A second dig at tillage

I posted a while back about the questions of tillage and fertility, and have since had an interesting debate about it with Patrick Whitefield, one of my favourite writers on matters agricultural and sustainable.

Patrick pointed out that I failed to mention in my post a major drawback of tillage – the oxidation of humus, the loss of which greatly diminishes soil fertility and contributes to climate change through the associated carbon dioxide. He also suggested that tillage gardeners probably import just as much fertility as no till gardeners, and that in any case gardens are high fertility places, so it’s legitimate to import fertility into them.

I think I have to concede all of those points, although I’m still not quite ready to give up entirely on my illicit affection for tillage. What I would say is that tillage is usually best avoided, so in any given situation if you face a till or no till option it’s always best to go for the no till, other things being equal. My point really was that other things rarely are equal, and gardeners sometimes get it into their heads that no till is just A Good Thing no matter what, like Velcro or Nelson Mandela, without putting it into a larger, whole systems context (I fondly recall the furtive whispers that broke out when some visiting permaculture design students set eyes on my rotavator). But if, for example, you compare somebody who grows a green manure ley and tills it in to somebody who buys in a truck full of cow manure, and you trace back all the environmental and energetic consequences of those two approaches, I don’t think it’s at all clear which option is best – in fact an analysis I did suggested that the tillage option would be better, but there are so many assumptions and difficulties with the data that I certainly wouldn’t want to stick my neck out on that one. Even so, I’m uncomfortable with the idea of importing bulky organic composts as an ongoing part of any putatively sustainable farming or gardening system, till or no till.

As Patrick points out, if you grow the fertility yourself on your site and figure out ways of getting it to your crops without tillage – as for example in John Jeavons’ methods – then that’s got to be the best system of all, and I’d agree. The problem really – which actually is a problem underlying a lot of the issues I discuss in these posts – is that such methods are quite labour intensive. They work well on garden scales, and less well on commercial scales. Large-scale commercial no till involves heavy herbicide and synthetic fertiliser applications – is that better than large-scale organic arable, involving heavy tillage? I don’t know.  Generally speaking, I think the more time spent by the more people growing stuff on the less area the better off we’re likely to be in all sorts of ways, but exactly where to draw the line is tricky.

There are other issues in the till/no till debate, some of which I mentioned in the previous post – for example leaching, soil biota, weeds and animal pests. One argument in favour of a green manure/ tillage regimen is that overwintering green manures prevent winter nutrient leaching. I’ve heard it said that really this is more of a problem with ‘conventional’ farming employing soluble nutrients, but I’m not entirely convinced – if you leave your well rotted compost out in the rain all winter I don’t think there’ll be much nitrogen left by the spring, but if anyone has any data on this I’d be interested. Physical weathering damage is also an issue.

On soil biota, tillage is pretty destructive (mostly of macrofauna), but not necessarily to the extent that it compromises the growing system so far as I understand the ecology. After all, a field or a garden bed is a heavily manipulated environment – and everyone agrees that there’s no such thing as a naturally balanced ecosystem anyway! On weeds, again I’m not sure – tillage can certainly put you on a weed treadmill, but then green manures can suppress weeds. Basically, there will be some kinds of weeds adapted to whatever regimen you choose to adopt, and it’s quite hard to judge which weed presentation is optimal – though I could probably be persuaded that no till approaches are generally better, at least on a small scale. On animal pests, here’s two photos of a little experiment we did this year – squash on the left transplanted into tilled grass/red clover and squash on the right transplanted into grass/red clover which was cut but not tilled at transplantation (the latter being the grassy bit with no discernible squash). The squash in the untilled bed were completely hammered by slugs (well, it was a bad year for it…) and possibly also suffered from competition and/or shading. Of course, this isn’t an argument against no till methods in general, though sadly it may be an argument against a specific method that otherwise might have combined the best of both worlds – a minimum till green manuring regimen with only occasional tillage.

Squash and tillage

Anyway, now that I’m not so tied up with commercial growing, I think I might try to run some little experiments comparing various different methods of till and no till growing. More on that soon. In the mean time, I think my message is: don’t till if you can help it – indeed, in the light of Patrick’s comments, even more so than I previously suggested – and if you do till, do it as infrequently and judiciously as possible. But always think about whole systems and not part systems when you devise your growing methods – if you do, it may turn out that an element of tillage could be the lesser evil.

But now I’ve cleared all that up, I’ve got to say that there’s really nothing quite as amazing as sitting in a tractor hooked to a plough with some nice sharp shares and watching the soil unzip behind you as it carves away off the mouldboards. Not the strongest argument for tillage, I admit, but…well, I did say I have an illicit affection for tillage!

2 thoughts on “A second dig at tillage

  1. Hi Chris
    I look at this in some detail on my blog.
    According to Jeavons it takes 1/2 inch of compost to maintain a high level of fertility, whereas Charles Dowding uses a 2 inch layer of compost for his no dig system. 4 times the amount.
    As for oxidation of humus, all that is happenning is that soil microbes are eating organic matter. As plants feed on the by products of microvores eating bacteria and fungi, the extra consumption of organic matter is just getting it closer to a form that plants can use. Providing that more is put in than is consumed, the net result is an increase in available plant food, and an increase in soil life.

  2. Pingback: pests and deficiencies | Urban Garden Apprentice

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