Managing Nitrogen Inputs For Sugarbeets
Robert Mullen, Ph.D.
Director of Agronomy
To say Dr. Robert Mullen is passionate about agriculture would be an understatement. He holds a Bachelor of Science degree in ag business from Cameron University, along with a Master of Science degree in plant and soil science and a Ph.D. in soil science from Oklahoma State University. In addition, Dr. Mullen has been published in a variety of scientific and trade journals. But it’s not just his academic accomplishments that make him unique. It’s his unwavering ability to take complex data and — in simple terms — explain how it impacts a farmer’s bottom line. Dr. Mullen delivers the kind of insightful observations that can lead to a more profitable business. As a leading agronomy expert, Dr. Mullen has a goal to further educate farmers on best management practices that improve their yields and maximize their return on investment.
The United States is one of the few sugar producing countries that grows significant volumes of both sugarbeets and sugarcane. Sugarbeets are responsible for producing 55-60 percent of the total sugar produced domestically (USDA-ERS). Sugarbeets accumulate significant amounts of biomass above and below ground translating to a significant demand for nitrogen. So how does one best manage nitrogen for sugarbeet production?
Managing nitrogen inputs for sugarbeets can be challenging. Too much nitrogen and sugar content of the beet decreases, too little nitrogen and beet yield is decreased. Both scenarios translate into lower overall sugar yield. Early season nitrogen is important for canopy closure and establishing leaf area, but ideally, as the crop nears the end of its life cycle, it should be exhibiting nitrogen deficiency. Therefore, nitrogen management must consider nitrogen rate, source, placement, and timing to maximize sugar yield.
Making Rate Decisions
The most reasonable place to start when discussing nitrogen management is rate. The four major states that produce sugarbeets provide the guidelines that will be discussed in this document (Idaho, Michigan, Minnesota, and North Dakota). There are other states that produce sugarbeets as well (California, Colorado, Montana, Nebraska, and Wyoming), but those recommendations will not be discussed. The greater range of recommended nitrogen rates in Idaho (typical of many western states) than in Midwestern States reflects a combination of the higher yields typically produced in this environment with irrigation and low organic-matter soils. Recent research on nitrogen rate response in Idaho is showing most current sugarbeet varieties produce greater yields with significantly lower nitrogen rates than varieties of a decade or more ago. Recommended nitrogen rates are being re-evaluated and lowered in many areas.
|State||Nitrogen rate range, lb/acre|
One feature of nitrogen rate recommendations of most states is the impact of the previous crop. Sugarbeets that follow grasses/high biomass non-legumes generally have higher recommended nitrogen rates. Conversely, sugarbeets that follow legumes/low biomass crops generally have lower recommended nitrogen rates. These lower reflected rates are not necessarily due to nitrogen contribution from the legume, but most likely due to decreased nitrogen immobilization because of lower carbon to nitrogen ratios and lower overall biomass associated with legume crops. Following legumes with sugarbeets may not be the most optimal crop rotation sequence because of potential late-summer nitrogen mineralization. Even though legumes may reduce fertilizer-nitrogen need, they may cause an increase in late season nitrogen availability because of decreased immobilization, resulting in decreased root sucrose content.7,8 The range of nitrogen rate reduction can be considerable, so see information for your geographic area to determine how much nitrogen you should apply.
The four states listed have nitrogen recommendations that are adjusted by soil nitrate level. The depth of nitrate testing does differ across these states. Minnesota3 and North Dakota1 have two different depths of sampling (2 foot and 4 foot), and different rate guidelines for each. Idaho4 recommends testing to a depth of 3 feet, but shallower samples can be taken (in 1-foot increments). As soil nitrate level increases, the rate of nitrogen recommended decreases. Since sugarbeets are so sensitive to nitrogen nutrition, spatial sampling may be a beneficial approach to determine nitrogen input need. Additionally, spatial management of other crops in rotation may help minimize areas of high nitrogen content.
Fall nitrogen applications in Minnesota/North Dakota may occur, but certain considerations should be made for those applications to minimize nitrate leaching. So-called “stale seedbed” applications are popular in some areas in which planting beds are formed in the fall, and nitrogen is broadcast before bedding or banded into the bed at that time. Fall nitrogen should not contain any nitrate, so avoid nitrogen sources like urea-ammonium nitrate (UAN) and ammonium nitrate. Soil temperatures should be below 50 degrees Fahrenheit to a depth of 4 inches prior to anhydrous ammonia applications. Subsurface-banded urea may be applied a week after the temperature threshold for anhydrous is reached, and broadcast urea (followed by incorporation) may be applied a week after banded applications6. Fall applications may consider inclusion of a nitrification inhibitor, but the use of an inhibitor should not be used to push application timings earlier than dictated by soil temperatures. If conditions for over-winter or early spring nitrogen losses are expected, fertilizer applications should be delayed until spring.
Spring nitrogen applications should be managed to minimize volatilization losses of nitrogen. Surface urea applications without incorporation (tillage or irrigation water) are not generally advised, especially in high residue production environments or soils with high pH (greater than seven)5. Surface urea-based nitrogen applications under these conditions can result in substantial volatilization losses.
Sugarbeet yield potential is established in the first weeks of growth and is driven by the rate of leaf expansion during this period. Sugarbeets may differ from other crops in that nitrogen concentration in the root zone during seedling development is a critical determinant of yield potential because of its effect on early leaf development. In most sugarbeet production areas, if fertilizer is broadcast, a minimum of about 60-90 pounds of available nitrogen per acre (soil plus fertilizer) is needed at planting to optimize early growth. If nitrogen is banded near the row (such as “2×2” placement), the minimum needed at planting may be as low as 30-60 pounds of nitrogen per acre.
Banding close to the row is the preferred nitrogen placement for sugarbeets. Sugarbeets have few if any lateral roots for the first six to eight weeks of growth, the critical period for yield-potential determination. Because nitrogen uptake is critical for early leaf development, banding as close to the row as is safe provides higher nutrient concentrations than broadcasting to better stimulate plant development. While sugarbeets are quite salt-tolerant once established, the small seedlings are sensitive, so nitrogen placement too close to the seed should be avoided. The so-called “2×2” placement should provide sufficient safety for practical fertilizer rates while optimizing nitrogen availability to developing seedlings.
In Michigan, in high residue settings, preplant or starter (2×2) applications are recommended2. The timing of nitrogen application is critical because late applications can result in decreased sugar content, so applications should be timed for preplant or prior to the four to six-leaf stage. In Minnesota, split applications of nitrogen in the spring are not recommend on clay/fine textured soils, and split applications for sandy/coarse textured soils should occur prior to July 1. These management strategies are promoted to decrease late-season nitrogen availability.
Five Take Home Points
- Utilize a realistic yield goal to determine rate, or employ justified rates of nitrogen to maximize sugar yield (including the use of soil testing and consideration for the previous crop)
- Time applications early to decrease late season nitrogen availability
- In areas where fall applications may be used, avoid use of nitrate containing fertilizers
- Manage urea applications to minimize volatilization losses
- Spatial soil sampling techniques and spatial nitrogen management can be beneficial to minimize areas that are nitrogen rich
For more information from the states referenced in this article, visit the following links: