This is a transcript of a speech I gave in December 2012.
Soil is amazing so look after it!
Fellow members and honoured guests, I introduce my speech tonight on the topic of soil
Soil is amazing. Soil is life for the vast majority of the population on earth. Eskimos and space station residents aside. We even named the planet after it. Without soil, we have no means to produce food.
What is soil?
All soil comes from rock. Weathering of the rock is the first step in the process of soil formation. Cooling and heating leads to contraction and expansion within the rock which causes the rocks to crack. The rain then erodes the rock to soil.
The nature of the parent material determines the nature of the soil. Soil derived from sandstone is naturally infertile and tends toward the acidic. The soil around volcanoes is really fertile as it comes from volcanic ash which is very fine and contains minerals and trace elements that plants like.
Soil takes many many years to form. A 2.5 cm layer of soil takes between 800 and 1,000 years to form. So as humans, we treat it with a remarkable complacency.
Any gardeners among us know that to improve the soil, you can add things to the soil. In nature too, vegetation and living organisms influence the condition of the soil. Earthworms and termites are good for the soil as they assist with the decomposition of minerals and matter. Trees are fantastically good for soil – they do many marvelous things including binding the soil together to improve its structure, some trees can be used to fix nitrogen back into the soil and they also prevent soil erosion. Leaves from trees also provide organic matter which benefits soil. I am a big fan of trees and I will tell you more about them in another talk.
What does soil do?
Plants use soil as a nutrient source, as a water store and as anchorage into which their roots grow. Simple as that.
Dangers to soil
One of the biggest dangers to soil is rain –heavy rain at a rate of 10mm per hour. If you have never experienced tropical rain, I can highly recommend it as an equally thrilling and terrifying experience. My first taste of rain in Africa was in a tent in the bush in Nigeria and the rain pours down. Think the worst rain you have ever experienced in the UK and double it – the main difference being that the rain in Africa is warm and evapourates very quickly in the heat afterwards.
The removal of topsoil by rain and wind is called erosion. In the tropics, as much as 250 tonnes of soil can be lost per hectare per year through erosion on badly managed land. A hectare is an area of land measuring 100m x 100m. The central bit of Trafalgar Square is approximately a hectare.
The main causes of erosion are:
Overgrazing –this is where the natural vegetation is eaten by animals to the extent that the soil is left bare. Deforestation is a word most of us are familiar with – where the land is cleared of trees to create space for commercial farming. This also causes erosion as any where the vegetation is stripped back to soil means the elements can wash or blow it away.
Over use of cultivation equipment also causes erosion. Anything that exposes the soils to the elements causes erosion. So looking at the beautifully ploughed fields on your way to work tomorrow morning – they are not good for the soil at all.
This is a bit of a problem as our traditional farming practice has always been to clear the land and plant the crop. In the UK, the fields are so tiny and the weather is fairly benign here so soil conservation is not taken seriously. The average farm size in the UK is 57Ha and 20Ha in Europe. – in the USA and Russia, the commercial agriculture is much bigger scale and the same with Africa. The commercial farms I have visited in Africa have not been smaller than 2,000ha.
In the USA, the mid west was turned into a dust bowl in the 1920’s due to all the soil blowing away following years of over cultivation and poor management so soil conservation is vital especially over large areas.
So how to conserve soil.
Plant cover crops and intercrop between the main crop.
Vegetation helps prevent soil erosion by intercepting the rain fall and dissipating the impact of the rain drops. It prevents surface run off which can wash the soil away. Vegetation helps with the soil structure which encourages greater rain infiltration and reduces the run off.
Design your field plans properly allowing for natural wind breaks and shape field edges to reduce erosion/run off
Plant trees to act as windbreaks around your fields. – also the roots will improve soil structure
Consider moving to no-till techniques. This is where you use specially designed implements that enable you to plant or drill straight through the indigenous grass so you don’t disturb the soil. The downsides to this are expensive implements and extensive use of herbicide to control weeds.
It is not a subject that many of us even think about. We are starting to care a bit more about food welfare for livestock and fish. Do you buy responsibly sourced fish? Are your eggs free range and your bacon Gloucester Old spot? Soil gets no press at all. There have been no high profile campaigns or champions of dirt. Yet it is a huge issue that should concern us all.
Jared Diamond has written a book called “Collapse” which is a very interesting read. Whole societies have failed as a result of mismanagement of soil so you need to value the dirt in your garden, it is much more precious that you think.