Closed loop fertility possible or doubtful?

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Closed loop fertility possible or doubtful?

I had a chat with one of my allotment neighbours two days ago, a guy who with his partner has a very pretty allotment, packed with really good looking veg, lots of it and in wooden sided raised beds. He seems quite a progressive kind of guy so I started talking about sustainability and how his quinoa stalks and corn stalks, when composted, would add fertility to his plot. Of course, he replied, both those plants don’t add anything to the soil.

And he may be right.

Because I am an argumentative, political, kind of bloke I rely on my gob to keep flapping to win arguments. But I was a bit stumped.  I came up with some guff about all organic matter feeding microbes that multiply, die off and add more plant food than you had before, but the way I trailed off suggested even I didn’t believe it, and I was the one talking. Plus his family farm acres in America and they have compost heaps the size of my allotment plot. They know that external inputs create fertility (manure and fertiliser) and the proof was in front of me, in front of my own eyes, in this guy’s allotment.

Have I been sold a pup?  I need to audit what I’m doing.

I don’t necessarily believe (from the doubt that has crept in) that recycled organic matter does the business. Therefore, my 100 sq feet of broad beans (fava) will not add any further fertility to the soil than was already there. The plant is nitrogen fixing but all of that nitrogen, apparently, goes into making the beans and not into the compost heap. John Jeavons says that it is the carbon we are after to fill up our compost heap, thus allowing us to enjoy our beans, but I think it is the nitrogen, because the plant uses clever biology to add it from the air – a new resource that wasn’t in the soil in the first place. This means, if I am right, that I have to cut down the broad beans before they make beans. I can’t have my cake (fertiliser) and eat it (food).

So what am I doing, on the plot, that I know actually raises and maintains the fertility in the soil?

1) I have two young hedges of nitrogen fixing trees that I will trim to provide nitrogen for the compost heap and, because they are trees, draw up nutrients from deep in the soil. There are other benefits, hedges control soil erosion, provide habitats for wildlife and provide hiding places for cats to ambush pigeons when they try to scoff my brassicas.

2) Interplanting my crops with nitrogen fixing clovers and vetches during the growing season

3) Growing nitrogen fixing green manures (again clovers and vetches) during the autumn and winter on my growing beds.

4) Several large clumps of comfrey. Yes, I know it doesn’t add anything to the soil that wasn’t already there, but myself and others have had good results from it, and it doesn’t seem to run out of nutrients.

5) Growing perennial nitrogen fixing clumps of sweet peas (the everlasting kind) and composting the greenery in the autumn.

Not too bad, though I don’t think I am going to be able to stop using inputs next year, I should be able to halve them. That being said, the compost heaps are starting to look good and big, and may provide a substantial part of the 48 buckets of compost I need according to the biointensive system. Sadly, though, I’m not sure I believe in the value of my own compost anymore. Anyway only one way to find out and that is by experimenting, growing veg and eating it. If I get any at all that is.

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