Soil amendment

Bear Kaufmann. Initially posted April 7, 2008. Updated August 5, 2008.

Images showing trial preparation and radish germination
(Select image to enlarge in Gallery.)

Materials/Methods

Char was Lazzari Brand mesquite BBQ char (due to availability), crushed and screened to 1/8".
No nutrients were added to the char itself or to the soil.
Soil was FoxFarm OceanForest Potting Soil.
Sand used was horticultural sand.
No mycorrhizal fungi were added.
Mixtures range from 0-100% sand, soil, and char in ~16% increments by volume. 90 pots total. 28 combinations with 3 pots each + 6 additional pots at 33%/33%/33% composition. Pots were placed randomly within the tray. Tray was rotated 180° occasionally.
Plants were watered daily by a drip irrigation system.
Plants were removed from pots ~1 month after first watering. Soil was rinsed from roots and roots were patted dry with a towel. Wet weight of roots+shoots was measured (Acculab VI-3mg, 0.001 g precision).

Figure 1. Box Plots Showing Effect of Composition Across Three Transects

Figure 2. Pictures of Radishes at Important Compositions

Results

Plant growth was stunted even for the best preforming plants, likely due to the small pot size. Leaf color varied across different compositions.
A mixture of 33% charcoal and 67% soil had the best growth (176% of pure soil). Aside from mixtures around this level (Figure 1b), high levels of charcoal showed a generally negative effect on plant growth (Figure 1c).

Discussion

The positive interaction effects of charcoal and soil (Figure 1a,1b) are interesting. Assuming charcoal itself provides no integral nutrients to the soil (eg. nitrogen), increasing amounts of charcoal reduce nutrients available from the soil mixture. The effects at 33% char/67% soil, however, show beneficial effects. This could be explained by increased mineralization rates caused by the charcoal causing soil nutrients to be more available to plants. Beyond 33%, the Cation Exchange Capacity of the charcoal may have held the nutrients produced by mineralization, making them less plant available. Since the charcoal was not amended/soaked in a nutrient bearing solution it likely had a low Base Saturation leading to adsorption of nutrients as they became available. Other potential explanations for increased growth along the soil/char transect include alterations to pH or limiting nutrients (eg potassium(?)) provided by the charcoal. The speculative mineralization/CECi model could also explain the effects seen along the sand/char transect. Here, since the sand lacks organic materials and bound nutrients for soil microorganisms to make plant available, the increasing unsaturated CEC may have made any nutrients less plant available.

Author: Bear Kaufmann bear@ursine-design.com

Charcoal as Soil Conditioner: Studies in the humid Tropics
Christoph Steiner1, W. G. Teixeira2, J. Lehmann3and W. Zech1, U Georgia TP 2004

Learning to use wood charcoal in farming at a Northwestern Washington native plant nursery.
Richard Haard, Fourth Corner Nurseries, Washington, Febuary 20, 2007
My motivation for preparing this post is to be able to use this motivate discussion of charcoal as a soil additive. Trying to do this work at a very busy nursery that is perhaps pushing their production factor too high (over 80%) is rather frustrating as experiments have gotten over ruled by planning changes, wiped out by harvest before I can read the data and the conditions set up for the experiment just do not work. However, I have been encouraged however and I am now using hardwood charcoal as a carrier for natural inocculum as a matter of routine.
Fourth Corner Nurseries is a wholesale supplier of native plant species, located on 77 acres in the coastal lowlands of northwestern Washington, USA. With approximately 40 acres under cultivation, we produce two/three million direct-seeded, field-grown, bare-root native plants annually. Our principal crop is individually seed-sourced, bare-root deciduous trees and shrubs, herbaceous perennials, grasses and emergent species such as sedges, cattails and rushes for environmental restoration purposes. Our mission is to sustainably grow plants while supporting workers and their families who depend on the farm for their economic subsistence. Use of surplus biomass from our willow coppice field and other materials is our alternative energy vision.
Aerial view of our farm

Where can you get Cheap Natural Fertilizers and Soil Amendments?
David Hall, iVillage GardenWeb

One of our composting experts and friends on this site, David Hall (DcHall_San_Antonio), recently gave a great list of some of the major benefits from soil high in organic matter:
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Charcoal as Soil Conditioner Studies in the humid Tropics
Christoph Steiner1, W. G. Teixeira2, J. Lehmann3and W. Zech1

1Institute of Soil Science, University of Bayreuth, Germany
2EmbrapaAmazoniaOcidental, Manaus, Brazil
3 Department of Crop and Soil Sciences, Cornell University, USA

Use of Murayoshi Bincho Charcoal for Flowerbeds and Fields
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Murayoshi Bincho Products

The History of Bincho Charcoal

Black Carbon from Rice Residues as Soil Amendment and for Carbon Sequestration
Stephan M. Haefele 1, J.K. Ladha 1, and Yothin Konboon 2.
(1) International Rice Research Institute, Los Banos, 4031 Laguna, Philippines, (2) Ubon Rice Research Center, Ubon Ratchathani, Thailand
18th World Congress of Soil Science, July 9-15, 2006 - Philadelphia, Pennsylvania, USA

On highly weathered soils in tropical and subtropical climates, maintenance of soil organic matter is essential to sustain system productivity and avoid rapid soil degradation. But climatic conditions as well as soil characteristics favor the rapid decomposition of organic matter. However, several recent studies indicated that black carbon, the product of incomplete combustion of organic material, could combine characteristics highly beneficial for soil nutrient dynamics with high stability against chemical and microbial breakdown. Lasting soil amelioration by incorporation of black carbon from wooden plants was proposed based on the beneficial evidence from “Terra Preta” soils in Western Amazonia. Theoretically, charred crop residues in rice-based systems could serve the same purpose but this hypothesis has never been tested. Within this context, our objectives were to 1) assess possible options for the use of charred rice residues, to 2) test the effect of charred rice residues on important soil fertility parameters and rice growth, and 3) to evaluate the effect and stability of charred rice residues in a variety of rice growing environments.

Black Carbon from Rice Residues as Soil Amendment and for Carbon Sequestration
Haefele, SM, Konboon, Y, Knoblauch, C, Koyama, S, Gummert, M, Ladha, JK
Cornell University Poster Presented to International Rice Research Institute, September 14 2006

On highly weathered soils in tropical and subtropical climates, maintenance of soil organic matter is essential to sustain system productivity and avoid rapid soil degradation. But climatic conditions as well as soil characteristics favor the rapid decomposition of organic matter. However, several recent studies indicated that black carbon, the product of incomplete combustion of organic material, could combine characteristics highly beneficial for soil nutrient dynamics with high stability against chemical and microbial breakdown.