Coal combustion residue char shows potential as soil amendment

Research being performed by the University of Nebraska shows that char, a by-product of a local sugar plant, has potential to improve soils in the region. But more research is needed.

Proper soil management is necessary to sustain long-term agricultural productivity. Soil loss through erosion or run-off hurts agricultural production and also has environmental implications.

Many fields in the Nebraska Panhandle have been leveled for irrigation, intensively farmed or have been affected by wind and water erosion, all of which can decrease soil organic matter. Lack of SOM is a significant indicator of a degraded soil.

Plants grown on degraded soil are prone to less vigorous foliar growth, chlorosis, poor root development and poor emergence due to soil crusting. Furthermore, lighter colored soils low in SOM warm up more slowly and have less potential to produce nutrients from mineralization. Many intensively cultivated soils in the Great Plains have lost 30 to 50 percent of the original SOM level.

It appears that char, a by-product from Western Sugar Cooperative plants, has potential to improve soils in the region. Char is a coal combustion residue. Unlike coal ash from a regular coal-powered power plant, char has 30 percent carbon by weight and some other nutrients beneficial to crops.

Trace metal content in char is below EPA’s screening limit. Char is also different from biochar, which is produced by pyrolysis (burning without oxygen) of biomass. Biochar has a higher carbon content, sometimes above 80 percent, but it will be cost prohibitive to use biochar in agriculture, as there is no production to supply biochar in volume.

Several research projects are underway at the UNL Panhandle Research and Extension Center to evaluate use of char in agriculture.

In 2017, spring was cool and wet and there were chlorosis issues. Char might have improved aeration and/or infiltration by improving soil physical properties and that could have led to some beneficial effects. It would require at least a few years of monitoring of this field to document any other significant benefits of char with respect to agronomic productivity or soil properties.

Char at 60 tons per acre is at high end, mainly for economic reasons. Because of cost associated with transport and field application, the chosen rate of char should be economically feasible.

Another char study initiated in 2016 in a different crop rotation system in the UNL High Plains Ag Lab in Sidney (wheat-corn-pea) and in Panhandle Center Mitchell Ag Lab (corn-beet-corn-dry bean) showed neither harmful nor beneficial effects on crop yield in the first year of char application. However, in the second year (2017), dry bean in Scottsbluff and peas in Sidney showed yield increases with char. In both cases, yield increase plateaued at about 20 tons per acre of char.

Like any good and constructive work, it will take a number of years to improve soils enough to eventually enhance yields. We at UNL will continue our work on char evaluating its short- and long-term effects on soils and crop production. For more information, contact me at 308-632-1372.

We acknowledge Western Sugar Cooperative for providing resources and support to conduct research trials.