Last week I said I was going to experiment by making a cake I often make at home to go in my lunchbox, the experimental part being that I would be using only the heat of the sun to bake it. In the event I’m pleased to say that it was a success although the day was not as sunny as it might have been so the solar oven only reached about 110° instead of the 150° I had hoped for. As a result I had to guess the timing – if I had opened the solar box to test the cake I would have lost the oven heat, so instead of about 1hr 15minutes as in my electric oven, I left the cake in for over 3 hours and the result was perfectly acceptable although slightly “heavier” than at home.
The recipe is as follows if you wish to try it yourself – very simple and makes a cake which keeps well, freezes well too, and is delicious with butter!
Mix together 4 Weetabix, 1pint milk, 1lb sugar and 1lb mixed dried fruit and leave to soak overnight. Then mix in 2 beaten eggs and 1lb flour and divide between 2 loaf tins. Bake at 150° for about 1hr 15 minutes.
You could try substituting cherries or apricots for the mixed fruit – as the mangoes are nearly ready I will be trying them in the next mix.
One of the regular jobs at MyFarm is the production of biochar – charcoal used as a soil conditioner and fertiliser. Production is based on a process which has been recorded as having been carried out thousands of years ago in the Amazon Basin, where islands of rich, fertile soils called terra preta (“dark earth”) were created by indigenous people. Anthropologists speculate that cooking fires and kitchen middens along with deliberate placing of charcoal in soil resulted in soils with high fertility and carbon content, often containing shards of broken pottery. These soils continue to “hold” carbon today and remain so nutrient rich that in parts of Brazil they have been dug up and sold as potting soil. This carbon resists degradation in soils for thousands of years and is found in soils around the world where it helps depleted soils retain water and nutrients. By making farm land more fertile for longer it helps discourage deforestation and can improve soil fertility, stimulating plant growth, which then consumes more CO2 in a positive feedback effect.
Biochar is fine grained and extremely porous with a large surface area which is very effective at retaining water and water soluble nutrients and is produced by heating agricultural waste in a low oxygen environment to prevent combustion. At MyFarm the process is a fairly low tech and time consuming operation using a simple kiln made from an oil drum. Dry twigs and other garden waste is broken or cut into small lengths and packed tightly inside a metal drum until the drum is full, at which point it is turned upside down inside a slightly larger drum.
The space in between the two drums is now packed with more twigs for fuel topped off by a layer of mango leaves which are lit and the kiln is closed with a chimney funnel. The smoke from the chimney normally soon disappears to be replaced by flame and hot exhaust gas which in a more sophisticated system might be used to generate electricity. From experience it seems we get best results if all the contents are of a similar size and our small kiln takes 20 – 30 minutes before pyrolisis is complete.
At this stage the chimney is removed from the kiln and water is poured on to douse any remaining fire before the contents are tipped out and pounded to a powder to be incorporated in the seedbed. This soil conditioner will not only help to retain water but will also add potash and help increase the pH of the soil.
Other benefits of biochar appear to include
Reduced fertilizer inputs: Biochar can reduce the need for chemical fertilizers, resulting in reduced emissions of greenhouse gases from fertilizer manufacture.
Reduced N2O and CH4 emissions: Biochar can reduce emissions of nitrous oxide (N2O) and methane (CH4)—two potent greenhouse gases—from agricultural soils.
Enhanced soil microbial life: Biochar can increase soil microbial life, resulting in more carbon storage in soil.
Reduced emissions from feedstocks: Converting agricultural and forestry waste into biochar can avoid CO2 and CH4 emissions otherwise generated by the natural decomposition or burning of the waste.
Energy generation: The heat energy—and also the bio-oils and synthesis gases—generated during biochar production can be used to displace carbon positive energy from fossil fuels.