Planetary Boundary 3 – Erosion

On a planetary scale we lose soil fertility, and this is a threat to our civilization.

What is a “Planetary Boundary” and why is it important? Link to the introduction article on this topic. The “Planetary Boundaries” is a model of global biophysical systems that support our life on the planet. For each system, quantitative models and indicator metrics have been developed to indicate the health of the system.

Updated levels of the “Planetary Boundaries”, Science 2015.

The third planetary boundary that our civilization has crossed into the catastrophe zone is Erosion, also known as “Land Use Change”. When forests are cut down and plowed to plant corn, the organic matter in the soil – the soil carbons – gas out as CO2 or is washed away with rains and wind, and finally disappear. The effect is that soils can hold less water and the consequence is flooding and slow desertification. We have lost incredible 133 billion tons organic matter in the agricultural soils since the dawn of agriculture. And there is not much left… (This kind of agriculture is therefore a kind of mining.)

Indicator

The indicator chosen is how much of the total ice-free land mass of the planet that is converted to farming (in %)

1. Pre-industrial value: <1 %
2. Current value:   13%
3. Safe zone boundary:  5%
4. Catastrophe boundary:  15%

We are therefore approaching the catastrophe zone for this biophysical system, and with the current speed of cutting forests, we will reach the catastrophe limit around 2050.

Effect

Erosion as a killer of civilization is a well documented companion throughout human history, usually accompanied with the spread of the plow.

Plowed grain culture of barley and wheat was developed in Egypt, on the fertile Nile flood plains, which got seasonal replenishment of fertility. That is in principle a sustainable system that could continue throughout the millennia.

However, as soon as the plow as used on other soils, where there was no replenishment, the soils would slowly lose fertility. With oxen-drawn plows, this was a slow process. We have mechanized with diesel-drawn megaplows, and increased the destruction of soil life by application of pesticides. What earlier took a century can now be accomplished in a decade!

Nebuchadnezzar’s palace in Babylon – home of the hanging gardens in those days. Now semi-desert. Photo BBC World.

 

Dunhuang, Gansu, China, was a very prosperous city on the Silk Road. 1500 years ago, it was the capital of the Western Liang country, and had more inhabitants than Rome. Actually more than any city in Europe. Now surrounded by desert.

 

Mechanism

The soil is turned upside down by the plow, which makes organic matter break down faster. This is advantageous for the farmer, since it kills weeds and makes plant-available compost.

Modern tilling. Image wikipedia.

However, there are three problematic effects:

1. Soil organisms die and release CO2: The disadvantage is that soil organisms like mycorhiza fungi also die when exposed to the UV rays of sunlight and gas off as CO2. The soil also loses the sponginess called “tilth”.

2. When the tilth is lost, and the mycorhiza fungi die, the soil organic matter is no longer held into the soil, but can wash away with rain drops that have direct access  due to the turned-over soil. This is why the Yellow River in China is yellow – the tilled Löss-plains release the fine organic matter and clay particles, which clog the river downstream.

You can see an example in this aerial photo of the city of Passau, where two rivers come together:

Passau, where the left river comes from an agricultural area, the right river from the forests. Image Wikipedia.

3.  Compaction blocking water flow:
There is compaction in the soil just beneath the reach of the plow, which blocks water percolation.

Compaction as a consequence of plowing (left). Image from Ontario Ministry of Agriculture.

Solutions

There are ways to grow food without killing the soil. The best way is to use trees and other perennial plants, and avoid pesticide applications.

Here is a beautiful video of a project that was done in Deng Xiaoping’s China in the 1990’s, Green Gold by John D. Liu.

Here is an amazing book by the American researcher J. Russel Smith, who proposed “Tree Crops” already in 1929!

Sweet chestnuts are an amazing tree crop. Healthy and delicious!

What can I do?

• Eat more from trees! Nuts, fruit and vegetables from trees help rebuild soils and stabilize the land. Choose walnuts instead of bacon, avocado instead of yoghurt. Chestnuts instead of potatoes.
• Eat less meat. Buy organic grass fed meat. If you can from a farmer you know.
• Join a political party and push for a transition to organic no-till farming. No-till means keeping the plow out of the ground.
• Plant a fruit-tree in your yard, in your park or on a nearby schoolyard.
• Get the book “The Carbon Farming Solution” by Eric Toensmeier with plenty of exciting tree crops!

Get your own copy of this excellent book at Chelseagreen,com or your favourite bookstore.