Adjusting low soil pH with sugar beet-processing spent lime

The sugar beet processing industry uses large quantities of fine-ground, high-grade calcium carbonate (lime) to purify sucrose in the sugar extraction process. The by-product spent lime retains high reactivity and purity, making an attractive liming material for acidic soils. Application of spent lime is a common practice through the sugar beet producing areas of the upper Midwest and northern Great Plains, where its primary function is the suppression of the soil-borne disease Aphanomyces root rot of sugar beet. The spent lime also contains about 20 lb P₂O₅ per ton, mostly as organic phosphorus impurities gained from sugar refining.

AGVISE Laboratories installed a long-term demonstration project in 2014 to evaluate adjusting low soil pH with spent lime. The project site was located near our Northwood Laboratory. Northwood lies along the beachline of glacial Lake Agassiz, where well-drained coarse-textured soils with low pH are common. We located a very acidic soil with soil pH 4.7 (0-6 inch), which was the perfect site to evaluate lime application. In May 2014, spent lime was applied and incorporated with rototiller. The spent lime quality was very high at 1,500 lb ENP/ton. In Minnesota, lime quality is measured as effective neutralizing power (ENP), which measures lime purity and fineness. Soil pH was tracked over three years (Table 1).

The lowest spent lime rate (2,500 lb ENP/acre) increased soil pH above 5.5. This soil pH reduced aluminum toxicity risk, but it did not reach the target pH 6.0, appropriate for corn-soybean rotation. The highest spent lime rate (10,000 lb ENP/acre) increased soil pH above 7.0 and maintained soil pH for several years. Spent lime is a fine-ground material with high reactivity, so its full effects were seen in the first application year. The project showed that spent lime is an effective liming material for low pH soils.

Table 1. Soil pH (1:1) following sugar beet-processing spent lime application on low pH soil.
Spent Lime	Year
	May 2014	Sept 2014	July 2015	June 2016
lb ENP/acre
0	4.8	4.8	4.7	5.1
2,500	4.8	5.5	5.2	5.4
5,000	4.8	5.6	5.7	5.5
10,000	4.8	7.4	7.0	7.4
Spent lime applied and incorporated September 2008. Soil sampled in fall.