Paul Carson wrote:... looking to start a few new garden beds in the spring, and want to incorporate biochar into them as an experiment. I've been doing research, but I'd like to hear your firsthand accounts. What would you recommend as a good ratio of char to soil? Did you inoculate it first, or use it as is? And finally.. what were your results? Thanks for the wisdom.
Since you (thankfully!) don't mention complicating considerations like soil type, regional climate, plants involved, biochar source, limits on biochar availability, reliance on compost and cover crops, supplemental irrigation/grey water system if any, we can keep this pretty simple. Common advise for a first time application is to apply 5-10% by volume worked into the soil on 5" soil depth basis prior to planting.
I suggest you first do a container study or limited plot study with your garden soil. Classic is 0%, 5%, 10% by volume the biochar. Add a 50% test if you can work it in. I routinely use 50% by volume simple biochar (freshly made, odor free, non-oily, low
ash, low bulk density, woody biomass, high temperature, low volatile matter, 1/4" max size) in my
soil blocks for starting plants. The mix is richly inoculated and charged. Works very well.
You do these 0-5%-10%-50% rate studies to assure you not are grossly mismatching your biochar to your garden ecosystem. Rather than go down the list of often obvious, often classic mistakes, just grow something and revel in the feedback. The 50% by vloume rate can give you a clue what too much biochar looks like.
Plant a legume (beans or peas. look for a sometimes dramatic increase in nodulation) and plant some other favorites garden plant varieties you are familiar with. I use tat soi, basil, summer squash, kale - they seem to respond to biochar in my soil. In my experience, the first noticible effect as biochar test rates increase are typically 1) better germination, and 2) more / earlier rooting. Other effects to look for are thicker stems, and increased drought resistance from improved water holding capacity. Another effect I commonlty see is that when the soil surface remains intact through a moist period, there is indigenous biology on the surface. Also commonly observed are improved soil aggregation, more vitality in the soil odor, and it is easier to wriggle your fingers into the soil.
Use this container/plot observations to derive a volume rate for use in your garden. Many of us use a 5" basis. Biochar a 1/2 inch deep incoporated to 5" is 10% by volume.
In my experience, you can see germination and earlier rooting andnodulation effects at rates lower than ones which get you a noticeably visible improvement in yield. Yield effects are better evaluated by measuring harvest. Your abilities may be better than mine, but I find that an increase in yield is invisible to me util it pushes 50% The biochar plot study I participated in this spring (
AgEnergy Solutions barley stubble gasifier biochar,
Biochar Supreme woody proprietary process biochar) both biochars had a 30-50% increase in spring wheat yield (33 - 38 bushels, up from 26 bushels) at 3200 lbs/acre biochar or about 2% by volume (5" soil depth basis). I could not see the improved yield by looking for differences in the standing grain plot by plot.
We think our wheat plot results speak to the low pH of the soils (big problem in the Palouse, where 100K acres have been acidified by ammonia base fertilizer use) and better water handling capability in a drought year. We applied the biochar later than planned, only a few hours before the spring wheat was seeded, and we expected _no_ results since the seed was placed below the biochar, and no rains showed up to wet the upper soil, kick in the biology, or attract rooting above the planting depth. Yet something positive clearly happened as a result of adding the biochar.
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