[Terrapreta] charcoal in soil experiments

[Richard Haard]

Discussion group -


Very good discourse on experiments with charcoal in agriculture. For  
your reading interest, this is the point I am at in my own container  
testing project at 4CN. Comments and suggestions are always welcome.

My own experimental setup is scheduled to be launched by end of month  
at latest. I have already started my test subjects in 4x4 containers  
and their roots/shoots should be active when I start.

This weekend I am laying out  and calibrating my irrigation system  
and I will be using the same rate of watering as our seedbeds in the  
adjacent fields. We will have tensometers in place to be sure we only  
water when needed. Dr Steiners comments are very interesting and  
helpful at this point as I need to decide on rate of charcoal use in  
the pots. I am planning to use charcoal at a high rate because this  
is a screening for effect and not a dose related study. Present plan  
is to use 30% on v/v basis but am interested to see what this  
discussion reveals.

  Another factor I will need to mitigate is pH changes brought about  
by the charcoal. Our farm soil is running pH of 6.6 and need to keep  
everything at this level or below. I noticed in the Georgia master  
gardeners study they used sulphur to adjust pH downwards and am  
thinking I may need to do this too.

The soil at our farm is a different chemical profile from that  
mentioned  by Christoph in Brazil. We have a sandy loam that is  
highly leached, has medium to medium low phosphorus, very high  
potassium (probably due to glacial origin as unfarmed soil nearby is  
same), very high calcium, medium magnesium, low or nil nitrogen.  
Organic matter is about 4 to 6% or about midrange.  So far as trace  
elements Copper, Boron ,Manganese, Iron and Zinc are at the low end  
of the range. Our fertilizer mix is formulated to match these special  
trace element needs as well as our major element requirements and is  
the same as our farming operation uses.

I am conducting soil tests and foliar analysis this year at the  
University of Mass, soil testing lab.  Their reports come with  
recommendations, are very easy to read and come with a squib to  
explain what each test means. Each test, with organic matter costs $13.

Also interesting to study is the cation exchange capacity and base  
saturation in this soil testing regime. The CEC is a measure of the  
soils ability to retain  and supply nutrients. Our CEC, 11 to 12%  
probably represents our relative low organic matter and content and  
also  % base saturation of  4 +%K, 6-10% Ca, and 48 - 61 % Mg are  
measures of adsorbed cations in our soil.

I will be looking at these data points, especially soil nitrogen in  
my various treatments. Measuring the effect of treatments is always  
troublesome for me and numbers like these will be helpful when I am  
trying to interpret plant yields.

My main interest is to learn if a container test can be useful to  
evaluate our farm soil management practices and therefore am using  
soil that has been cropped in a 2 year cycle and using no fertilizer  
in the control. Normally for a 2 year (2-0) crop we use a single  
treatment of fertilizer in a pre-planting treatment, with sometimes  
compost incorporated. During the growing season we use a light  
treatment with urea to stimulate early summer growth.

What is interesting to me is to see what effect charcoal will have on  
this management regime, not only for a single season but to save the  
soil for another second crop the next season without additional  
supplements.  To take this extended view I figure i need a high  
volume of soil so i am using 4 gallon pots. As these plants are a  
woody shrub and a perennial we will run the test until after killing  
frost.

There will be 300 to 380 pots in my project.

Best

Rich Haard, Fourth Corner Nurseries, Bellingham , Washington