Nitrogen management for beets
Nitrogen rates and timing are critical for optimum yield, quality and profitability for sugarbeets.
Nitrogen is typically the most important nutrient in sugarbeet production. If an inadequate amount of nitrogen is applied, beet yields will suffer. Too much nitrogen can significantly reduce beet quality. The goal in nitrogen management is to achieve the optimum economic recoverable sugar per acre based on each sugar company’s payment plan.
No other nutrient related to sugarbeet production has been as widely researched as nitrogen. In most sugarbeet growing areas, it is generally agreed that optimum beet production requires between 6 to 8 pounds of nitrogen per ton. This nitrogen is supplied by residual nitrate in the soil, mineralization of organic matter, and applied fertilizers. How much you get from each source has always been the question and is field specific.
Universities have been active in developing soil nitrate testing procedures that do a good job of predicting nitrogen availability in some beet producing areas. Nitrate testing is highly encouraged in these areas. In Michigan, soil nitrate testing has been helpful but not as reliable as other beet producing areas. High precipitation events can change nitrate levels from fall to spring and also during the growing season. General applied nitrogen recommendations for Michigan range from 90 to 120 pounds if following dry beans or soybeans and 125 to 150 pounds if following a high residue crop such as corn or wheat.
Early season nitrogen availability is very important to promote early growth of leaf canopy. Light interception by the leaves is directly related to sucrose production. For this reason we should strive to have complete canopy by June 20, the longest day of the year. By August, if early Nitrogen has been applied at the appropriate level, sugarbeets will have taken up most of Nitrogen required. A total of 80 to 90 percent of that N will be in the shoot. This Nitrogen can be remobilized from the tops to the roots for supplying plant needs.
The effect of excess nitrogen in late summer can be very detrimental to quality for several reasons. The crop will continue to take up N leaving less mobilized from the old leaves. These old leaves will be retained longer along with producing new, large, late-formed leaves. These factors combined will give huge tops at harvest. This energy to produce and retain leaves has been diverted from sucrose production and storage.
In many crop species there is a direct relationship between nitrogen content of the crop and yield. In sugarbeets, above optimum levels, no direct relationship exists between increased N uptake and sucrose yield. This is because increased leaf area is not proportional to light interception. A leaf area index of three to four will capture most of the available sunlight. Increasing the canopy beyond that point will not significantly collect more. By late season, a moderate canopy can intercept most of the available solar radiation. Excess nitrogen has also a negative effect on ratio of tops to roots. Late N also causes nitrogenous impurities that impede sucrose extraction. Increasing nitrogen rates above proven optimum levels can be very costly to sugarbeet producers.
In summary, the goals of nitrogen management are to plan fertilizer applications that will promote early season leaf growth. Supply enough nitrogen to maintain a canopy through the season while minimizing excess late canopy growth. Importantly, avoid late season excess N-Compounds which depress root quality.