Re: [EXTERN] Re: [Biochar] New data re biochar particle size #sizing

Claudia Kammann

Hi Tom,


the paper is open access, I downloaded it and can send it if group members are interested.


thanks for the leg-up –




Von: <> Im Auftrag von Tom Miles
Gesendet: Montag, 20. April 2020 17:29
Betreff: [EXTERN] Re: [Biochar] New data re biochar particle size


From a recent review of biochar in biofilters:


A meta-analysis98 found that amendment of soil with biochar increases saturated hydraulic conductivity by 25%. Another study found biochar amendment to increase saturated hydraulic conductivity by 328% in clay-rich soil but decrease by 92% and 67% in sand and organic soils, respectively.99. . .The effect of biochar addition on hydraulic conductivity of biofilter media will depend on the differences in particle size of the biochar and the sand55,97 and may also depend on the biochar application rate. Addition of biochar to sand media reduced the hydraulic conductivity at higher biochar application rates (>15%),100 and a ten-fold decrease in hydraulic conductivity compared to sand-only was observed by Ray et al.54 when mixing sand (0.60.85 mm) with finer biochar particles (0.10.3 mm). On the contrary, biochar application rates of 0.52% only led to minimal decreases in hydraulic conductivity of a sandy loam soil.101


54 J. R. Ray, I. A. Shabtai, M. Teixidó, Y. G. Mishael and D. L. Sedlak, Polymer-Clay Composite Geomedia for Sorptive

Removal of Trace Organic Compounds and Metals in Urban Stormwater, Water Res., 2019, 157, 454462, DOI: 10.1016/j.



55 S. K. Mohanty, R. Valenca, A. W. Berger, I. K. M. Yu, X. Xiong, T. M. Saunders and D. C. W. Tsang, Plenty of Room for Carbon on the Ground: Potential Applications of Biochar for Stormwater Treatment, Sci. Total Environ., 2018, 625, 16441658, DOI: 10.1016/j.scitotenv.2018.01.037.


97 Z. Liu, B. Dugan, C. A. Masiello, R. T. Barnes, M. E. Gallagher and H. Gonnermann, Impacts of Biochar Concentration and Particle Size on Hydraulic Conductivity and DOC Leaching of BiocharSand Mixtures, J. Hydrol., 2016, 533, 461472, DOI: 10.1016/j.jhydrol.2015.12.007.


98 M. O. Omondi, X. Xia, A. Nahayo, X. Liu, P. K. Korai and G. Pan, Quantification of Biochar Effects on Soil Hydrological

Properties Using Meta-Analysis of Literature Data, Geoderma, 2016, 274, 2834, DOI: 10.1016/j.geoderma.2016.03.029.


99 R. T. Barnes, M. E. Gallagher, C. A. Masiello, Z. Liu and B. Dugan, Biochar-Induced Changes in Soil Hydraulic Conductivity and Dissolved Nutrient Fluxes Constrained by Laboratory Experiments, PLoS One, 2014, 9(9), e108340,

DOI: 10.1371/journal.pone.0108340.

100 P. de Rozari, M. Greenway and A. El Hanandeh, Nitrogen Removal from Sewage and Septage in Constructed Wetland

Mesocosms Using Sand Media Amended with Biochar, Ecol. Eng., 2018, 111, 110, DOI: 10.1016/j.ecoleng.2017.11.002.


101 H. M. Ibrahim, M. I. Al-Wabel, A. R. A. Usman and A. Al-Omran, Effect of Conocarpus Biochar Application on the

Hydraulic Properties of a Sandy Loam Soil, Soil Sci., 2013, 178(4), 165173.


Ref: Ref Biochar-augmented biofilters to improve pollutant removal from stormwater – can they improve receiving water quality?† Alexandria B. Boehm, *ab Colin D. Bell,bc Nicole J. M. Fitzgerald,bc Elizabeth Gallo, bc Christopher P. Higgins, bc Terri S. Hogue, bc Richard G. Luthy, ab Andrea C. Portmann,bc Bridget A. Ulrichd and Jordyn M. Wolfand bce


From: <> On Behalf Of Nando Breiter
Sent: Monday, April 20, 2020 7:04 AM
Subject: Re: [Biochar] New data re biochar particle size




Here's what I read in the abstract, emphasis mine:


"Biochar was most effective in improving soil water properties in coarse-textured soils with application rates between 30 and 70 t/ha. The key factors influencing biochar performance were particle size, specific surface area and porosity indicating that both soil-biochar inter-particle and biochar intra-particle pores are important factors. To achieve optimum water relations in sandy soils (>60% sand and <20% clay), biochar with a small particle size (<2 mm) and high specific surface area and porosity should be applied. In clayey soil (>50% clay), <30 t/ha of a high surface area biochar is ideal."


The abstract seems to be recommending small particle size. Small biochar particles promote aggregate formation, and in my simple understanding, aggregates store more water than anything else in soil. 


Cutting to the chase, the only thing that matters is the effect on your crop, expressed in the paper as the permanent wilting point, the point at which your crop is going to die if it doesn't rain (or is irrigated) very soon. The abstract reports an average improvement of 16.7% with biochar. 


The paper cites a price range of ... well I'll just quote it. "Depending on feedstock used, the price of biochar could range from US$ -222 to 584/t". It goes on to say that "Biochar application rate above 70 t/ha may not be economical in regard to effect on water relations in soil. Even using an application rate of 30 t/ha could amount to US $17,520/ha." 


An application rate of 70t/h at a cost of U$584 per tonne would total $40,880 per hectare for something like a 16% improvement in the time it takes for your plants to wilt without water, and paper stresses in great detail how the ultimate results achieved in terms of plant available water holding capacity are highly dependent on a wide variety of variables. I suspect that even the paper's upper range estimate of $584 per tonne is too low when transport and incorporation costs are taken into account, plus the fact that the biochar needs to be specifically formulated to achieve results. In what agricultural-financial scenario is an improvement on the order of 16% worth such a high investment cost? In what scenario could the money be raised for such a marginal improvement, well beyond the collateral value of the land itself? 


In the developed world, farmers would invest in crop insurance in case of drought leading to crop failure, and it would be vastly cheaper, plus it would offer a 100% guarantee, rather than buying an extra few hours or days of time before the crop is lost. In the developing world, the amount of labor required to produce and add these quantities of biochar to cropland would be prohibitive, unless it would be for only a small garden plot.


While there may be agricultural scenarios where such a high biochar investment cost could be financially worthwhile, it will not be for water retention. Irrigation systems will be used in such scenarios to ensure plants or trees have sufficient water. In other words, a tomato grower will not invest in biochar to avoid investing in an irrigation system.


To state it plainly, in real world application, biochar should be optimized for financially viable scenarios (which may include sweat equity - labor - in some cases). To the extent that biochar improves plant available water holding capacity in such a scenario, that's fine, but the cart simply won't travel anywhere placed in front of the horse of financial viability.




On Mon, Apr 20, 2020 at 8:13 AM d.michael.shafer@... <d.michael.shafer@...> wrote:

A recent, now quieted down, thread asked about particle size and utility in soil. Attached is the PDF of a paper recently completed by a Ph.D. student working on particle size and water retention, a big issue for many of us working in Africa. Counter-intuitively, she finds that the smaller particles display "hydro-phobia" and retain much less water. She is the lead and corresponding author. Very smart and very articulate. if you have questions, i would just contact her.


Nando Breiter
CarbonZero Sagl
Astano, Switzerland

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