Carl A. Bradley

Content and Potential Availability of Selected Nutrients in Field‐Applied Sugar Beet Factory Lime

Factory lime generated during sugar beet processing contains phosphorus (P). Factory lime collected from seven sugar beet factories in North Dakota and Minnesota had P concentrations ranging from 3470 to 7043 mg P kg−1. Soil collected from two field trials one and two growing seasons after factory lime application was analyzed for pH changes and soil‐test P (STP). At one site, soil pH increased after both growing seasons, as did STP, indicating a continued release of P as the factory lime dissolved and reacted with the soil. At the second site, increased soil pH and STP were evident after one growing season, but a few months later the pH had no further change and STP decreased. The data suggest factory lime has the potential to supply P to a growing crop, but actual proportion of P available from the factory lime could not be quantified from these experiments.

Field applications of sugar factory spent lime: Effects on soil phosphorus

Spent lime generated during the purification process of raw sugar beet juice historically has been stockpiled near the factory sites. The seven sugar beet processing factories in Minnesota and North Dakota generate approximately 454,000 Mg (500,000 tons) of spent line annually on a dry weight basis. In recent years, field application of spent lime has been shown to reduce the incidence of Aphanomyces root rot in sugar beet, a disease increasing in prevalence in sugar beet producing regions. In Minnesota and North Dakota, some growers field apply spent lime for a number of reasons, including a perception that more calcium is needed in these mostly calcareous soils, improved productivity of other crops in rotation with sugar beet, and reduced root disease in sugar beet. In many cases the scientific evidence for the improved production due to the application of spent lime has not been documented. The effect of spent lime on Aphanomyces root rot in sugar beet is currently undergoing intensive study. Spent lime is the result of precipitation of calcium carbonates and many impurities from the raw sugar beet juice. Laboratory analysis of spent lime indicates a significant phosphorus component. However, it has been speculated that this P is chemically tied up as calcium phosphate and is not soluble, and thus not available to a growing crop once applied to the soil. as inin the spent lime is not known, but some have speculated it is tied up as calcium phosphates and would not be available to a growing crop once applied to the soil. Our objectives were to: 1) determine the variability of spent lime P content from various sugar beet processing factories, and; 2) determine the effect offield applied spent lime on soil test P levels. Objective 1: Spent lime was collected from each of the seven sugar beet processing factories in Minnesota and North Dakota (American Crystal at Drayton, East Grand Forks, Crookston, Hillsboro, and Moorhead; Minn-Dak Farmers Cooperative; and Southern Minnesota Beet Sugar Cooperative). Three sub samples of spent lime were collected on three dates: November 17, 2004; January 19,2005; and March 17,2005 from each factory-representing the early, midxad term, and late-term sugar beet processing season. Spent lime was collected just as it was expelled from the factory proper, and before it was hauled to the stockpile. The spent lime samples were brought to the University of Minnesotas Northwest Research and Outreach Center where they were dried, digested, and analyzed for total P concentration. The P content in the spent lime from the various sugar beet processing factories ranged from 3470 to 7073 mg P kg-lover the three sampling dates. There was variation among sampling dates from a single factory as well as variation across factories. When averaged across all sampling dates, the two P content extremes appeared in spent lime from the Drayton factory, average of 3827 mg P kg-I; and from the Moorhead factory, average of 5627 mg P kg-I . Averages of spent lime at the other factories were 4259 (Crookston), 5135 (East Grand Forks), 5404 (Hillsboro), 4952 (Minn-Dak), and 5580 (So. Minn) mg P kg-I. The field application of 10 Mg spent lime ha-I (4.5 ton A-I) would range from the equivalent of 89 kg P20 5 ba1 (Drayton) to 131 kg P20 5 haJ (Moorhead).