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Sugarbeet Growers Magazine March 2014 : Page 14

— Spent Lime — A Sound Investment Minn-Dak Growers Availing Themselves of Its Benefits By Mike Metzger* W ere you to hear the words “spent lime,” what would be the first connection popping into your mind? For many Upper Midwest sugar-beet producers, most likely it would be “disease suppression” or “Aphano-myces reduction,” as this specific topic has been the focus of extensive re-search and publications in the region over the past decade. Certainly the application of spent lime at recom-mended rates to an Aphanomyces-in-fested 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. Where Does It Come From? Spent lime is a byproduct produced * Mike Metzger is research agronomist with Minn-Dak Farmers Cooperative, Wahpeton, N.D. by sugar factories as a result of the raw juice purification process. The product itself is generated by heating quarried limestone (calcium carbon-ate) in a kiln to temperatures that ex-ceed 2,000 degrees Fahrenheit. This extreme heat breaks down the lime-stone 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 su-crose. That ties up most of the raw juice impurities when it is bound back with the CO 2 to once again form cal-cium carbonate. The resulting new “enriched” molecule can then be sepa-rated from the purified juice via a se-ries 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 lev-els of potassium, calcium, magnesium, sodium and boron present in the soil, its most noticeable effects are nitrogen and phosphorus. While all sugarbeet factories pro-duce 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 fac-tory’s spent lime. (In 2004-05, Dr. Al-bert Sims, University of Minnesota Northwest Research & Outreach Cen-ter 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 Re-search 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 ni-trogen 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 Min-nesota 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 con-tains 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 recommen-dations of seven to 10 tons per acre of lime and accounting for forecasted fer-tilizer 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 cal-cium, carbonate (CaCo 3 ) in the spent lime chemically binds to the excess hy-drogen, forming a water molecule (H 2 O), carbon dioxide (CO 2 ) and cal-cium (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-Photo: Mike Metzger 14 THE SUGARBEET GROWER March 2014

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