Co-authored with Dr. Eugenia Pena-Yewtukhiw, West Virginia University

We’re getting more questions about biochar (any char made from non-fossil biomass. Can biochar application: a) result in greater carbon (C) sequestration; b) improve soil resilience; c) raise crop yield? Biochar research has been going on for a decade. This is not our first rodeo about biochar as a soil amendment. There were many reports regarding “terra preta”, black soil areas in the Amazon region containing large amounts of char, between 1995 and 2000 (Sombroek, 2003). Biochar is formed by heating/burning organic materials under low oxygen conditions. This is a form of stabilization, chemically similar to composting – easily decomposable/oxidized component compounds are lost or transformed into more stable, recalcitrant constituents. 

The general characteristics of biochar vary with feedstock choice (grass, wood, poultry litter, horse muck) and pyrolysis conditions (especially temperature). Feedstock composition can determine differences in biochar surface area/porosity and salt and ash levels (Nagel et al., 2019). Generally, animal waste chars have greater ash/salt concentrations. Higher pyrolysis temperatures can result in char with greater aromatic C content; with greater resistance to mineralization (carbon dioxide release; Zimmerman et al., 2011) and greater hydrophobicity after soil application (Oginni, 2018). Typically, biochar is low-density (can float away in moving water). 

Reported biochar application rates range widely, between 0.5 and 20 tons/acre. Impacts on soil properties are expected and variable in nature. Ash, if present (is sometimes removed), can increase salt load, raise soil pH, and increase soil nutrient levels (primarily calcium, potassium, magnesium). In sandy soils, biochar sometimes increases water retention, and in some cases, it improves aggregate stability in silty and clayey soils (Nobert et al. 2016). 

Compiling crop response studies, Spokas et al. (2012) found that 20, 30, and 50 percent of the studies reported negative, neutral, and positive yield responses to biochar, respectively. One common generalization was that positive responses were more likely on poor, degraded soils, and neutral/negative responses were more probable on average/good agricultural soils. In Kentucky, the crop response data are limited, but do support the common belief. Table 1 is taken from work done by the USDAARS research group at Western Kentucky University (Sistani et al., 2019).

Sistani et al. (2019) grew no-till corn for grain on a Crider silt loam. The mixed hardwood biochar was applied once, in the spring of 2010, at a rate of 9.5 tons/acre. The poultry litter was applied annually to provide 200 lb N/acre. The fertilizer treatment consisted of annual applications of 200 lb N/acre plus additional phosphate and potash according to soil test-based fertilizer recommendations (Sistani et al., 2019). The 2010 and 2011 production seasons were dry, and there was little response to any individual treatments (Table 1). The year 2013 was much better, and there was a large response to both fertilizer and poultry litter addition. Biochar addition resulted in a consistent 10 to 11 bu/acre yield reduction, regardless of the seasonal weather. Biochar did not appear to have increased soil or crop resilience on this productive soil (Table 1). 

In West Virginia, poultry litter biochar was added at 14 tons/acre to two reclaimed mine land sites and two marginal agricultural farm sites (Nobert et al. 2016). Six cultivars of a biofuel feedstock species, willow, were grown. Plant growth (height) and dry matter accumulation were measured. Young plant growth in the first year was strongly positively influenced by biochar application, averaging 9.4 inches greater height regardless of the site type. Corresponding dry matter accumulation was 72% greater. Such a large beneficial response on more marginal soils also aligns with the current general understanding. 

These examples illustrate the range in plant response that might be observed with biochar amendment and should serve to caution those who expect positive benefits under all soil conditions. The range in biochar properties, combined with the range in chosen application rates, will also probably cause a range in the numerical value of any soil biological, chemical and physical property response. This will make the prediction of soil health benefit magnitude from biochar addition difficult.

References 

Oginni, O.J. 2018. Characteristics of Activated Carbons Produced from Herbaceous Biomass Feedstock. Ph.D. Dissertation. West Virginia University. 

Nagel, K., N.O. Hoilett, M.A. Mottaleb, M.J. Meziani, J. Wistrom and M. Bellamy. 2019. Physicochemical characteristics of biochars derived from corn, hardwood, miscanthus, and horse manure biomasses. Commun. Soil Sci. Plant Anal. https://doi.org/10.1080/00103624.2019.1594881  

Nobert, H.A., D.W. McGill, S.T. Grushecky, J.G. Skousen and J.L Schuler. 2016. Salix spp. as a biomass crop: Investigating its potential on mined lands and the use of biochar as a soil amendment. JASMR. 5:58-76. DOI: 10.21000/JASMR16020058 

Sistani, K.R., J.R. Simmons, M. Jn-Baptiste and J.M. Novak. 2019. Poultry litter, biochar, and fertilizer effect on corn yield, nutrient uptake, N2O and CO2 emissions. Environments 6 (55) doi:10.3390/ environments6050055 

Sombroek, W. 2003. Foreword. In: Amazonian Dark Earths: Origin, Properties, Management. Lehman, J., D.C. Kern, B. Glaser and W.I. Woods (eds.). Kluwer Academic. New York. 

Spokas, K.A., K.B. Cantrell, J.M. Novak, D.W. Archer, J.A. Ippolito, H.P. Collins, A.A. Boateng, I.M. Lima, M.C. Lamb, A.J. McAloon, R.D. Lentz and K.A. Nichols. 2012. Biochar: A synthesis of its agronomic impact beyond carbon sequestration. J. Environ. Qual. 41:973-989. 

Zimmerman, A.R., B. Gao and M. Ahn. 2011. Positive and negative carbon mineralization priming effects among a variety of biochar-amended soils. Soil Biol. Biochem. 43:1169.

Citation: Grove, J., 2025. Pena-Yewtukhiw, E., 2025. Biochar. Kentucky Field Crops News, Vol 1, Issue 1. University of Kentucky, January 17, 2025.

Eugenia Pena-Yewtukhiw  Director, Soil Testing Laboratory  Assoc. Professor, Soil Physics and Management West Virginia University.