Minn-Dak Growers Availing Themselves of Its Benefits - by Mike Metzger*
Were you to hear the words “spent lime,” what would be the first connection popping into your mind?
For many Upper Midwest sugarbeet producers, most likely it would be “disease suppression” or “Aphanomyces reduction,” as this specific topic has been the focus of extensive research and publications in the region over the past decade. Certainly the application of spent lime at recommended rates to an Aphanomyces-infested field can help keep the disease at bay. But there likewise may be some components to spent lime that you probably did not realize. Indeed, the application of this product to your fields can offer a number of “perks” that are overlooked.
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*Mike Metzger is research agronomist with Minn-Dak Farmers Cooperative,
Where Does It Come From?
Spent lime is a byproduct produced by sugar factories as a result of the raw juice purification process. The product itself is generated by heating quarried limestone (calcium carbonate) in a kiln to temperatures that exceed 2,000 degrees Fahrenheit. This extreme heat breaks down the limestone into two components – calcium oxide and carbon dioxide – both of which are injected into the raw juice.
The ensuing chemical reaction gives the calcium oxide a tremendous amount of “charged” surface area that binds to just about everything but sucrose. That ties up most of the raw juice impurities when it is bound back with the CO2 to once again form calcium carbonate. The resulting new “enriched” molecule can then be separated from the purified juice via a series of filters, with the final product being what we call “spent lime.”
Its Nutrient Value
Spent lime offers a nice nutrient supplement (and, in some cases, even a replacement) to the fertilizer normally applied to the fields in the Minn-Dak growing area. Though the application of spent lime will help increase the levels of potassium, calcium, magnesium, sodium and boron present in the soil, its most noticeable effects are nitrogen and phosphorus.
While all sugarbeet factories produce lime as a byproduct, the nutrient load in the spent lime does differ slightly from factory to factory. The data utilized in this article come from a 2014 analysis of the Minn-Dak factory’s spent lime. (In 2004-05, Dr. Albert Sims, University of Minnesota Northwest Research & Outreach Center at Crookston, conducted a study comparing the nutrient analysis of the spent lime produced at the various beet factories in Minnesota and North Dakota. The results of that study can be found in the 2005 Sugarbeet Research and Extension Reports book [Volume 36, January 2006] or online at www.sbreb.org.)
Spent lime at Minn-Dak contains approximately 0.35% nitrogen, which equates to roughly 2.35 pounds of nitrogen per ton of lime. However, it is important to remember that not all of this nitrogen is readily available to the plant and remains tied up in the soil. Researchers at the University of Minnesota estimate that almost 50% of the nitrogen applied would be available for uptake by the crop the following year.
Minn-Dak’s spent lime also contains about 5,000 ppm (0.5%) of actual phosphorus. This means that for every ton of spent lime applied per acre, a grower can account for around 15.58 pounds of phosphorus along with it. As a general rule of thumb, growers will raise soil phosphorus by 1.0 ppm per ton of actual lime applied (Olsen Test). Following university recommendations of seven to 10 tons per acre of lime and accounting for forecasted fertilizer prices, the fertilizer value of the phosphorus alone ranges from $69 to $98 per acre. (See table on next page.) pH Adjustment Spent lime can really help those growers with lower pH levels. Soils with lower pH values typically have excess hydrogen. When spent lime is applied to these types of soils, the calcium, carbonate (CaCo3) in the spent lime chemically binds to the excess hydrogen, forming a water molecule (H2O), carbon dioxide (CO2) and calcium (Ca). Each of these three “new” compounds has its own benefit: Water is self-explanatory; plants “breathe in” the carbon dioxide; and the remaining calcium molecules are available for up take by the crop, helping the plant strengthen its cell walls and improve
its nitrogen efficiency.
Contrary to popular belief and coffee shop talk, application of spent lime will not raise your soil pH above 8.2.
Improved Soil Structure
As a natural additive, calcium is great for the soil. When compared in size to some of the other soil nutrient particles, calcium is huge. On a microscopic level, the comparison is as dramatic as comparing the size of a basketball to a golf ball. The incorporation of these large particles into the existing soil really helps “loosen up” the overall soil structure. This allows for increased water movement and improved drainage, making the soil less prone to compaction issues and providing a lot more porous spaces for the plant’s lateral roots to grow.
The neat thing is that it only gets better with time, as every pass made with a tillage implement, either in-season or between seasons, works the lime a little deeper into the soil profile.
Odds & Ends
There are no negative impacts from spent lime application on rotational crops (wheat, corn, beans, potatoes, etc.). In most cases, university research has shown the spent lime treatment to actually be very beneficial from a yield standpoint.
Spent lime can act as a natural irritant to insects and helps reduce the germination of acid-loving weeds like quack grass. It can even add to the efficiency of certain herbicides — especially those in the triazine class.
Come & Get It
Although lime can be loaded out nearly year-round at Minn-Dak and other companies, the peak months in the Upper Midwest continue to be June through September — including loading out lime during preharvest. This unique system has grown in popularity over the past couple seasons at Minn-Dak and allows any grower who delivers beets to the factory yard during prepile to take advantage of their backhaul by loading up with lime before heading back to the field.
Growers at Minn-Dak Farmers Cooperative currently utilize a little more than twice the amount of lime produced by the factory each year. With all the benefits listed above, we do not expect this trend to slow down for quite some time.
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Editor & General Manager of The Sugarbeet Grower