BURLEY — Managing nitrogen has always been a balancing act for sugar beet growers. Plants need nitrogen early in the season to put on weight, but too much late in the year can cause sugar levels to fall.
Now Amalgamated Sugar Co. has found a strong correlation between nitrate and conductivity, a measure of impurity. The grower-owned cooperative just paid its members using a new formula that includes nitrate levels rather than just paying how big and sweet the beets are.
Pat Laubacher, vice president of agriculture at Amalgamated, said the intention of the new formula is twofold: to improve factory efficiency and to protect the environment. Growers whose nitrate levels were higher than the company average saw discounts ranging up to $4 per ton, while those whose levels were lower received a bonus of up to $1.30 per ton.
While most think of sugar factories as turning beets into sugar, Laubacher said factories are really removing impurities from the beet sugar. The higher the impurities, the longer the factories must run and the higher the operational costs.
Ian Kihara, manager of technical services for the sugar company, told growers that a decrease of just 0.5 percent in total thick juice purity — he used the example of 93.5 percent falling to 93 percent — costs the company $2 million. Spreading that $2 million in additional costs across 7 million tons produced means a 30-cent per ton reduction in each grower’s check.
Nitrogen management and the impact of nitrates in the factories was the primary focus of the annual Snake River sugar beet conference held in Burley.
Conductivity is a measure of the electricity that is able to flow through a solution, Kihara explained. It is linked to total dissolved salts and nitrate is a salt.
“Conductivity is not a measure of how good your beets are, but how ‘not-good’ they are,” he said.
Salts dissolve in solution but sugar does not. As beets are processed a syrup is formed and water evaporated from it to form sugar crystals. The evaporated water is called molasses and can be refined again to make sugar.
When salt levels are too high in the thick syrup, more caustic must be used to remove those impurities, which reduces extraction rates. Kihara said nitrate is the primary controllable factor followed by potash or potassium. Every 1 pound of potash in the thick juice sends 3.5 pounds of sugar into the molasses stream rather than being processed immediately into sugar crystals.
Growers can lower nitrate levels by following the company’s nitrogen and potassium application recommendations based on a 3-foot soil sample, said Clarke Alder. He runs the company’s sugar quality improvement department. Amalgamated offers free soil sampling and fertilizer recommendations to all 750-or-so members.
“You want to manage nitrogen so beets run out of nitrogen and test low at harvest,” he said.
Field selection is also important, Alder said. Beets are more tolerant of saline soils and so growers should avoid fields with high salt content or fields that have been manured or composted recently.
A long-term manure study done at the Agricultural Research Service in Kimberly showed that manure increased yields by 1.5 to 4 tons per acre but heavier manure application rates lowered recoverable sugar by 1 to 3 percent.
But another study showed that manure applied five years before beets were grown still showed an increase in yield without affecting sugar quality.
“There can be an advantage to manure as long as enough time has gone by and a moderate amount was applied to start with,” ARS soil scientist David Tarkalson said.
Tarkalson also encouraged Idaho growers to consider changing their nitrogen management from a yield-based approach to one that looks at total available soil nitrogen and commercial fertilizer applications. Growers in Minnesota and North Dakota have already made the switch.
The problem with the yield based approach is that today’s yields are increasing more rapidly than fertility recommendations, Tarkalson said. For example, fertility work done in the 1970s recommended growers apply 8 to 9 pounds of nitrogen per ton of expected yield but yields were just 25 tons per acre at the time.
Today growers are advised to apply 5.5 pounds of nitrogen per ton of expected yield, but that recommendation was based on 35-ton per acre beets. Yields have been increasing by 1 ton per acre annually since Roundup Ready technology was introduced in 1995. Prior to 1995 the average yield gain was 0.25 tons per acre.
Researchers, agronomists and growers all thought they were doing a good job of reducing nitrogen use when the recommendation was lowered to 5.5 pounds per ton but when the rate is multiplied by today’s yield, the total amount of nitrogen exceeds what was applied in the 1970s at the higher rate.
Tarkalson estimates that beets in southern Idaho could be raised on 170 pounds of nitrogen per acre including both the soil available nitrogen based on soil sampling and commercial fertilizer.
To use the static model rather than the yield-based approach, growers should start with a 3-foot soil sample in the spring. Subtract the amount of soil-available nitrogen from either 170 or 180, depending on if the soil is loamy or sandy. The resulting number is the amount of commercial fertilizer to apply per acre.
Based on what he’s seen from analyzing spring soil samples, only about 47 percent of beet fields need nitrogen fertilizer, the rest have sufficient soil-available nitrogen levels.