Diagram labelling

LecturerWelcome to this talk on soil science and organic farming. Dirt, soil, earth, loam, mud or dust: it doesn't matter what you call it, it is of primary importance in the production of food and other crops. Most people think of it just as a medium in which plants grow, but it's more than that. It's actually a living entity, or it should be if it's healthy, and human health is affected by the health of the soil.

LecturerHealthy, living soil is literally crawling with life. There are the obvious earthworms, which burrow in the soil and help to aerate and improve it, beetles and other hard-backed insects, and various invertebrates like centipedes. Then there are fungi and bacteria, also living forms. Healthy soil needs food, air and water to help plants grow, and the more nutrients in plants, the more are available for humans and livestock. It stands to reason, therefore, that plants grown in poor soil will have few nutrients to pass on to the consumer, whose well-being will be worse off over the long term.

LecturerSo, where do plants get their nourishment? Most of it comes from the soil. Some nutrients are made up of minerals from the earth, while others come from dead plant and animal matter, which is broken down over time by the living insects and other organisms in the soil. Plants depend on these little living creatures to convert minerals and other vital elements into a form that can be taken up by the plants. And it's a synergistic relationship: in turn, the plants help those organisms by releasing sugars and enzymes back into the soil.

LecturerBefore I go any further, let's take a look at the structure of soil. Now, if you look at the diagram, you'll see that soil is made up of many different layers. Let's start at the bottom. This is the bedrock, under all the other layers. The layer above that is called regolith. Here the bedrock is slightly broken up, but plant roots don't penetrate this layer. Moving up the chart to the next layer, we come to the subsoil, which contains clay and mineral deposits. On top of that is the eluviation, or leaching, layer. This is quite light in colour and is mostly just sand and silt. As we get near the surface, we find the topsoil. You will hear a lot of talk about topsoil amongst farmers. It's the most important layer of all, because it's where seeds germinate and roots grow. Now, at the top of the chart, you will see a comparatively thin layer. This is organic matter that is still in the process of decomposition. It mostly consists of leaf litter and humus. Just think of the surface of the forest floor: partly decayed leaves and twigs, that sort of thing.

LecturerAs you can imagine, good soil forms very slowly over time, but it can be lost very rapidly through erosion. In addition, soil quality can be affected by pollution, from anything from industrial waste to the artificial fertilisers used by conventional farmers, which have been shown to suppress the diverse life forms in the soil. This is why organic agriculture is the way of the future.

LecturerLet's take a quick look at the conventional system, which is often based on monoculture, the production of a single large crop. It relies on chemicals for fertiliser and pest control. It is also becoming an increasingly common practice to use genetically engineered seeds. And more chemicals are used to control insects and fungi which attack crops in storage and during transportation. Also, did you know that there is no requirement for conventional growers to keep records of their production practices?

LecturerOrganic growers, on the other hand, choose the most environmentally friendly options for dealing with pests and disease, working towards prevention in the first place. Some of the strategies they use include alternating the crops grown in each field. Because different plants add different nutrients to the soil, by rotating crops, the soil is naturally replenished. Surrounding crops with green waste can not only conserve moisture in the soil, but it can also prevent weeds from springing up, and it feeds the beneficial micro-organisms. Organic farmers often release beneficial insects as predators, which removes the need for artificial pesticides. Animal manure combined with green waste, correctly composted, fertilises the soil in a way that encourages life rather than suppressing it.

LecturerTo sum up, organic farming is the only sustainable way of feeding the people on this planet and keeping both the planet and the people in good health.