Sugarbeet Agronomy 101

Sugarbeets play a significant role in the irrigated agriculture picture of the Lower Yellowstone River. Growing high yielding, good quality beets is the yearly goal of many Montana irrigators. That being the case, the following information and facts might prove valuable to beet growers.

A Few Quick Facts

• Soil moisture levels should be maintained above 65% available moisture.
• Sugarbeets develop in an active root zone of 3.3' with 70% of the water drawn from the top 2' of this root zone.
• Sugarbeets are most sensitive to moisture shortages and salinity in the early growth stages (germination and seedling).
• Over the peak 30 day growing period (July 21-Aug.20), maximum water use is 0.24"/day. Maximum use during a 10-day peak will reach 0.28"/day.
• A dark green color of the beet leaves is an obvious sign of stress. At his point, irrigation should begin immediately.
• Under-irrigating will cause stress and reduce yield, while over-irrigating near harvest reduces sugar content.
• The average yield for sugarbeets is 19-22 tons/acre. Top yields can range from 26-30 tons/acre.

Water Use and the Sugarbeet Root Zone

Sugar beets require 22-28" of water during the growing season. Considering that sugarbeets are considered a moderately long-season crop, averaging more than 120 days of vegetative growth, this amount of water equates to 0.15-0.18 inches per day, on the average. During the hottest days of the summer, when the root system is nearly fully developed, a beet crop will use as much as 0.28 inches of water per day. That equates to an irrigation strategy requiring water about every 14 days. How do we get a value of 14 days? Assume a soil can hold 2.5" of available moisture per foot, and the active root zone is 3.3 feet. That means the soil just after irrigation can supply 8.25" of water (2.5"/foot x 3.3' root zone). But, the recommended maintenance soil moisture level is 65% of available moisture, which leaves 2.9 inches of water for the plant. If we use that value and divide by 0.28"/day, the net result for this specific soil is about 10 days. The bottom line is this: maximizing yield and sugar production requires fairly frequent irrigation.

Disease

Studies have shown that previous crops which contribute a lot of crop residue to the soil, such as wheat or sorghum, will result in higher levels of disease in the subsequent sugarbeet crop compared to beets grown following crops such as alfalfa or sunflowers. Crops preferred in a short term rotation with sugarbeets include beans, sweet clover, corn, grains, peas, potatoes, and if you are inclined to try something different, tomatoes. Alfalfa is a suitable crop in a long term rotation with sugarbeets. The other factor that seems to play a significant role with respect to diseases in sugarbeets is the occurrence of activities that wound the roots. This makes the roots more susceptible to attacks by bacteria and fungi.

Nutrient Requirements

Adequate top and root growth require large amounts of N, but if storage roots are to be high in sucrose concentration, the plants must be N deficient for 4 to 8 weeks before harvest. Studies have reported that if the nitrate content in the sugarbeet is above 1000 ppm within 6 weeks of harvest, the sugar content will be decreased. Too much N results in high root yields accompanied by low sucrose content and high concentrations of impurities, particularly sodium and amino-N. High concentrations of impurities reduce the percentage of extractable sucrose. Too little N results in high sucrose yield and good quality, at the expense of root yield.

Reducing the amount of applied N does not decrease sucrose yield or gross income of early harvested sugarbeets. A reduced N rate is appropriate for early contracted sugar beets. A rate of N above the recommended rate does not boost sucrose yield or gross income of sugar beets harvested late in the season.

So, one of the best strategies for nitrogen fertilization of sugarbeets is to determine a reasonable yield goal, manage your water to achieve 10% more than that yield goal, and manage your nitrogen fertilizer to achieve the yield goal or slightly less. That way, you'll have enough nitrogen to supply the crop but not so much that it carries over late into the season.

Spacing and Yield

Sugarbeet planting spacing is pretty well established by tradition, previous experience, and existing equipment. However, it doesn't hurt to look around once in a while. The following table shows the results of a study conducted at Malheur Experiment Station in Ontario, OR. Beets were grown in 11" and 22" row spacings with a variety of plant spacings within the rows. The results showed increased yield, sugar content, and extraction for the beets grown in 11" rows over those grown in 22" rows. It follows that growing sugarbeets on narrower rows has the potential to increase total sugar production. In addition to potentially higher yields, narrow-row sugarbeets form a canopy over the soil earlier in the season, perhaps making them more competitive with weeds than sugarbeets in 22" rows.

Other Resources
http://www.agric.gov.ab.ca/irrigate/sugarbeet.html