Effect of biochar type on macronutrient retention and release from soilless substrate

Authors: Altland, James; Locke, James

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2013
Publication Date: 11/20/2013
Publication URL: http://handle.nal.usda.gov/10113/58152
Citation: Altland, J.E., Locke, J.C. 2013. Effect of biochar type on macronutrient retention and release from soilless substrate. HortScience. 48(11):1397-1402.

Interpretive Summary: Biochar is the charred organic matter that remains after pyrolysis (burning) of biomass or manure. Biochars from different feedstocks yield different properties as a result of their differing particle sizes at the time of pyrolysis, inherent ash content of the feedstock, pyrolysis conditions, and storage conditions after processing. The objective of this research was to determine the influence of three different biochar types on nitrate, phosphate, and potassium retention and leaching in a typical greenhouse soilless substrate. The three biochar types included: gasified rice hull biochar (GRHB), sawdust biochar (SDB), and a bark and wood biochar (BWB). All three biochar types evaluated in these two experiments affected macronutrient retention and release, but each macronutrient responded differently, and each biochar type had a different impact. All biochar amendments affected nitrate release by temporarily absorbing nitrate and releasing it slowly. This could result in less drastic and fewer spikes between high and low nitrate availability in the soil solution. The impact of biochar amendment on phosphate and potassium retention and release was more variable within and across the two experiments. The most interesting aspect of phosphate and potassium release was the high levels of both nutrients provided by the GRHB amendment. This material was a net source of phosphates and potassium, and when incorporated into a greenhouse substrate at 10% by volume, may provide enough of these two nutrients without the need to provide additional phosphorus or potassium fertilizers.

Technical Abstract: A series of column studies were conducted to determine the influence of three different biochar types on nitrate, phosphate, and potassium retention and leaching in a typical greenhouse soilless substrate. Glass columns were filled with 85 sphagnum peat moss : 15 perlite (v:v) and amended with 10% by volume of three different biochar types including: gasified rice hull biochar (GRHB), sawdust biochar (SDB), and a bark and wood biochar (BWB). Columns were drenched with nutrient solution and leached to determine the impact of biochar on nutrient retention and leaching. Nitrate release curves were exponential and peaked lower, at later leaching events, and had higher residual nitrate release over time with each biochar amendment. The impact of biochar amendment on phosphate retention and release was more variable within and across the two experiments. In both experiments, the GRHB was a net source of phosphate, providing more phosphate to the system than the fertilizer application and hence obscuring any retention and release effect it might have. Potassium release varied by amendment type within each experiment, but within each amendment type was relatively consistent across the two experiments. All biochar types were a source of potassium, with GRHB providing more than SDB, but both providing far more potassium than the fertilizer event. The BWB amendment resulted in more leached potassium than the control substrate, but relatively little compared to GRHB and SDB amendments.