Monday, January 21, 2008

Synthetic fertiliser

All-purpose fertiliser with part of our vegie garden in the background

I've often wondered how this could be. Fertilisers are used to boost levels of nitrogen, phosphorous, potassium and various trace elements in the soil. Crude oil hardly seems like a good source of any of these - the air (for the nitrogen) and rocks seemed to make much more sense.

The answer is hydrogen. The nitrogen in fertiliser is generally present as urea. This is made from ammonia, which in turn is made from nitrogen and hydrogen gas. The nitrogen is purified out of the air (air being about 70% nitrogen anyway), and the hydrogen is made from fossil fuels using the steam reforming process. You see, we currently know of two ways to make hydrogen on an industrial scale - steam reforming and electrolysis of water. Steam reforming does use precious hydrocarbons, but it also uses much less energy than hydrolysis and so is much more widely used. [Which makes me wonder still more about hydrogen cars, but that's another story...]

I know that many environmentalists are in favour of organic agriculture, but I am definitely in favour of synthetic fertilisers. I think that they are much more benign than synthetic pesticides, which are responsible for untold thousands of deaths in India alone each year, but they can still poison waterways if overused. We use very little synthetic fertiliser in our garden at home, prefering our own compost and "blood and bone" fertiliser, but we do not depend on our garden for either our food or our livelihood.

If all of the world's food was grown using permaculture methods then much of our modern lifestyle would have to be given up - far more people would need to be involved in food production than is currently the case, so far fewer people would be available to work in manufacturing, IT, the sciences etc.

In addition, commercial agriculture by definition depletes the soil. On a domestic scale we can grow a cabbage, throw the inedible bits into the compost, eat the cabbage, collect our bodily wastes and compost them then put all the compost back in the vegie bed. (We don't, but we could!) The cycle is closed, and no nutrients are lost from the soil. All that is permanently extracted is the solar energy the plants gather (even the minerals in our own bodies could theoretically be returned to the soil at the end of our lives via. composting or scattering of ashes). It is, however, hard to imagine a commercial farm that could similarly collect its fair share of its customers' excretions and compost them, no matter how close to its client base it was situated.

On balance, I'm happy to live in a world with synthetic fertilisers, especially if care is taken to prevent their run-off and if all available waste biomass is worked back into the soil on the farms.

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