Where the wild weeds are

2015-08-04 11.32.03

Sometimes, as a scientist I am required to communicate my work to a larger audience. Often this can be tricky as it forces me to step outside of the world I frequent on a daily basis where everyone speaks the same language full of scientific jargon. I am forced to reconnect with the real world and translate my work into everyday English; something which is not always an easy task. Here is an overview of my project in what I hope is language that everyone can understand.

 

Farmers in the UK, and around the world, face many challenges. We often hear about problems of insect pests or deadly diseases destroying crops worldwide. But in fact, one of the biggest problems faced by farmers is weed control. When weeds grow in a field they not only take up valuable nutrients and water from the soil but can also compete with crops for light. This means the crop plants may not grow as large as they would do otherwise and so they produce less food.

Black-grass is a grass weed found in cereal crops, like wheat. It is extremely well-known to farmers across the country and in most of England, it is proving especially problematic.

As you walk around the southern and eastern English countryside in the summer you can see this weed growing across almost every wheat field you pass and farmers will be doing everything they can to get rid of it.

There are many ways that farmers are trying to reduce the amount of black-grass in their fields but currently chemical weed killer, or herbicide, is the most preferred. These chemicals can be applied to the bare soil in the autumn to try and prevent the weeds from emerging or they can be applied in the spring before the crop matures to kill off any weeds that have already started to grow.

In most cases a farmer will apply the chemicals uniformly across the whole field. This is nice and simple, you can drive your tractor up and down the field spraying as you go. However, when you are next out walking in the local countryside and you go through a wheat field I want you to take a look around for black-grass. It is usually nice and easy to spot with dark seed heads that stand just a bit taller than the crop.

Hopefully, you will notice something.

The weeds don’t grow uniformly across the field. Instead, they form patches of varying size and shape. This presents an opportunity for farmers to target where they apply their weed killer. Why should we be spraying the whole fields when the weeds are only growing in some parts of it?

These chemicals are expensive to buy and so any reduction in the amount of chemical applied to a field will have a direct financial benefit.

A reduction in the amount of herbicide used will also have environmental benefits by lessening the negative impacts on other organisms in the area – we don’t want to be damaging wild flowers in nearby hedgerows for example or polluting nearby water courses.

It seems simple doesn’t it? Only spray the chemicals where there is a problem with weeds. If you had a skin infection on your hand you wouldn’t expect to apply antibiotic cream over your whole body so why should we do the same thing to our farms?

Only it isn’t quite so simple. Do you remember I told you that the chemicals are often applied to the bare soil in autumn to try and prevent the weeds from coming up.  So how would a farmer know which areas of the field to spray if he can’t see the weeds he is targeting?

One solution is to map the location of the weed patches in the field in summer and then apply the herbicide in the following autumn based on the map produced the previous year.

However, this option is not being readily taken up by farmers. Why could this be? It seems like a sensible option right?

Well, it could be that the farmers don’t want to risk missing weeds that grow outside of these mapped areas. The patches could expand or new seeds could enter the field carried by animals or farm machinery.

So how can we reduce this risk? How do we capture all the possible parts of the field that might have weeds growing whilst still reducing the total amount of chemical we apply to the land?

Well, like all organisms, the places in which black-grass grows are influenced by the environment. There are certain environmental conditions that are favourable to its growth and some which are not.

You wouldn’t expect to see a cactus growing in the Arctic would you?

This is an extreme example but the same principles apply.

We can identify certain environmental conditions, in particular to do with the soil that are favourable, or not, for black-grass.

The question I am trying to answer with my work is this: Can we find a way to predict which areas of a field are more or less favourable for black-grass? Does it prefer heavy, wet soils or sandy dry ones for example?

If we can identify areas of a field that are vulnerable, then we could choose to only spray weed killer on those areas. This would reduce the amount of herbicide use overall, and minimise the risk of missing weeds that grow outside of the patches mapped in the previous summer.

So, to recap, farmers face many challenges every day. In order to try and control weeds on their farms they will often apply chemical weed killer across the whole field. These chemicals come at great expense to the farmer and the environment. By targeting where these chemical are applied we can reduce this cost whilst still controlling the weed problem.

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