When grown for sugar production, in the vegetative or first stage of growth, sugarbeets will keep growing almost indefinitely if environmental conditions permit them to do so. That is why sugarbeet growing areas, which have longer growing seasons, also have higher root yields. Sugarbeet quality in any growing area is achieved by manipulating nitrogen management to see that fertilizer applications match crop growth requirements.

Nitrogen promotes plant growth in sugarbeets and is vital for good crop production. However, with sugarbeets, the timing of nitrogen availability to the crop is critical. If nitrogen is inadequate in the early stages of crop growth, yields can be seriously reduced. If nitrogen is excessive in the later growth stages, sugar content and beet quality will be decreased. In sugarbeet production both the timing of application and the quantity of nitrogen used are important. Research results over a wide range of environmental conditions and across a number of years have shown that in the TASCO growing area, seven to eight pounds of N per ton of beets produced is the rate of nitrogen required for optimal sugar production per acre. This seven to eight pounds is the product of residual, or soil test N, plus applied N.

Dr. Susan S. Martin has said, "at season end, yield will be proportional to the amount of radiation captured and utilized by the crop." As spring starts arriving, day length increases until June 21, which is the day with the longest period of sunlight. After this date even though temperatures continue to increase, day length begins to decrease. Therefore it is important to take full advantage of the radiant energy mother nature provides in the form of long days at the front end of the growing season.

To maximize early season growth, it is imperative that nitrogen fertilizer be available to sugarbeet plants by the time they reach the four to eight leaf stage of development. Growth is very rapid from this point until full canopy cover or row closure, since both root and top growth are taking place concurrently. The faster the crop can reach total row closure, the quicker plants will be able to maximize growth by full capture and utilization of the longer periods of sunlight. If there is a nitrogen shortage at this stage of the crop, growth potential is reduced or slowed and opportunity is lost never to be regained.

Once sugarbeets have reached full row closure, top growth should slow to a maintenance level to maintain a leaf area index of three to four. The plant food produced after this growth stage through photosynthesis, goes into leaf maintenance, continued root growth, and sucrose storage in the roots. However, if excess nitrogen is available, sugarbeets will take it up and excessive top growth will result. This top growth comes at the expense of photosynthate (sugar) used to grow the tops that would have been accumulated and stored in the roots.

A leaf area index of three to four allows sugarbeets to capture all of the light energy that is available. Under excessive nitrogen fertilization, a leaf area index as high as six can result  (see figure 1). Increasing leaf area above four will not benefit root yields, but will only reduce sugar content and increase the impurities stored in the roots.

Ideally, by mid to late July, a sugarbeet crop will have used up all of the nitrogen fertilizer applied to the crop. From this time until harvest, sugarbeets are pretty much self sufficient in obtaining adequate nitrogen for growth. Nitrogen used in growth from this point comes from three main sources.

        1. The soil release of mineralizable nitrogen.

        2. Mobilization and reuse of nitrogen accumulated and stored in sugarbeet leaves.

        3. The tap roots ability to remove nitrogen from deeper subsoil levels. (See figure 2)

The type of fall weather we experience in our growing areas always has some impact on both yield and crop quality. Cooler falls result in increased sugar content and beet quality, but does so at the expense of root yield. In cooler periods, photosynthesis and sugar production continue in beets, but the cooler conditions are not as conducive to growth, and more of the sugar produced is stored in the roots as less is used in growth. In unusually warm fall weather, just the opposite occurs as tonnage increases at the cost of stored sugar. Cool fall nights with warm, but not hot, bright sunny days provide the best of both worlds.

Get the sugarbeet crop started and growing as rapidly as possible early in the season. Make certain that nitrogen fertilizer is applied and available to the crop by the time the beets are in the four to eight leaf stage of growth. Do not over fertilize, seven to eight pounds of (soil test plus applied) nitrogen per ton of historical yield is the recommended amount to use. Too much nitrogen late in the season -from mid July on- will not increase root yields, but will stimulate excess top growth at the expense of sugar used for that growth, which should be, but does not get stored in the roots. From this mid July point in the season healthy sugarbeets become almost self sufficient in obtaining adequate nitrogen for optimum growth and sugar production.