IBI Research Summary:

Impact of Biochar on Soil Moisture

Updated: 5 February 2010

Authors: Kelpie Wilson and Julie Major, PhD

Note: IBI Research Summaries are intended to provide answers about biochar science for the general public. These summaries are based on IBI’s review of published scientific literature. As this literature is updated, IBI will update these summaries. Please contact IBI at info@biochar-international.org if you have questions or information to share.

Question: Does biochar help soils retain moisture?

More studies, especially field studies, are needed on the question of water retention with biochar, but the results so far consistently show benefits in sandy soils where this function is most needed.

The Australian national science agency, CSIRO, released a comprehensive review (Biochar, climate change and soil: A review to guide further research) of biochar in February 2009, co-authored by Rothamsted Research and Newcastle University in the UK. The CSIRO review looked at work done on biochar impact on soil moisture retention. While it found few studies that directly addressed soil moisture retention with biochar, it found that “Many studies where the effect of biochar on crop yield has been assessed have cited moisture retention as a key factor in the results.”

CSIRO cited a study (Gaskin et al., 2007) that found water retention doubled in a loamy sand soil, and a study of Terra Preta (Glaser et al., 2002) that showed water retention was18% higher than adjacent highly-weathered tropical soil.

In a laboratory study by Novak et al. (2009), where different biochar types were added to a loamy sand, biochar either had no significant effect or increased the water holding capacity of the soil. Chan et al (2007) obtained similar results working with a hardsetting Australian soil, with pot trials. Asai et al. (2009) applied biochar to field soil cropped to upland rice at several locations in Laos, and found improved surface infiltration of water.

Also in the field, Major et al. (2009) found that biochar application to a clayey savanna soil of Colombia increased surface water infiltration. Although infiltration is different from moisture holding capacity, if more moisture enters the soil during rain events, more can then potentially be retained by soil.

A case study in Ghana illustrates the significance of biochar augmented water retention in a dryland crop:

Case Study 5 – Example of highly diverse cropping system (maize, yam) with secondary forest in Ghana managed with biochar over 20 years. Farmer reports 100 percent increase in yields. “Her perception is that the underlying mechanism for the effects she sees is entirely physical, citing two factors: enhanced rainwater infiltration and enhanced soil moisture retention. In drought-susceptible sandy soils – prevalent in most parts of Ghana – crop performance is considerably governed by the timing and extent of rainfall, and its effect on crop establishment and maturation.” From: Lehmann, C.J. and Joseph, S., 2009. Biochar systems. In: Lehmann, C.J., Joseph, S. (Eds.), Biochar for environmental management: science and technology. Earthscan.

REFERENCES ON THE IMPACT OF BIOCHAR ON WATER RETENTION:

Asai, H., Samson, B.K., Stephan, H.M., Songyikhangsuthor, K., Homma, K., Kiyono, Y., Inoue, Y., Shiraiwa, T., Horie, T., 2009. Biochar amendment techniques for upland rice production in Northern Laos 1. Soil physical properties, leaf SPAD and grain yield. Field Crops Research 111, 81-84.

Chan, K.Y., Van Zwieten, L., Meszaros, I., Downie, A., Joseph, S., 2007. Agronomic values of greenwaste biochar as a soil amendment. Australian Journal of Soil Research 45, 629.

Gaskin, J.W., Speir, A., Morris, L.M., Ogden, L., Harris, K., Lee, D., Das, K.C. (2007) Potential for pyrolysis char to affect soil moisture and nutrient status of loamy sand soil. In: Georgia Water Resources Conference. University of Georgia.

Glaser, B., Lehmann, J., Zech, W. (2002) Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review. Biology and Fertility of Soils 35, 219-230.

Major, J., Steiner, C., Downie, A., Lehmann, J. (2009) Biochar effects on nutrient leaching. In: Lehmann, C.J., Joseph, S. (Eds.), Biochar for environmental management: science and technology. Earthscan.

Major, J., Lehmann, J., Rondon, M., Goodale, C., 2009. Fate of soil-applied black carbon: downward migration, leaching and soil respiration. Global Change Biol., doi: 10.1111/j.1365-2486.2009.02044.x.

Novak, J.M., Lima, I.M., Xing, B., Gaskin, J.W., Steiner, C., Das, K.C., Ahmedna, M., Rehrah, D., Watts, D.W., Busscher, W.J., Schomberg, H., 2009. Charcaterization of designer biochar produced at different temperatures and their effects on a loamy sand. Annals of Environmental Science 3, 195-206.