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Soil management

Watch Dr Martin Lukac explain why healthy soil is important for crop production.
[SOUND OF BIRDS CHIRPING] Hello. My name is Martin Lukac. I work at the University of Reading. There are two important things that one needs to create a good wine. One is this is a suitable climate, and the other one, equally important, is good soil. We as humans need the soil to grow plants, to grow crops, so that we can feed ourselves. I’m standing in Cornwall, in the west of England, and most of the soils in this place have been created by forests which established themselves past the last glaciation. Once people turned up in Britain and started clearing the forest for agriculture, they removed the biggest engine for the creation of organic matter we have.
Any other form of vegetation, other than a forest, creates organic matter– all the same– but it’s far less than the forest would. We need organic matter in the soil for the soil to function properly. So what happens is once you remove the forest and you start using the soil for agriculture to grow crops, you start losing carbon from the soil, which inevitably means losing soil function. There are several processes which contribute to this soil function. This will be the provision of nutrients. This will be the provision of water. It will be the capability of plants to root themselves and hold themselves in place.
There is also a variety of organisms in the soil, which inhabit the soil and which contribute to cycling of nutrients and water within the soil. There is a host of pathogens which attack plant roots. And there are a lot of organisms which contribute to plants’ defence against these pathogens. Soils in this location, where I’m standing, have been used for agriculture for the past 3, or 4, or perhaps 5,000 years. As long as we keep on doing this, we keep on depleting the soil of carbon and of nutrients. And there are two options we have to reverse this trend.
The first option, which is keep on using fertilisers to maintain fertility of the soil, means mining the fertilisers somewhere on earth, and means using energy to create the fertiliser and ship it around the planet. This means we need to use energy. And since most of our energy comes from fossil fuels, this then means carbon dioxide emissions. The second option, which is increasing the amount of carbon and the amount of organic matter in the soil, is a lot more appealing from the environmental point of view. The best way to achieve this would be to grow forests again. But this is not possible in every location, because we still need the fields to grow crops to feed ourselves.
But even if we keep on growing crops, there are several options available to farmers which they can use to increase the amount of carbon in the soil. One such option is to decrease the amount of ploughing that the farmer does. Every time you plough a field, you lose some of the carbon. Another option is to limit the amount of time when we have just bare soil, because that means there’s no carbon coming in from the plants into the soil. There is an additional problem with having bare soil on your field. This is connected to erosion. As soon as we remove plants, we remove their root systems, which are very good at keeping the soil in place.
So as soon as we cut the plants and we just establish a bare field, any rainfall causes loss of soil from that field. And this then takes thousands of years to get replenished. For example, in the vineyard behind me, you can see rows of crops. And you can also see the interrows, where no crop is grown. But the soil is not bare. There is grass cover. This is in place to keep the soil from moving down the slope. With regards to using artificial fertilisers, we are now at a point where we can optimise their use. We can follow crop development through time, and we can estimate how many nutrients the plant needs at any one time.
So then the farmer can apply the right nutrients at the right time, making sure they are all taken up by the crop, and there is no waste coming out of the field. As I have tried to explain in this short video, soils are of crucial importance for our ability to feed ourselves. It takes thousands and thousands of years to get the soil developed to the point where it can be used for crop production. It is therefore very important to take care of this soil and to make sure it will continue fulfilling its crop production function into the future.
One of the best ways to achieve this is to put carbon in the soil to increase the amount of organic carbon in the soil. And there is a further bonus in this equation in that the carbon that we put in the soil comes from the atmosphere. So we can use our soils to act as a storage of carbon that would otherwise be warming up the planet.
Vines can grow and produce good grapes on comparably poor soils, but for most other crops the quality of the soil is one of their main determinants for a good yield. In this video Dr Martin Lukac explains why a healthy soil is so important for many crops.

Martin mentions how carbon from the atmosphere can be stored in the soil, which is illustrated by this picture of the carbon cycle below. Living plants use CO2 from the atmosphere to form carbohydrates by photosynthesis. Decaying plant material increases the amount of organic matter in the soil, enabling a variety of organisms to thrive and form and ecosystem that supports plant growth. Crops also transform CO2 into carbohydrates, but as they are continually harvested, only little plant material goes back to the soil and the amount of organic matter is reduced over time. Tillage and the application of fertiliser help to increase crop yield, but they don’t increase organic matter in the soil. In the long run, a low organic matter content in the soil decreases soil health and ultimately its productivity.

This image provides a summary of the information in the preceding paragraph. It shows plants growing in the soil in full leaf with roots extending down into the soil surrounded by decaying material, organic matter which provide nutrients. Above the soil the plant is exposed to sunlight and the diagram includes arrows to show the plant absorbing carbon dioxide from the atmosphere. It also shows plants being harvested and the ground being fertilised.

Figure 1: Carbon Cycle (Click to expand) © University of Reading

Were you aware what precious resource soil is and how long it takes to develop? Let us know your thoughts in the comment area below. Remember you can ‘like’ and reply to comments made by your fellow learners.

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