Composting dilemmas

Maybe it’s time to write something about practical farm issues for a change, and what could be more practical than compost? In principle, compost is one of those ‘what’s not to like’ phenomena. You pile up unwanted organic matter that otherwise requires disposal, mix it with a bit of air and water and, hey presto, you end up with a magical substance that feeds your next crop and builds your soil. Compost is foundational to the organic farming idea of building beneficial biological cycles into farming practice.

But the practicalities of composting raise quite a number of dilemmas. Here are five:

  • on anything much more than a small garden scale, there is a considerable labour or energy cost to moving all that bulky organic matter to and from the compost heap – so much so that, before you know it, the energy advantage over buying in synthetic fertiliser is cancelled out, especially if you start trucking in manure from other people’s holdings
  •  if you don’t build your compost heap expertly – and to do so is a time consuming business – parts of it will go anaerobic and start emitting methane, which is a powerful greenhouse gas
  • likewise, if you toss in any old organic matter from the garden and don’t build a professional-grade hot heap your compost will be absolutely full of weed seeds which you will then distribute around your garden
  • unless you build a compost heap resembling Fort Knox, it will be a magnet for rats to build a cosy retreat from which they will sally forth all winter and make a terrible nuisance of themselves
  • if you use animal manure in your heap – particularly imported farmyard manure – the likelihood is that you’re basing your ‘organic’ farming on a synthetics-dependent and unsustainable livestock agriculture. You also risk importing all sorts of nasties into your soil, including various pathogens, antibiotic residues, aminopyralid herbicides that will kill your plants and – in my experience – quite often an assortment of terrible crap like old spark plugs and broken glass.

So, what is to be done? If I were running a small domestic garden, I think these problems would be manageable. And if I were running a large farm I’d use a big tractor and other energy-intensive kit to develop a decent composting system. It probably wouldn’t surmount the energy issue, but then nothing really does on a large farm. On the small farm, however, as with many things you get caught between two stools.

Steve Savage, a persistent critic of organic farming, decries its use of compost for similar reasons to those outlined above and advocates the use of anaerobic digestion instead. Such critics often forget that good old composted farmyard manure is widely used in conventional farming too, though perhaps only in those areas which have thankfully managed to retain a bit of mixed arable and pastoral land use and haven’t yet succumbed completely to the depressing uber-specialisation wrought by big agri where soluble synthetic fertiliser is king. Still, Savage has a point – in an ideal world, a digester is probably the best way to go. But then the argument tends to drift in favour of massive dairy farms or feedlots with ‘efficient’ industrial-scale digester facilities. I don’t know if there are any good energy lifecycle analyses of such facilities, or of large-scale mechanised farming machinery powered by methane, biodiesel or renewable electricity but if anyone could point to me to some, I’d be grateful. My feeling is that the whole-life energy costs, including building these big plants and then trucking the raw materials around, would be pretty high. Likewise with the opportunity cost of a fossil fuel-free industrial-mechanical agriculture would be high. But I’d like to see some good data. As I’ve suggested before, there are many other external costs of large-scale agriculture that suggest to me the wisdom of small-scale farming solutions, but I don’t deny that compost and fertility cycling is a problem for farming of all kinds which isn’t simply banished by scale.

One alternative for the small farm is a small-scale, backyard digester of the sort pioneered in China. My worry there is that if the facility isn’t very well built the chances are it’ll leak methane and lose its advantage, and to build it well may take more time and money than the average small farmer can really afford. But it’s a technology I’d like to keep my eye on. Some people coming from a vegan perspective are excited by such technologies as a means to turn grass into something useful without livestock. Call me old-fashioned, but personally I prefer to see ruminants on grass in mixed farming systems, though again it’s an intriguing idea and it would be worth seeing a good lifecycle energy or emissions analysis.

Anyway, the compromise strategy we’re currently pursuing at Vallis Veg is a much lower tech one. It has the following components:

Sheet compost

  • most of the fertility for the field crops comes from clover-rich leys, supplemented with a bit of manure from the livestock on the holding. The leys are tilled in as part of a tillage-minimising rotation
  • weed-free crop residues are added to the newest ley in the rotation as a kind of sheet mulch, with the aim of it breaking down slowly and aerobically over the 2-3 year life of the ley (see photo)
  • Cordelia uses our volunteers to build beautiful compost heaps which she polices terrifyingly in order to ensure that they’re weed free and nicely aerobic
  • nasty seedy-weedy stuff is either tossed callously into the field margins or put into a modified water butt to produce liquid compost
  •  the only stuff we routinely bring in from offsite is woodchips from local tree surgeons and a little reclaimed (not mined) peat. As I discussed previously the peat is used for our soil block transplants and I think is a tolerable compromise in sustainability, but in the longer term we’d like to minimise its use and make seed compost out of the wood chips, as Tolly does on his amazing site. We also plan to mix the urine from our compost toilets with the woodchips to make some handy, weed-free compost. Our rationale for the woodchip is that the tree surgeons are driving around with it anyway trying to find somewhere to dump it, so they may as well dump it on our site where we can make good use of it. It requires a bit of turning with a front loader or mini digger once in a while, but that doesn’t use too much diesel in my opinion. With its high carbon content it also takes a long time to compost down into something useful, but hey I ain’t going anywhere in a hurry.

It’s not perfect, but it’s the best I can currently think of. As always, I’d welcome any comments.

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