucrose lb/a assumes 18.0% sugar content with 1.5% sugar loss 
to molasses.

Nitrogen recommendation  = 6 YG - STN + SDA - PCC    
N for Minn-Dak sugarbeet = 7 YG - STN + SDA - PCC 
Bray-I P recommendation  = (4.38-0.22 STP)YG  
Olsen P recommendation   = (4.38-0.27 STP)YG  
Potassium recommendation = (6.350-0.042 STK)YG 

The abbreviations used in the equations are as follows:
YG = yield goal		    STK = soil test potassium
STN = soil test nitrogen    SDA = sampling date adjustment
STP = soil test phosphorus  PCC = previous crop credit

SF-714 (Revised), October 1992
Reviewed and Reprinted January 1993