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Green manures: digging up answers

Green manures: digging up answers

We've been figuring out what makes a good green manure.

What better way to spend a cloudy mid-January day, than digging up worms?  I was out on a farm in Lanarkshire last week doing just this, as part of a green manures field lab (an on-farm research trial).

What are ‘green manures’? 

Green manures are crops that aren’t grazed, or harvested and sold.  They are simply left, or put back into the soil, before the next crop is sown.

Why would you do this?  Surely farming is about growing and selling produce? 

Yes, and it is also about looking after the soil in the longer term, and helping the environment.  Green manures should help do both of these things. 

So how can we tell they are actually helping?

Lots of farmers in Scotland want to know the answer to this question, so Soil Association Scotland is running a field lab to try and answer it, which is why I was out in the field last week with my spade.  A farmer is growing four different types of green manures: with different seed mixes, and ways of sowing these mixes.  We are doing some assessments in the field to see their effect on the soil, and the benefit they’ll have on the crop sown next.

What does this have to do with worms?

Worms are a really simple and effective way of measuring soil health – if the soil is happy, then so are the worms.  I’m interested in how many worms there were, how much they weigh, and how many different types of species there are.  This gives us an idea of the amount of other soil biology there is, and the ‘health’ of the soil.  I was also interested in the structure of the soil (some green manures were better than others for this), and the qualities of the different green manure crops themselves (how big their yield is, and their protein and mineral content). 

So are green manures worth growing?  Which one is best?

We can’t answer that question yet!  Our measurements are starting to give us a picture of the benefits, and the differences between the different types of green manures.  We’ll need to do quite a few more, including soil analysis, and having a good look at the following crop before we can draw any conclusions. 
In the meantime, why not come out and see the green manure crop yourself?  We will be holding a meeting in Thankerton on Thursday 2nd March.

Fancy having a go?

If anyone else wants to find out the benefits of green manures, why not run a trial yourself?  If you are sowing a green manure for greening compliance, as part of an AECS scheme, or just because you want to try it out, then why not try out a few different mixes, and tell us about it? 

If you want to have a go at this then contact me, David Michie, on 0131 666 2474 or at dmichie@soilassociation.org.