Coal combustion residue char shows potential as soil amendment |

Coal combustion residue char shows potential as soil amendment

Bijesh Maharjan, soil and nutrient management specialist, UNL Panhandle Research and Extension Center, Scottsbluff
Aerial imagery was collected at bean emergence using a drone. All dark green rows correspond to plots where char has been applied, at varying rates (10, 20, 30, 40, and 60 tons per acre).
Photo courtesy Nebraska Extension |

Research being performed by the University of Nebraska shows that char, a byproduct 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 (SOM). 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 byproduct 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 the Environmental Protection Agency’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.

Aerial imagery early in the season in 2017 showed encouraging evidence of char as a potential soil amendment in a dry edible bean field near Scottsbluff, Neb. The soil of the char trial was calcareous, sandy loam and had less than 1 percent SOM. The trial was in an area under center pivot that has low productivity compared to the rest of the field, probably due to leveling of the field at some point in the past.

The image was taken in mid-July, following char application in mid-May. The same year dry bean yield increased by 12 to 52 percent with char application at various rates (10, 20, 30, 40 and 60 tons per acre). However, the only statistically significant yield increase occurred on the plot where 60 tons of char was applied.

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 the 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 the 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 beans 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, please feel free to contact me at (308) 632-1372.

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

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