Earlier this year I blogged on the subject of soil based on an excellent book by that name by Matthew Evans.[i] I said that I would return to the subject and that is what I’m doing.

When humans started farming, we paid more attention to soil than we do today. We could see the results, and feel it in our stomachs, when soil is lacking, as well as when it was doing well. Civilisations have had a nasty habit of turning arable land into desert when they became too big and lost their ability to nurture soil. By the Victorian era a good gardener knew that worms meant lively soil, even if they couldn’t see the tens of billions of microscopic workers that also formed their soil ecosystem. Also, by that stage scientists had worked out that nitrogen is a key macronutrient for plants, making them grow bigger, faster.

There is an essentially unlimited source of nitrogen in the air (the atmosphere is nearly 80% nitrogen), but it’s hard to capture in usable form. Scientists were keen to figure out how to harness atmospheric nitrogen and turn it into reactive nitrogen, both because it could be used as artificial fertiliser, and because reactive nitrogen is great for making bombs. Unfortunately for many, in 1909 a German scientist worked out that an input of mass amounts of energy, at high temperature and pressure, along with a catalyst, could trap atmospheric nitrogen and turn it into ammonia. Only a year later Carl Bosch discovered a way to ramp up production for commercial use, in both bombs and farms. By 1913 the first ammonia factory was up and running. A year later World War I started and with it came the desire for bigger more deadly bombs. The German war machine geared up to turn atmospheric nitrogen into bombs.

After the war, Germany was a broken, impoverished nation that had to rebuild. The ammonia factories became the foundation of the fledgling fertiliser industry. So, despite the fact that this discovery had led to many thousands of deaths it would also lead to the saving of billions of lives as the application of nitrogen synthetically allowed expansion of agriculture into areas previously considered marginal but the introduction of this form of nitrogen leads to a suboptimal subterranean ecosystem. So, while there has been an increase in plant growth there has been a corresponding decrease in the nutritional quality of our food and at an escalating environmental cost.

The second most vital macronutrient for plants is phosphorus. Phosphorous is very effective in enhancing shoot and root growth, as well as other functions like aiding cell division and efficient energy use. Nauru was once a tropical paradise but unfortunately it also had the richest source of phosphorus ever discovered. A combination of Australia, New Zealand and Britain stripped 43 million tonnes of phosphorus-rich earth from Nauru and shipped it off to be used in garden centres, orchards and fertiliser factories all over the world. Today Nauru’s inland is a wasteland poisoned with the heavy metal cadmium. Nauruans have a life expectancy about 20 years shorter than most developed nations, along with particularly high rates of heart disease, diabetes and kidney failure.

An American Norman Borlaug spent all his working life helping poor countries select high yielding crops and plants more resistant to disease. Wheat, one of the three most commonly grown crops on the earth, is a great example. Traditionally wheat was much taller than most of what we grow today but when you add artificial fertiliser to it the plant gets too heavy for its stalk and some stalks bend over. Borlaug’s work in plant breeding, especially dwarfing varieties, increased yields, reduced disease and allowed grain to be grown on impoverished, nitrogen-poor soil. The same principles applied to rice with almost similar levels of success. However, while it is more efficient in a sense producing more yield, the protein content can be substantially lower so you get more calories, less protein. If you change the conditions in soil, you will change the food that the soil grows. So, the very things that Borlaug was doing to increase the amount of food grown – hybrids, plant size, artificial fertilisers – have damaged soil. His work was described as the Green Revolution, but it actually created less greenery on crops and less of the beneficial sugars that greenery produces. It wasn’t just in developing countries that this process took place but also in the rich countries. If we judge the work by the number of calories produced it’s been successful, but it’s come at a cost in terms of nutrient density. Nitrogen in the air is stable, it’s inert. When turned into fertiliser it becomes reactive, meaning it can be changed. It doesn’t just react with the target plants. Nitrogen is leached into waterways, where it becomes a toxin in any quantity. Around the world, vast bodies of water are constantly being poisoned by fertiliser use. The other effect of artificial nitrogen is its role in the atmosphere where it becomes nitrous oxide. That is a very potent greenhouse gas. Depending on where you get your data it is estimated to be about 300 times more warming than carbon dioxide and sits in the atmosphere for centuries.

Much of the increased production of cereal crops weren’t used for humans to eat. In the United States 40% of corn is grown specifically to be turned into ethanol, with the by-product fed to intensively farmed animals. Soybeans are also used to make ethanol and the meal used for livestock fodder.

I suspect that most people think that one of the greatest inventions of the human mind was the plough and that the plough has been of great benefit to humanity. Ploughing land loosened soil, releasing nutrients more readily, especially nitrogen. It lessened weeds, gave furrows – grooves - for sowing seed, and was thought to allow more water infiltration. But actually, it is the plough that has done likely the most damage to our planet. Turning soil has done way more harm than anyone could have imagined. It has unleashed at least a third of the increased carbon dioxide in the atmosphere that has appeared since the Industrial Revolution. It was the single biggest emitter of human-induced carbon into the atmosphere until about the 1950s bigger than coal, bigger than oil.

We are losing soil, on a global scale, on ploughed land, about 100 times faster than it can be made. Wind and water erosion take hold on the ground laid bare by the plough. Colluvial erosion, where loose soil moves downhill due to the action of gravity, also takes place but this we can see for ourselves. What is more difficult is what we cannot see - the soil ecosystem and as we dig we expose that to the air and lots of the microbial community then die. When they die they release carbon. In some cultures there may have been some past understanding of this with crop rotation and need to leave some fields fallow, letting the paddock go back to pasture and allowing animals to graze it. Without realising it they were letting the vast underground community regroup and repair. The advent of the internal combustion engine, cheap fuel, cheaper fertiliser have led to massively increased use of the plough over much more of the Earth’s surface. Continuous ploughing, especially interspersed with sewing a single species of crop, is the best way to mess up soil.

Some farmers have introduced no-till agriculture but this is still damaging and soil is lost up to 20 times faster than it is replaced. We know then that ploughing, adding artificial nitrogen, adding phosphorus are all bad for soil. So too is the rampant use of herbicides and insecticides. Some of these herbicides don’t just kill the weeds that we see but much of the subterranean life we don’t see. Fungicides, widely used to discourage mildew and moulds on crops, can depress those other marvellous fungi that are feeding plants and gluing soil together. Similarly, insecticides are indiscriminate. You may spray an insecticide designed to kill aphids and take out the local bee population at the same time. A whole industry has grown up deploying chemicals in agriculture but 95% of herbicides and over 98% of insecticides are not even reaching the target pest.

The best way for growers to protect soil is to avoid bare earth – whether it’s in your home garden, or on the world’s biggest farm. Don’t dig if you can help it. Ideally, keep continuous, living plant cover if possible, mulch any bare earth, and encourage diversity. The more diverse array of plants you can grow, the more diverse your soil microbes become, and the more resilient your land is.

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