Sugarbeet fertilizer guidelines

Nitrogen

Nitrogen is the single most important nutrient for optimum sugarbeet production.  Nitrogen status of the plant affects early growth or time to full canopy closure and the quality of the sugarbeet at harvest.  Optimum nitrogen management promotes vigorous early season plant growth reducing the number of days to canopy closure which allows the sugarbeet to utilize the sunlight’s energy more efficiently to make sucrose.  Excess N at or near the end of the growing season reduces sugarbeet quality by reducing sucrose concentration and increasing impurity concentration.  Research has indicated that the greatest sugarbeet quality occurs when the plants undergo N deficiencies late in the growing season starting about six weeks prior to harvest.  However, the development of severe N deficiencies too early in the growing season, while enhancing quality, will reduce sugarbeet root yield.  The Minnesota soils, where most of the sugarbeets are grown, can mineralize sufficient N from their organic matter to reduce the severity of N deficiency later in the growing season.  Therefore, a good fertility program needs only to provide N during the early and mid-parts of the growing season.

Soil testing for nitrate

The amount of nitrogen fertilizer application to a sugarbeet crop should be based on a total N recommendation minus the nitrate-N from a soil test.  The time of year at which the sample is taken is important.  A soil sample for soil nitrate-N should be taken when the soil temperature at six inches depth have consistently dropped below 50 degrees F.  Earlier sampling times will result in an inaccurate soil test value, see Figure 1.  The depth to which to take the required soil test depends on the previous history of nitrogen management.  It is recommended that a soil sample to a depth of four feet be taken if little knowledge exists on levels of nitrate-N below two feet.  The recommendation based on a sample taken to four feet is 100 pounds N per acre (Table 1).  This recommendation includes the amount of nitrate-N in the soil sample and the amount added as fertilizer.  If for some reason you can only sample to a depth of two feet, then the recommendation is 80 pounds N per acre.  In some cases where previous management and soil conditions occur that would cause a large amount of residual nitrate-N to be in the soil, a sample to a depth of six feet may be needed.  In all cases, it is suggested that a minimum of 65 pounds N per acre in the zero to two foot depth should be present no matter how much nitrate-N occurs in the two to four foot depth.  Research has indicated that the soil samples should be taken from areas of 20 acres in size or less that are similar in landscape, soil type, or previous management.

Nitrogen Sources

The summary of several research trials indicate all N sources will perform similarly if applied appropriately to minimize losses. For environmental and N loss concerns, fall applications of nitrate forms of fertilizers such as urea ammonium nitrate solution (UAN) or ammonium nitrate are strongly discouraged.  Anhydrous ammonia and urea N sources can be used either as preplant applications in the spring or the previous fall after soil temperatures at the six inch depth fall below 50 degrees F.

Split Applications of Nitrogen

Split applications of N fertilizer may be wise for sugar beets grown on sandy soils.  The split applications should be scheduled so the last application is done before July 1 to minimize the possible reduction in root quality at harvest.  Research conducted in the 1980's and 1990's on heavier textured soil indicate that split applications did not perform better than a preplant application and actually decreased root quality in recent trials conducted in the Red River Valley, Table 2.

Previous Crop and Rotation Management

The above recommendations must be modified based on crop rotation and previous input management.  The soil nitrate test is not accurate in situations where the previous crop is a legume such as alfalfa or manure applications have been made.  It is strongly recommended not to grow sugarbeets following alfalfa or where manure has been applied the previous year because of the increase nitrogen mineralized from organic N sources during the growing season.  Research with sugarbeet growth following alfalfa and manure application indicates that while root yield was not affected, the use of nitrogen fertilizer reduced sucrose concentrations and recoverable sucrose yields. 

If a grower must use manure in the rotation, then it must be managed to take credit for the nitrogen mineralization that occurs from the manure.  For more information on manure management, consult University of Minnesota Extension publication AG-FO-03553, Manure Management in Minnesota.  This publication discusses nitrogen credits from different types and application methods of manure.  The grower also much recognize the variability in the rate of nitrogen mineralization from the manure.

In the past it has been recommended not to grow sugarbeet after soybean but recent research in Southern Minnesota and Northwestern Minnesota indicate that if the diseases such as rhizotonia can be controlled, a good sugarbeet crop can be grown.  Research from the Southern Minnesota area, Table 3, indicates in two of three years growing sugarbeet after corn resulted in the least extractable sucrose per acre while sugarbeet grown after spring wheat resulted in the greatest extractable sucrose.  Intermediate results were found when growing sugarbeet after soybean.  The previous crop in this research did not affect the optimum N application. 

Phosphorous

Phosphorus is used by the plant for energy compounds.  Phosphorus has been documented to increase root yields in soils that are low in phosphorus while not affecting quality.  Since phosphorus is immobile, Guidelines are based on a soil sample from the surface 6 to 8 inches (Table 4).  The phosphorus soil test does not measure the chemical form utilized by the plant as is the case with the nitrate test.  The P soil test is only an index that has been correlated to the crop response to P fertilizers in field trials.  If the pH of the soil is less than 7.4 then you should use the Bray P1 soil test.  For soils that have a pH of 7.4 and greater the use of the Olsen P soil test is suggested.

Phosphorous Fertilizer Placement

Recent research conducted in Northwest Minnesota indicates that the use of a starter placement (pop-up) of fertilizer phosphorus with the sugarbeet seed is more efficient than a broadcast application.  Phosphate application rates of 3 gallons of 10-34-0 (12 lbs phosphate per acre) placed on the seed at planting produced similar root yields as a broadcast application of 45 to 60 pounds phosphate per acre, Figure 2.

Greenhouse work in Minnesota and Nebraska indicate that early sugarbeet growth is enhanced with starter placement of phosphorus, but there is a difference in the placement of the starter band.  Placement with the seed or two inches below the seed was superior to the more conventional placement of two inches to the side and two inches below the seed.

If you choose to use the seed placement option, there are cautions on the amount which can be applied.  Applying greater than five pounds per acre of N + K2O in contact with the seed can reduce plant stand emergence.  The amount of P in contact with the seed has not been detrimental to plant stands.  The occurrence of stand reduction increases with decreasing soil moisture condition at the time of planting. 

Potassium

At this time, the use of a starter fertilizer with potassium is not recommended because there is little research on the effect these sources have on sugarbeet growth and only a small amount of the sugarbeet growing areas need potassium fertilization.  Potassium is essential to sugarbeet production and is not mobile in the soil.  The soil test is based on an ammonium acetate extraction on a surface six to eight -inch deep soil sample, Table 6.  If the soil test is in the responsive range, placement can be similar to phosphorus except extreme caution should be exercised when placing in contact with the seed.  Potassium is not a large concern in Southern Minnesota because the majority of the soils where sugarbeet is grown are natively high in potassium.

There has been no documented yield or quality responses to other nutrients such as sulfur, zinc, magnesium, calcium, boron, or sodium in Southern Minnesota sugarbeet growing area.

Work from North Dakota State and the University of Minnesota’s Northwest Research and Outreach Center indicate that nitrogen credits should be given for nitrogen in the sugarbeet tops for crops such as small grains and corn grown after the sugarbeet crop in rotation.  If sugarbeet top growth is lush and green, the credit could be as great as 70 pounds N per acre.  Research in southern Minnesota has not confirmed the N credit of sugarbeet tops for corn production following sugarbeet in the rotation. 

If you are growing corn following sugarbeet in the rotation, you should consider using a starter application of 40 pounds phosphate per acre.  If the EDTA zinc soil test is low, also include two pounds of zinc in the starter.