Biochar Experiment (2)

The biochar samples arrived from Oxford Biochar (Biochar Experiment). What we are required to do is to grow a crop of our own choice in two adjacent square metres of soil, identical except that one of the two mini-plots has biochar added. Today I have prepared two beds on part of one of my new raised beds and added the biochar to one of them. Although I won't be planting for a few weeks yet, by preparing them now I am giving the biochar a chance to be 'primed' by the soil organisms and the compost that I added (to both plots to maintain equality). Oxford Biochar didn't indicate if their material has gone through any priming process. When I submit my results I'll make sure that I record the length of time the biochar has been in the soil prior to planting. I know from reading about other biochar experiments that sometimes results which show no positive, or even negative results, from biochar application are explained by the fact that 'fresh' biochar has been used.

The application rate recommended by Oxford Biochar is 1.5Kg (the bag you see in the picture) per sq. metre. That is the equivalent of about 6 tonnes to the acre (15 tonnes/hectare)and is at the mid to lower end of recommended agricultural application rates, certainly not excessive.

With reasonable care taken to ensure that the soil and growing conditions of the two plots are comparable, it is reasonable to assume that any significant differences in crops yields will be because of the biochar. However, assuming there is a difference, there remains the problem of identifying which characteristics of biochar are responsible for the variation. In itself it has no nutrient value but one or more of its physical characteristics may increase my yields:

• There could be a rise in PH. This could be marginally helpful for some crops but my PH is generally OK for most things I am likely to grow.
• Biochar can help with drainage on sticky soils but my raised beds are fine in that respect.
• On the other hand they can also help retain moisture. In a dry summer that could be helpful.

You can begin to see how biochar's effect are most pronounced on degraded soil or those which suffer from a particular negative characteristic. On these criteria I can't imagine a dramatic effect but biochar's trump cards are:

• an ability to store nutrients in its maze of microscopic channels
• encouragement of microbial and fungal activity leading to
• increased availabity of Ca, Mg, P, and K

If I do see growth differences in this experiment I expect that it will be these latter characteristics which will be at work. I'll have to wait and see but there is one observable characteristic of biochar which is immediately obvious - the albedo effect. I hope you see in this picture (click to enlarge) how the biochar, although mixed into the soil, has left enough on the surface to darken it. My soil is a dark loam anyway but the additional darkening affect should retain that little bit more heat, valuable at this time of year as the soils struggles to heat up.

Of course there is one more important variable - what to grow! I might try to squeeze as much as possible from the experiment and plant to different veg, perhaps a root crop and something leafy. Carrots and lettuce?