Spring is in the air, the buds are bursting, the birds are at their nests, young lovers are canoodling in sunny parks, and – before I get too carried away – farmers are spraying s**t all over their fields. For indeed it is fertility in the latter sense that is my topic in the present post.

I’ve talked about woodland and grassland in recent posts, so I feel that I should now complete the set by talking about cropland. With cropland, fertility is a key issue, and I’ll come to it in a moment. But first I want to say something about the permaculture movement, which I mentioned in my last post. Permaculture has been increasingly influential on many home gardeners and urban environmental activists. It was certainly what first influenced me to start thinking about food production and environmental issues. But it’s had less influence on commercial, broadscale growing, the game I’m currently playing. I suspect that many permaculturists might argue that this is because broadscale growing is behind the game. Permaculture emphasises no till growing, perennial crops and maximum crop diversity, whereas commercial growing – and commercial farming even more so – remains stuck on the treadmill of tillage, annual crops and monoculture.

That may be a fair criticism, but I believe there are grounds for commercial growers not only to justify doing what they do, but to return fire to the permaculturists, for cherished ideas such as no till and perennial polyculture can easily become ill-considered dogma. I have no wish to set up an argument just for the sake of it. What I hope to have suggested by the end of this post is that there’s merit in both viewpoints, and together they may help us chart a more considered path towards achieving a long-term sustainable agriculture.

So, coming back to fertility, the first point to make is that our crop plants are hungry things and cropland is hugely more fertilised than is generally the case among wild ecosystems. In stable wild ecosystems, most plants are adapted to cope with low nutrient inputs, or else with irregular pulses of nutrient input  (such as when a passing animal urinates in the vicinity) – often being helped in the latter case through association with mycorrhizal fungi (source: J. Philip Grime, Plant Strategies, Vegetation Processes and Ecosystem Properties). In fact, something like half of all the world’s soluble nitrogen results from human agency (source: Vaclav Smil, Enriching the Earth), which is pretty bad news because this uses a lot of non-renewable energy and causes water pollution, greenhouse gas emissions and biodiversity loss.

All that is true of organic as well as synthetic fertiliser, although the problems may be less in the organic case. It’s probably easier for conventional farmers to give their crops the correct amount of fertiliser exactly when it’s needed, but on the other hand synthetic fertiliser probably has higher energy costs and is more soluble, and hence potentially more polluting.

I say synthetic fertiliser ‘probably’ has higher energy costs, because in the organic case a lot depends on where the fertility comes from. Suppose that you buy in a load of municipal green waste compost, or cow manure from a conventional farmer, or horse manure from a local stables. You need to factor in the source of the fertility and the costs of getting it to your site: organic manures are bulky, with low nutrient densities, so once you start trucking them around the energy costs quickly mount up. If they’re  from conventional farms then they’re likely to derive ultimately from energy-intensive industrial synthesis, and the same is true if they’re from a stables – or at the very least they’ll derive from a rather questionable land use. I’ll provide some specific figures to back up these claims in a future post (you can also find some on the Research page). It might be argued that the green waste or the animal manures are waste products that might as well be used by organic farmers, but I’m not convinced. If those fertilisers were reused at source it would save drawing down more non-renewable resources in fertiliser manufacture for the next input cycle, and save on transport costs as well. Organic growers buying in fertility in this way are feeding off the bloated body of the fossil fuel economy – it’s a bit like driving to the bottle bank with a few empties in order to ‘save’ energy.

So what are the alternatives? Well, there are a few, but the only one I find really convincing as a general strategy is to grow legume-rich cover crops (‘green manures’), particularly clover – an approach covered in depth in Jenny Hall (now Jenny Griggs) and Iain Tolhurst’s brilliant book Growing Green. The main problem with this from a permaculture perspective is that you can’t easily establish crops into a clover sward; the clover needs to be tilled in first, and according to permaculturists tillage is to be avoided. There are five main reasons why:

• it uses (fossil) energy
• it can lead to soil erosion
• it can damage soil structure
• it kills soil biota, including mycorrhizae
• it brings up weed seeds

For these reasons, a lot of domestic-scale gardeners decide to adopt ‘no dig’ methods and import the fertility from offsite, which isn’t difficult on a garden scale. This isn’t really an option for larger-scale growers, because you can never find and transport enough manure and compost, and this draws you into leguminous leys and tillage. But of course if you perform an energy audit, a thousand home gardeners each importing a ton of compost is not energetically better than one farmer importing a thousand tons of it (in fact, it’s almost certainly worse). Furthermore, I think the objections to tillage should probably be rewritten as follows:

•  it does use energy, but not as much as trucking in manure, especially manure deriving ultimately from synthetic fertiliser.
• it can lead to soil erosion, but in moist temperate climates with heavy soils such as here in western Britain it doesn’t have to – as is evident from the fact that people have been tilling soils here for many centuries. The same isn’t true of arid places, like much of Australia where permaculture was first formulated and where tillage is much more problematic.
• it can damage soil structure, but if you’re careful when and how you till much of the damage can be avoided
• it does kill soil biota, especially mycorrhizae and larger fauna such as earthworms, but if you’re dumping a huge amount of nitrogen and phosphate onto the soil then mycorrhizal action is of limited relevance anyway, the more so because important crop groups such as brassicas and chenopods aren’t mycorrhizal. Tillage replicates early-succession bacterially dominated soils which are what vegetable crops require, so although in an ideal world the destruction of soil biota is best avoided it’s not necessarily that problematic for crop growth.
• it does bring up weed seeds in my experience, although different methods of tillage do it to different degrees and some authorities even argue that some types of tillage can reduce the soil weed seed bank (source: Davies et al Weed Management For Organic Farmers). Ultimately weeding is a price that growers have to pay for interfering in the ecological succession – and no till growers have to do it too by weeding out incoming seed drop, or dealing with the consequences of weedy manures.

All things considered, I think it’s preferable to grow green manures and till them in rather than adopting no till systems based on imported fertility. I think the permaculture movement and other alternative farming advocates have erred in putting too much emphasis on tillage and too little on input provenance. I don’t doubt that the ‘organic’ gardener who slaps down huge amounts of imported compost can achieve impressive vegetable yields…but then again so can the conventional grower. We need a whole system approach that focuses on achievable sustainable yields.

But green manure systems are still quite crude, amping up the nutrients and potentially resulting in the same problems of over-nitrification that I mentioned earlier. And when all is said and done, it’s best to avoid tillage whenever possible. How wonderful it would be if we could replicate wild ecosystems, with our crop plants adapted to low nutrient input and nutrient pulsing through mycorrhizal associations. That would be true permaculture farming. But let us not run before we can walk. I don’t see the logic of adopting a no till approach on the grounds that it’s more ‘natural’ and then unnaturally importing truckloads of factory-derived compost. Why not first of all focus our efforts on better nutrient cycling, and on optimising organic crop rotations so as to keep tillage to a minimum?