Sugarbeet fertilizer recommendations

Nitrogen is the most important nutrient when planning a fertilizer program for sugarbeet production.  Nitrogen status of the plant affects early growth and the quality of the sugarbeet at harvest. Early canopy closure allows the sugarbeet to make better use of sunlight and produce more sugar.  Excess nitrogen at or near the end of the growing season reduces sugarbeet quality by reducing sucrose concentration. The highest quality sugarbeet will have nitrogen deficiency late in the growing season (about 6 weeks before harvest).

Adjust the amount of suggested nitrogen fertilizer for the amount of NO₃^--N measured in the soil profile to a depth of four feet. The nitrogen fertilizer guideline will depend on the growing location. For the Minn-Dak and American Crystal growing areas, you need a 130 lbs per acre as soil test NO₃^--N in the surface 4 feet plus fertilizer N. If you can't get a four foot sample and you suspect there are small amounts of NO₃^--N at two to four feet, use a two foot depth. The total N would be 110 lb per acre soil test NO₃^--N plus fertilizer N. In the Southern Minnesota Beet Sugar Cooperative growing area, you need 100 lbs per acre at four feet and 80 lbs per acre for a 2 foot soil test.

Field research shows that the source of the fertilizer doesn't matter as long as it's applied in a way that will reduce loss. However, we discourage growers from using liquid nitrogen (28-0-0) and ammonium nitrate (33-0-0) in the fall. Split applications of nitrogen may be wise for sugarbeets grown on sandy soils. Make sure your last application takes place before July 1. For soils that are not sandy, there's no need to split apply. In fact, split applications on non-sandy soils have shown to cause a decrease in the quality of the crop.

Soil testing for nitrate

Base the amount of fertilizer you apply on a total N recommendation minus the nitrate-N from the soil test. For the depth of sampling, refer to previous history of nitrogen management and the policy of the Sugar Cooperative. Take a sample at four feet if you're not sure how much nitrate-N there is below two feet. The recommendation based on a sample taken to 4 feet is 130 pounds N per acre. 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 2 feet, then the recommendation is 100 pounds N per acre. In some cases, if your previous management and soil conditions have caused a lot of residual nitrate-N in the soil, you'll need to sample at six feet. In all cases, have a sample of 65 pounds N per acre at the zero to two foot depth, no matter how much nitrate-N is at two to four feet.

Previous crop and rotation management

Use the above recommendations, but modify based on crop rotation and previous management. The soil nitrate test is not accurate in situations where the previous crop is a legume, like soybean or alfalfa, or where you've applied manure. In these cases, there will be a higher level of nitrogen mineralized from organic N sources during the growing season. Research data and Sugar Cooperative Grower records show reduced sugarbeet root yield and quality when grown after soybean. With sugarbeet after alfalfa or manure, root yield is not affected, but nitrogen fertilizer reduced sucrose concentrations and recoverable sucrose yields.

The sugarbeet plant uses phosphorus for energy compounds. Phosphorus increases root yields in soils that are low in phosphorus while not affecting quality. Since phosphorus is immobile in the soil, recommendations are based on a soil sample to a depth of 6 to 8 inches. 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 correlated to the crop response to P fertilizers in field trials.

The availability index (soil test) used for recommendations is dependent on the soil's pH. If the pH is less than 7.4, use a Bray P1 soil test. When the pH is 7.4 or greater, use the Olsen P soil test. At this time, the University of Minnesota and North Dakota State University do not support the Mehlich III soil test. The recommendations suggested in Table 1 are based on broadcast applications of P fertilizer.

P fertilizer placement

Recent research at the University of Minnesota's Northwest Research and Outreach Center indicates that the use of a starter placement of fertilizer phosphorus with the sugarbeet seed is more efficient than a broadcast application. Phosphate application rates can be reduced up to one-half of the broadcast application rates and still produce similar yields.

Greenhouse work in Minnesota and Nebraska indicates 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 2 inches to the side and 2 inches below the seed. If you choose to use the seed placement option, be cautious with how much you apply. Applying greater than 5 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.

The source of starter fertilizer is not a factor in getting a yield response. Dry and liquid starter fertilizer sources will perform similarly. The only difference is the amount that can be applied in contact with the sugarbeet seed. Common phosphorus fertilizer sources that can be used and their maximum recommended application amounts are listed in Table 1.

At this time, we do not recommend using a starter fertilizer with potassium. 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 6- to 8-inch deep soil sample. Potash fertilizer can have a negative effect on germination if placed on or too close to the seed. Therefore, broadcast applications of potash are suggested.

There have been no documented yield or quality responses to other nutrients such as sulfur, zinc, magnesium, calcium, boron, or sodium in the Minnesota and North Dakota sugarbeet growing areas.

Cautions

Those who choose to place fertilizer with the seed should use caution. Applying more than 5 lb. per acre of N + K₂O in contact with the seed can reduce emergence and subsequent stands. The chance of reduced stands increases as soil moisture content decreases. The use of 10-34-0 at rates less than 4 gallons per acre in 22 inch rows has not been harmful.

For small grains and corn after sugarbeet in rotation, apply a nitrogen credit to account for the sugarbeet top. If sugarbeet top growth is lush and green, the credit could be as great as 70 pounds N per acre.

If you are growing corn following sugarbeet, consider using a starter application of 40 pounds phosphate per acre. If the EDTA zinc soil test is low, also include 2 pounds of zinc in the starter.