It seems that so much of what we were taught in the 1960s and 70s turns out to have been wrong. This applies to all sorts of things that are now judged differently. British Empire was seen as a wholly good thing bringing education, Christianity, law and agricultural science to a backward world. Now it is described rather differently. Similarly, what I was taught at Ag College was how to use chemicals to control weeds and insects, that we needed to plough to release soil fertility and that we needed bags of NPK fertiliser to grow huge crops. The past 30 years for me has been a slow unlearning of those simplistic ideas. I need to confess my revisionism.
Lets first talk about soil, since it is the basis of all farming. Its simplistic to believe that humans have been ploughing soil for thousands of years. Until the industrial revolution ploughing was shallow and not very inverting, that takes horsepower and steel. So ploughing has only been around for 200 years. It was also part of rotations where fields might have been fallow or grazing for years, allowing the organic matter to rebuild. Even so soil fertility and crop yields were declining across Australia, Canada, UK in late 19th Century as catalogued in the book the Wheat Problem published in 1904. Then Haber invented the process of extracting N from the atmosphere (before inventing poison gas warfare and genocide). So now people talk about how half the world’s population is only fed through the use of chemical fertiliser. This is misleading as about 50% of the world’s food production is never eaten by humans. It rots in poor storage or is fed into bio-ethanol processing or just buried as crop residue or thrown away after being turned into products no-one eats.
The part that was missing from soil science education was the carbon cycle. Every year we harvest carbon in the crop that plants have synthesised from the atmosphere. Ploughing, especially deep ploughing with high powered tractors causes soil carbon to deplete as CO2 to atmosphere. As soil lost its carbon it held less moisture and became compacted, thus needed more tillage to create a seedbed every year. They never taught that we need to apply carbon as well the NPK. Of course in livestock areas slurry and farmyard manure did some replenishment but parts of the world just specialised in cereal production and the results are becoming more obvious every year as erosion, pollution and desertification.
Now I own a field I spend a lot of time and money building up the soil carbon to replenish what has gone missing after decades of extractive agriculture. The top layer of humus is very thin but is rebuilding. We have a composting plant for the city of Exeter just down the road so we only pay for delivery. We are working out how to suppress weeds with competitive plants and shallow hoeing. Now whenever I see someone ploughing I think of as a recreational habbit, a costly hobby that destroys the soil in the long run.
