Protecting Roots

Topping Too Far Ahead: "Don't Do It"

Published in the August 2012 Issue Published online: Aug 08, 2012 Greg Dean
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There are many reasons growers top or defoliate too far ahead. Some reasons are valid, while others are not. Topping ahead more than you will dig in a day is not advisable.

Growers wanting to maximize profit should begin and end the day harvesting sugarbeets less than 30 minutes behind the defoliator.

This concept is most critical during the hot and cold parts of harvest. The hot and cold portions are usually at the first and end of harvest, respectively. Topping too far ahead is less important during the middle part of harvest. Since we cannot predict the days it will be too warm or too cold to defoliate ahead, it is much easier to develop the practice of staying caught up with the defoliator at all times.

By not defoliating, sugarbeet tops remain on, insulating and protecting the sugarbeet roots from hot and cold temperatures. The article, "Topping too far Ahead," can be summarized by these three words: "Don't do it."

 

HIGH TEMPS

Topping ahead during hot and cold parts of the harvest season can be very damaging. The sugarbeets shown in Picture 1 are an example of beets received when air and sugarbeet pulp temperatures were too high.

These sugarbeets had only been in the pile for about 10 days. The picture clearly shows beet juice running out of the bottom of the pile.

What went wrong?

The ambient air and sugarbeet pulp temperatures were too high. Some growers were topping too far ahead. This resulted in sugarbeets that would not store long enough to be processed.

 

COLD TEMPS

The sugarbeets in Pictures 2 and 3 are examples of sugarbeets received when the beets were too cold.

After three days of extreme frost without tops, then thawing out, the sugarbeets were delivered and piled.

The pictures were taken about 15 days after the sugarbeets had been piled. The pile was starting to sink and there was large amount of steam coming out of the top of the pile.

There was also a lot of mold, as seen in Picture 3. Without the additional insulation of the sugarbeet tops, the frost penetrated deeper than it would have otherwise.

Sugarbeets without tops do not recover after frost damage the same as sugarbeets that have the tops left on.

The results are the same as hot weather damaged sugarbeets; there is a very limited storage life.

 

RESPIRATION

The sugarbeet is a bi-annual plant. This means that the sugarbeet is intended to live for two years.

In the first year, the sugarbeet builds a root and stores sugar. In the second year, the sugarbeet uses stored sugar to send up a seed stalk and produce seed.

Sugarbeet growers intervene in the middle of that two-year process by harvesting the sugarbeet, storing it in piles and processing it into sugar.

While in the pile, the sugarbeet root is still alive. It stays alive through a process called respiration. To understand respiration, it helps first to understand photosynthesis.

Photosynthesis is the plant taking in solar heat and light, combining it with water and minerals from the soil to make plant food.

That plant food, or sugar, is used for making a root or for storing sugar. Photosynthesis is a process that takes place in the plant leaf.

Respiration is the opposite of photosynthesis. During respiration, the sugarbeet uses sugar stored in the root to survive giving off heat and moisture. Both heat and moisture are hazardous to stored sugarbeets.

Under normal storage conditions, the rate of respiration is one quarter of a pound of sugar per ton per day.

For every 15-degree increase in temperature the rate of respiration doubles. Assuming that beets stored in a sugarbeet pile at 38 degrees have the normal rate of respiration and we increased the temperature by 15 degrees to 53 degrees, the respiration rate would double to one-half of a pound per ton per day.

If it increased an additional 15 degrees to 68 degrees, it would double again to one pound per ton per day.

At these rates of increase, it does not take long before steam is coming out the top and sugarbeet juice is running out the bottom as seen in Pictures 1, 2 and 3.

 

UNTOPPED VS. TOPPED

There is a difference between sugarbeets that are topped and sugarbeets that are untopped.

During the fall of 2003, we used data loggers to collect temperature information near the reverse receiving station.

We collected temperatures in 30-minute intervals, from late September until mid-November, in sugarbeets that were topped and in beets that had tops on.

We collected ambient air temperatures as well as temperatures two inches down from the crown in topped and untopped beets. This was done by boring a hole into the sugarbeet, and the thermocouple was located approximately in the center of the sugarbeet two inches down into the crown.

The information in Figure 1 shows ambient temperature from 10 a.m. on October 31, 2003, through 10 p.m. on November 1, 2003.

Please note: the temperature peaked about 4 p.m. on both days (about 49 degrees), and the high-to-low and low-to-high was about a 29-degree change each way or 58-degree total change.

The next graph in Figure 2 adds the temperatures captured, representing what is happening in the sugarbeets that have been topped.

The top temperatures peak about the same time of day. The temperatures in beets with no tops peak out at about 62 degrees on the first day and 58 degrees on the second day.

This is a full 20 degrees higher. This is significant; remember, respiration rates double every 15 degrees.

It is apparent that the sun is radiating down on the sugarbeet, causing it to become much warmer than it would have been if the tops had been left on.

The beets reached a low of about 22 degrees. The high-to-low and low-to-high the next day was 75 degrees. Compare this to the 58-degree change of the ambient air temperature.

In Figure 3 the temperatures of sugarbeets not topped were added.

The temperatures of sugarbeets with their tops on acted very similar to the ambient air temperatures.

The difference does not come in the heat of the day but in the cold parts of the day. Sugarbeet tops help insulate the sugarbeet root from the heat of the sun and from the frigid air temperatures.

Sugarbeets with their tops on are 14 degrees warmer than the outside air temperature and six degrees warmer than beets without tops.

Beets having tops on are significantly warmer, causing less frost damage. Frost damage in sugarbeets causes the sugarbeet to repair itself.

Repairs cause the sugarbeets to respire. Respiration causes beets to use sugar and create heat. The heat causes more respiration. The increased heat causes more respiration, therefore, using more sugar, and creating even more heat, causing respiration rates to spiral out of control.

Out-of-control respiration causes sugarbeets to spoil before they can be processed.

 

DEFENDING TOPS

The final view of this graph in Figure 4 brings all the collected information together.

It shows that beet tops do an excellent job of insulating and protecting sugarbeet roots from the heat and the cold.

Combining this information with what is known about respiration, it can be concluded that the sugar lost to excess respiration could be minimized by harvesting beets that have not been defoliated for long periods of time ahead of digging.

DEFOLIATE OPTIONS

Delivering sugarbeets cooler and without frost to the pile helps to reduce respiration rates. This can be accomplished if growers do not defoliate ahead during times of heat or cold. This does not mean the grower must dig slower, however. There are other options.

The Elwyhee, Idaho, District growers have generally adopted the practice of using a straw shredder ahead of their defoliator.

Picture 4.

They started doing this as a result of the weed pressures and problems with weeds at harvest. They have continued to use shredders because it allows them to go one to two gears faster with their defoliators.

Defoliators can stay ahead without delaying the sugarbeet digger and without having to defoliate ahead.

They adjust the shredder about one to three inches above the crown of the sugarbeet. Picture 5.

This allows the shredder to do most of the work. The shredder is also much cheaper to maintain than the defoliator.

Growers are almost able to double the number of acres the defoliator covers between flail changes.

Another benefit of the shredder is the fact that the beet tops do not ball up, as they tend to do when all the tops are being rolled in the defoliator resulting in few, if any, plug-ups of the beet digger.

One sugarbeet grower told me that the additional tractor used about the same amount of diesel fuel as was saved on the defoliator tractor.

The main advantage is that growers are able to do a better job of defoliating, stay ahead of the beet digger and not have to top ahead. Picture 6.

 

DOLLAR SIGNS

The pie chart in Figure 5 represents the money made from sugar sold.

The small slice of the pie represents the grower's portion and is determined by the amount of tons delivered and the sugar content.

The grower has control of this part of the pie by application of good agronomic practices. The size of the pie is largely determined by the price of sugar in addition to how sugarbeets store.

While the price of sugar is out of sugarbeet grower's control, they can have an affect on how sugarbeets store.

Growers learning and applying knowledge of sugarbeet respiration (and not topping too far ahead) can have a positive affect on reducing sugar storage losses.

Sugarbeet respiration rates can be minimized and profits maximized when growers do not top too far ahead.