Friday, July 5, 2013

Agroforestry Systems Can Reduce Nitrate Leaching By 50%

Following on from Mike Barton's presentation to Beef + Lamb NZ, about farming under a nitrate cap. I thought I'd look at some less conventional ways farmers can reduce nitrate leaching.

Today I want to discuss Stephen Briggs Nuffield report into Agroforestry.

The report shows how an agroforestry system can dramatically reduce the amount of nitrate leached from a farming system.

It's a pretty radical change, but maybe the pasture based dairy farm of the future will include 100 trees/ha as well as cows.


Glen Herud here again and I'm blogging from my van today because I'm struggling to find time to blog. I still want to blog, but the only time I have to myself is when I'm stuck in Christchurch rush-hour traffic for 30 minutes every morning. 

So, I know I'm a bit weird.

I posted a video of Mike Barton last week about how he farms under a nitrogen cap. Heres the link to the full video on the Beef + Lamb NZ website. I recommend you watch it. 

But this is what he had to say:
"We leach 93% of the manageable nitrogen that's going into the lake. We wanted it to be all the batches and the septic tanks and the town and whatever else you could hope for. It wasn't. It was us."

You know, I think it's just a matter of time before all farmers will have to farm under a nitrogen cap. And whether that's right or wrong, I don't know. I just sense that the movement is towards that. 

When you look at the changes on the Horizons District Council, what's happened in Taupo. Canterbury is talking about it. Southland is talking about it. You know, I just get the sense in 10 to 15 years time, that's where we'll be.

And I don't think farmers are really thinking radical enough about how we could change our farming systems. I'm sure farmers understand how big the effect will be on their farming businesses. They understand that. But I think we need to really think about how we're going to farm under that, rather than spend all our energy on fighting it. Because I think it will happen, as Mike Barton said.

Now, one radical system, I'm going to cover a few radical ways that we could farm cows over the next couple of weeks. 


And I want to talk about agroforestry. The reason is that agroforestry has been shown to reduce nitrate leaching by up to 50% over a monoculture system. Now, Stephen Briggs is a Nuffield scholar from the U.K. and he released a report on agroforestry last year. And I'll put a link to it, it's really good.

But, what you do is you really combine trees with agriculture. So, they could be nut trees, fruit trees, timber trees and they could be cropping. Could be dairy, whatever. And what you do is you plant them in lines, you have about 100 trees per hectare. And you farm within the alleyways.

Now, the reason it reduces nitrate so much is that the tree roots will grow down deeper. And they go in underneath the alley crop and they join up in the middle. That creates a kind of a safety net. So, any nitrate that drops out the bottom of the agricultural system gets absorbed by those trees. Therefore, you have a much lower rate of nitrate leaching.

So, there's a lot of other advantages. For instance, shelter. Also, agroforestry systems have shown to have 30% reduction of evapotranspiration rates. So that means that you're losing less water out to the atmosphere. Which is probably pretty good for Canterbury farmers that particularly, when you think about our howling nor'westers in the summer. But it's not all plain sailing. Shading is an issue and Stephen talks about how to overcome shading and the research done on that.

I know Lincoln has done some research into agroforestry and they showed that, after 15 years, their pine trees have totally shaded out their alley crop. So, we don't want that to happen. There needs to be a bit more research done into it. But, you know, it's a radical way of doing things. I mean, imagine if your average dairy farm sort of looks like this and imagine just planting that full of trees. Planting thousands of trees in your most productive land. That's a pretty radical thing to do.

Now, these are the sort of things I think we need to start thinking about if we're going to have a dramatic effect on our rate of nitrate leaching. And of course, many people, many farmers, don't think we need to. 

But as Mike Barton says in his presentation, 'If farmers don't come up with the solutions, some bureaucrat in Wellington probably will.' And it's much better that farmers come up with solutions than someone else. 

So, I'm just going to throw out some real wacky, way-out sort of things that maybe we need to consider to reduce our environmental impact.


  1. I have been to the Lincoln site. Even contributed to the research.

    Pasture Production was halved.
    Wood production reduced by 8%

    This was under a sheep system. How do you stop cows ring barking your trees?

    How much nitrogen is sequestered by the trees? I am sure you know Nitrate is highly soluble and tends to follow the macropores in the soil. Is the tree growing fast enough to utilise much of this loss?

    Mr E

  2. Hi
    Maximum production is not necessarily the goal. Maximum value from the product is. If farmers have to farm under a nitrate cap then they should be able to get a higher value from the market for that.

    30 year studies overseas have shown production decrease of ag crop can be overcome.

    Many reasons why nitrate leaching is reduced under agroforestry. The trees absorbing water out of the soil in turn slows the rate of N leaching, this allows the N to stay in the ag crops root system longer. So it may not actually be the tree absorbing all the excess N. But it may well be too.


  3. good to see these creative ideas thanks Glen.

    i'd be interested in your thoughts on the trend towards biological farming - people seem to be able to get excellent production without urea by stimulating the bacteria & fungi in the soil.

  4. Thanks John

    Yeah I'm keen on learning more about Bio farming. I have a friend who converted his dairy farm to organic 5 years ago. He has some interesting results.

    I'll blog about it at some point.


  5. Hi Glen,
    liked the blog!
    With regards the previous comment about the Lincoln site: did they not have 200 stems per hectare? This density has since been shown to be too high in agroforestry systems. Newer more productive systems have greater tree spacings to reduce shading. The Lincoln site also found positive LER's I think? Please correct me if I'm wrong as I've found it hard to get access to the published results. A positive LER means it's more efficient to grow the trees and crops together than it is to grow them apart.

    1. Hi Alexa
      Thanks for the comment.
      Yeah I think they did find that 200 stems was too high, Stephen Briggs paper also says the same thing.
      A summary of the Lincoln findings are at the link below.

      I think the positive LER that you talk about is true and worth looking into further.


  6. Hi Glen,
    Great article. If you go low cost/ low input biological system(lower stocking rate) then Nitrogen leaching is almost a non issue. Did you read the article about Dr Sharon Woodward's three year mixed pasture trial at dairy NZ's Lye farm. Cows feed on mixed pasture excreted HALF the amount of Nitrogen in there urine compared to cows on standard Rye grass clover pasture. Cows on mixed pasture ate less but were more efficient and produced as much milk and sometimes more milk.

    1. Thanks for your comments Matt.

      I'll have to look up that research. Very interesting!

      Just read an article in the latest dairy exporter. Research by Lincoln shows that cows grazing fodder beet have much lower nitrogen concentrations.

      Good news!