John Lee

Adjusting high soil pH and salinity with sugar beet-processing spent lime

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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 it 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.

We often get questions about correcting high soil pH and salinity with spent lime. Salt-affected soils, saline and sodic, are a common problem across the northern Great Plains. These soils have high soil pH and present numerous agronomic and soil management problems. The soil amendment gypsum (calcium sulfate) is often applied to sodic soils (those with high sodium) to combat soil swelling and dispersion. The spent lime (calcium carbonate) also contains calcium, but it is very insoluble at high soil pH.

Each year, we get many questions about applying spent lime on soils with high pH and salinity. To answer these questions, AGVISE Laboratories installed a long-term demonstration project in 2008 to evaluate adjusting high soil pH and salinity with spent lime. We applied multiple spent lime rates and tracked soil test levels over seven years. There were no significant changes or trends in soil pH (Table 1) or salinity (Table 2). This is no surprise because the initial soil pH was high and buffered around 7.8-8.2, indicating the presence of natural calcium carbonate. If the soil already contains naturally occurring lime, what is the good of adding more lime? Moreover, calcium carbonate is very insoluble, so there is no expectation that more lime will decrease or increase salinity.

Since soil test levels did not change over seven years, we terminated the project in 2014. The research question was a conclusive dud. While spent lime is useful to amend acidic soils and suppress Aphanomyces root rot of sugar beet, it does not help on soils with high pH or salinity.

 

 

Table 1. Soil pH (1:1) following sugar beet-processing spent lime application on high pH soil.
Spent Lime Year Average
2008 2009 2010 2011 2012 2013 2014
ton/acre
1 7.8 7.7 7.9 7.8 7.7 8.0 8.0 7.80
2 7.9 7.9 8.1 7.9 7.9 8.0 8.0 7.94
3 7.9 7.9 8.1 7.9 7.9 8.1 8.1 7.95
4 7.8 7.8 7.9 7.7 7.8 8.1 8.0 7.85
5 7.8 7.8 8.0 7.9 7.9 8.0 8.0 7.90
6 8.0 7.9 8.2 8.0 8.0 8.1 8.1 8.00
Spent lime applied and incorporated September 2008. Soil sampled in fall.

 

Table 2. Soil salinity (electrical conductivity, EC 1:1) following sugar beet-processing spent lime application on moderately saline soil.
Spent Lime Year
2008 2009 2010 2011 2012 2013 2014
ton/acre ——————— dS/m ———————
1 1.5 1.2 1.8 1.1 1.6 1.2 1.8
2 1.9 2.1 2.3 2.5 2.3 2.0 2.0
3 1.9 2.2 2.6 2.5 2.4 1.9 1.9
4 1.0 1.3 1.4 1.2 1.5 1.9 1.9
5 1.7 2.2 2.2 2.3 2.2 1.7 1.7
6 2.6 2.1 2.1 2.9 2.5 1.9 1.9
Spent lime applied and incorporated September 2008. Soil sampled in fall.
John Breker

Soil Salinity Analysis: Which method to choose?

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This submission is courtesy of Dr. Heather Matthees, Research Soil Scientist, USDA-ARS, Morris, MN. It was originally published in the AGVISE Newsletter Fall 2017.

Salt-affected soils are a major problem for agricultural producers, resulting in $12 billion annual losses in crop production across the world. In the northern Great Plains and Canadian Prairies, soil salinity has always existed in some soils of the region, but the problem has become more widespread and severe since a hydrological wet period began in the 1990s.

Salinity is the overall abundance of soluble salts, which compete with plant water uptake and reduce crop productivity. The soluble salts pull soil water toward themselves in the soil solution, which leaves less soil water available for plant uptake. This causes an apparent drought stress, reducing crop productivity and sometimes may kill the plant. Soluble salts are naturally occurring and a product of regional geology in the northern Great Plains and Canadian Prairies. Since the 1990s, the hydrological wet period has raised the groundwater level and allowed saline groundwater to rise toward the soil surface, causing soil salinization. Saline soils are often called “salty,” “sour”, or “white alkali.”

The severity of soil salinity will control which plant species are suitable for crop or forage production. Some crop species like dry bean and soybean are very sensitive to salinity, whereas other crop species like barley and sunflower have good tolerance to salinity. For soils with very high salinity, the only practical forage option may be salt-tolerant perennial grasses. To assess soil salinity, there are two soil analysis methods: saturated paste extraction and routine 1:1 soil water methods.

Saturated Paste Extraction Method

The gold standard in soil salinity research is the saturated paste extraction method. The method requires a trained laboratory technician to mix soil and water into a paste, just reaching the saturation point, which is about the consistency of pudding. The saturated paste rests overnight to dissolve the soluble salts. It is then is placed under vacuum to draw the saturated paste extract. Soil salinity is then determined by measuring the electrical conductivity (EC) of the saturated paste extract.

The saturated paste extraction method is fairly straightforward, but it requires a trained technician, specialized equipment, and over 24 hours to complete the procedure. The procedure is labor intensive and difficult to automate, so it is considered a special analysis service in commercial soil testing. Therefore, it is more expensive than routine soil testing methods. Among soil salinity determination methods, it is considered the most accurate because the soil:water ratio at saturation controls for differences in soil texture and water holding capacity.

Routine 1:1 Soil:Water Method

The routine method for soil salinity assessment is the 1:1 soil:water method, which mixes standard mass of soil (10 g) and volume of water (10 mL) in a soil-water slurry. Soil salinity is then determined by measuring the electrical conductivity (EC) of the soil-water slurry. It is most commonly abbreviated EC1:1.

The method is fast and inexpensive (only 5-10% of saturated paste extraction cost). The low cost per soil sample allows a person to collect more soil samples from various soil depths and multiple locations within a field (e.g. zone soil sampling), which can create a more comprehensive and detailed soil salinity map to evaluate soil salinity presence, severity, and variability. Since soil salinity is so intimately related to soil water movement across the landscape, the soil salinity map also provides information about soil water accumulation and leaching, soil nutrient movement (e.g. chloride, nitrate-nitrogen, sulfate-sulfur), and crop productivity potential.

A general caveat about the 1:1 soil:water method is that the reported values will be lower than the saturated paste extraction method. Fortunately, the two methods are highly correlated. AGVISE Laboratories worked with soil science researchers at North Dakota State University and South Dakota State University to validate the correlation between the two methods using over 2,300 soil samples from the northern Great Plains. You can convert the two methods by multiplying the 1:1 soil:water result by 2.26 to estimate the saturated paste extraction result (Figure 1).

The simple method conversion enables you to quickly and cheaply monitor soil salinity using the 1:1 soil:water method and still utilize the historical soil salinity interpretation criteria based on the saturated paste extraction method.

Figure 1. Soil salinity method conversion between saturated paste extraction and 1:1 soil:water methods.

References

Matthees, H. L., He, Y., Owen, R. K., Hopkins, D., Deutsch, B., Lee, J., Clay, D. E., Reese, C., Malo, D. D., & DeSutter, T. M. 2017. Predicting soil electrical conductivity of the saturation extract from a 1:1 soil to water ratio. Communications in Soil Science and Plant Analysis, 48(18), 2148–2154.