Sunday 12 April 2015


How can humanity screw-up the environment?  Let me count the ways!
What we tend to get exercised about is the discharge of mercury salts into the sea-water at Minimata, or the plume of dioxins that covered Northern Italy when the factory in Seveso blew off 6 tonnes of toxic chemicals. Actually you don't get exercised [how quickly they forget] about such things unless you are my age or older.  People ten years younger will still feel a frisson on hearing Bhopal. The list goes on because mistakes are made, but these are all point sources of pollution. More damaging overall and certainly more insidious are the diffuse, generalised sources of bad practice and ignorance which take a toll on the invisible parts of the environment.

They say that we know more about the far side of the moon than about the abyssal ocean.  If that is true it's partly because the moon is without life and so much simpler to understand than any part of the world which is teeming with a wild diversity of living things.  You can find life even in such inhospitable places as hot springs loaded with sulphur and the white smoker hydrothermal vents at the bottom of the sea where the temperature and pressure should make life insupportable. You wouldn't think that the soil, which we've been running through our fingers for a million years, was similarly closed off to our understanding.  But mental as well as physical inaccessibility can close off avenues of investigation. We take soil for granted and I suspect that the primary mental image is that it is an inert vehicle that supports our bean-poles.  Yes, yes, we do know about Rhizobium meliloti and its relatives: bacteria that inhabit the root nodules of beans and other legumes and fix nitrogen for them.  And since Darwin wrote The Formation of Vegetable Mould through the Action of Worms, with Observations on their Habits (1881), we have realised that worms do something positive for the soil and shouldn't be casually chopped in half with a spade.  But we haven't begun to appreciate the diversity, let alone the delicacy of the soil as a community.

One notable way in which we can tilt soil quality in disastrous directions is to apply nitrogen fertilisers which gives an unfair advantage to bacteria that eat their fixed nitrogen over the bacteria that, at enormous cost, make it. One of the slides I show in my lectures about the nitrogen cycle is a patch of soil half covered in clover: that area has been seeded with minute quantities of the element molybdenum which is an essential ingredient of the enzyme nitrogenase which fixes nitrogen from the air.  The soil in the picture has been depleted of the element through millions of years of leaching and erosion. We have no idea what effect the loss of nitrogenase bacteria has on the long-term health of the soil, on carbon utilisation, on water-retention, on the mobilisation of trace elements.  It takes Irish schoolgirls to make a crucial step towards understanding the complexity of roles played by nitrogen-fixing bacteria.

There was an interesting piece in Nature 15th Jan 2015 all about biochar.  It's more or less what it says on the tin = charcoal; and its marketing has a sense of cure-all about it.  It improves the drainage of both sandy and clay soils by having particles that are different in shape and size to whatever medium it is added.  And there are also complex interior pathways in charcoal which make neat and cosy habitats for the microbial community.  But even here, all is not equivalent: it seems that biochar from rice-straw doesn't have the same productivity enhancing qualities as biochar from wood.  That is not so surprising maybe,  rice has shallow roots so it is not adding anything to the top soil merely re-churning it.  Wood on the other hand will have brought micro-nutrients and minerals up from the subsoil: charcoal is plainly not 100% carbon and a trace of molybdenum might make the difference.

You can buy biochar on amazon: it's more expensive than pork chops, even before you factor in postage&packing. If biochar is going to be the latest hot thang in gardening, the planet is going to take another hit as forests are felled to be doled out in trowelfuls into suburban allotments and rose-gardens.  We have a wood-burning stove that has heated the living room for the last 17 winters only from what falls out of the ditches during storms.  I sieve the wood ash and periodically spread it out to 'sweeten' the acid soil in the the fields when there is a gentle breeze.  The remaining charcoal has been bagged to start barbecues, which we but rarely entertain.  I'm going to re-label these bags BioChar €5.99/kg and dig the contents into the bean beds.


  1. Hi Bob, I'm looking forward to reading more!

  2. Cool, and welcome. I promise to write about Canada so you can say "Rubbish!!"