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Doing the sums - does organic farming stack up? | |
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What is organic farming? Phosphorus use in historical farming |
Anthony Trewavas, professor of plant biochemistry at the University of Edinburgh, is one of the sternest critics of the organic farming lobby. Making use of every opportunity that he can, Trewavas has tried to counter the easy assumptions made about organic farming, and which he believes do not stand up to scrutiny. One of his concerns is that organic farmland becomes progressively depleted in soil minerals because there is a failure to replace the minerals lost in the form of crops and livestock. This is a criticism that has been around for a few years now, but with no one in the organic world stepping forward to rebut it with any facts, or to explain how it is that organic systems are actually sustainable. Thus is organic farming flawed or is Trewavas missing the point? What is organic farming? Organic farming gives primacy to livestock in an idealised mixed farming system, the inclusion of animals being obligatory in the minds of organic advocates. This system is based on the Norfolk rotation, devised in the eighteenth century and which alternates the grazing of farm animals with the production of arable crops. A proportion of the latter is grown for livestock feed and thus not all of the arable phase in the rotation is for human consumption. Organic farmers also apply animal manures when these are collected away from field situations, and they apply liming agents provided they are only crushed forms of parent material. The use of chemical fertilisers to replace soil minerals is eschewed. They seed their fields with clovers as well as grass when they are put down to the grazing ley of the rotation, and then plough this in to be ready for the first arable crop of the rotation. Let us examine the role of the livestock in organic farming systems, and trace this rotation through to try to understand what is happening to soil minerals. Herbivores (cattle and sheep) turn grass into animal protein while functioning as mobile compost makers as they distribute their wastes over the fields. There are undoubted improvements in topsoil condition from this involvement of livestock. Firstly, the grass cover of the ley will always improve soil through root penetration of topsoil, manuring from grass litter debris, and from protection of the soil surface from the elements. Secondly, livestock return some of that grass fraction as animal manure that will also improve the topsoil through the wastes being turned into humus by the soil. Thus there maybe some build up of fixed carbon in the soil (originating from photosynthesis in the grass) but there would be no net increase in minerals unless there were the nitrogen fixers in the grass ley, such as clovers, or if additional manures were brought in from elsewhere. Thus it is the clover, and not livestock, that make a difference to soil mineral content by bringing about an increase in soil nitrate. In the absence of imported manure sources, the livestock are just recycling existing topsoil mineral content via the medium of the consumed grass. As livestock grazing is an extractive process - from a calf growing into cow and then on to fattening - there will actually be a net loss of minerals, particularly in the calcium and phosphorus of bones when the livestock are removed and culled for eating. Even the increase in topsoil organic matter (see above) is likely to be a short-term gain as it will be lost through oxidation when the land is ploughed up for the cereals that follow livestock in the Norfolk rotation. You can get the increase in soil nitrate without the involvement of livestock by just ploughing in the grass and clover after an ungrazed ley period. While you would miss out on the mobile compost element of livestock, you would have the advantages of the grass growing in the soil (as given above) and there would not have been the extraction of minerals needed to support the growth of the livestock. This was the point made by the Vegan Organic Society (VON) in their call for animal free cultivation (press release, May 2001). In their analysis, VON recognised that soil mineral replacement in organic farmland was dependent on the import of animal manure over and above that produced and recycled by grazing animals. Most people like to think of organic produce as having been grown by the use of manure that comes from organically reared animals. However, as VON pointed out, there is not enough organic manure from certified farms to support commercial UK organic vegetable and cereal production. They concluded that what is actually going on in commercial organic horticulture, is that fertility in these systems is coming primarily from manure from conventional chemical based agriculture. Thus the soil mineral replacement in farmland under organic horticulture was arising from chemical fertilizers spread on mainstream farmland. Those fertilizers would be turned into grass or other plant material, which is subsequently turned into manure by conventional livestock and is then transferred onto organic farmland. VON proposed a new relationship with the soil, where organic food can be grown without the use of animals. They pointed to a number of research programs on stockless organic horticulture, such as at Elm Farm Research Centre. This is an organic test farm in Berkshire that set up a stockless system of arable farming some ten years ago. It was based on three different rotations for cereals and roots and which replaced the livestock phase of the rotation with a soil cover of leguminous (nitrogen fixing) green manures. This was an important initiative because most mainstream arable farmers would be not be interested in bringing in livestock just to become converted to organic orthodoxy - the sheer burdensome cost of the stock and the amount of fencing needed to contain them is the disincentive. The question that was posed by this stockless system was whether the removal of livestock would result eventually in a reduction in arable yield, as orthodox organic wisdom would have said. However, eight years of stockless rotation gave no fall in yield. There were problems with weeds and with soil compaction, but this was related to the absence of grass in the phase with green manures in the rotations. The grass could have been put into that phase irrespective of whether it was to be grazed by livestock, and this has now been adopted in a planned rotation for field scale stockless organic vegetable production. So with an extractive process of arable production, and with no livestock involved, why didn't the topsoil nutrient exhaust when there was no obvious replacement of the soil minerals? Elm Farm missed an opportunity to examine this as, although they measured the off-take of minerals each year in the rotations, they did not relate it to soil mineral capacity, but only to any observable change in yield. Unfortunately, the study has come to an end because of the inability to get the same seed varieties to continue and maintain coherency, but there maybe an explanation to which I will return to later. Other stockless research systems have substituted the imported animal manures of organic orthodoxy with compost produced from green waste collected from urban households. Thus soil mineral replacement is possible by this method without the involvement of livestock, but it suffers from the same analysis as with the imported animal manures. It is likely that most of that green waste arose in circumstances where chemical fertilisers were applied to the soil. Thus it could be argued that it is disingenuous of organic farming to say that they eschew the use of chemical fertilisers, albeit being mediated by an incorporation of the minerals from those chemical fertilisers into plant material first, and that material composted either by livestock for the animal manures or by ourselves for green waste compost. Phosphorus use in historical farming -top I would go further and say that at its current rate of internal analysis, the approach of organic farming can only but lead into a dead end. An article in the periodical Organic Gardening cast light on soil mineral turnover in farming systems. Based on a paper in the Journal of Applied Ecology (Phosphorus balance of contrasting farming systems, past and present. Can food production be sustainable? 1997, vol. 43, ppg 1334-1347) Ken Thompson recounted the work of E.I. Newman in analysing the historical knowledge of farming and its use of phosphorus in soils. Detailed records for a farm of the 14th century on farming activity and on crop yields allowed Newman to work out a balance for soil phosphorus that was shown to reduce in coincidence with declining cereal yields. Clearly the farm would have been managed in way that would be recognised by organic enthusiasts today, but it was also clearly unsustainable in the long term. Other studies of earlier farming systems in the paper confirmed this, which raises the question that if supposedly organic methods then were unsustainable, why should they be sustainable now? Thompson nails the irrelevance of animal manures, pointing out the obvious that grazing is just a recycling of topsoil mineral. Also, the import of animal manure is taking soil mineral from one place and putting it on another - a horizontal redistribution that doesn't increase the total amount of phosphorus in soils. What does do this, and has been the change over the last few centuries, is that hundreds of millions of tons of rock phosphate have been mined from around the world and have ended up as fertiliser spread on to fields. Thus the developed world has become awash with phosphorus and organic farming is living off the back of that fertiliser application (this could be the reason why Elm Farm saw no drop in yield in their stockless system). Turn our farmland completely organic tomorrow and eventually the phosphorus will run out, ending up, as with most other soil minerals, in the human wastes that are dumped in the sea rather than recycled on to the land. Style over substance - the claims of organic farming -top Soil management is regarded by organic farmers as the strength of their farming system and thus it is perhaps ironic that it is becoming one of the major areas of criticism of organic farming, with people waking up to the fact that there is no critical analysis of the system that stands up. It is not just the problem with depletion of soil minerals. It is also the heavy reliance on ploughing as part of the rotation and in the management method for the greater weed problems that organic farming suffers. Elsewhere, the trend in agriculture is towards minimum tillage systems to reduce soil carbon loss and to lessen the destructive effects of ploughing. Thus organic farming is flawed and there is a reason for this that Trewavas has shrewdly identified: organic farming is less a coherent set of instructions for growing things than an ideology, part of an overall philosophy of life that emphasises the place that mankind occupies in nature. Knowing our place in nature is perhaps an imperative for us all, but organic farming is a philosophy that is aspirational about its effects on nature rather than being analytical or definitional about what its consequences are and how it achieves its aims. What it proclaims is arbitrary. It wishes nice things to come true, but without consciously or rationally doing anything to make it so. In addition, as befits an ideology, there are many jarring contradictions between the claims of the organic lobby and the reality. This was picked up in a letter that was also in Organic Gardening magazine (Jan 2002). Dave from Darlington is an organic enthusiast, but he stood up for the Advertising Standards Authority in his letter, even though it had ruled that organic farming should not be described as sustainable. He listed organic farming's faults: a heavy reliance on fossil fuels to power tractors; the deleterious effects of ploughing on soil structure and composition: the food miles associated with so much certified organic food (greater that 70% has always had to be imported); the unnecessary reliance on livestock; and the lack of a coherency that should look to the welfare of people as well as livestock. Dave's judgement was that it did the organic movement no good to make unjustified claims about its achievements so far. A new paradigm for agriculture -top Dave is a member of VON. He thus represents one of the few who have made the break from the straightjacket of organic orthodoxy by becoming more thoughtful in his approach to food production (his vegan adherence in no way invalidates his concerns). Sadly, debate around the future of food production ends up with the either-or polarities of organic farming versus the spectre of an industrialised production process, not allowing that there are other realities. To open your eyes to one, here is a paradigm from history that provides another route for soil mineralization. Trees were re-introduced into the Scottish landscape in the seventeenth century, as it was known that their leaf litter would manure the ground and reverse the trend in falling crop yields. Other improvements, such as liming, the Norfolk crop rotation and the concerted use of animal manures came later. What is the secret of trees? They link the topsoil with the subsoil beneath, such that minerals are mined by tree roots from the greater supply below and are deposited on the soil surface. Many cultures are aware of this and take advantage of the property. It is one of the reasons for research programs in the development of agroforestry, systems that combine the growing of trees with crops such as grass or arable. And it is one of the key fundamental approaches in Permaculture Design, an applied earth science that sets out rationally to integrate our activities with nature. Mark Fisher, 25 January 2002 www.self-willed-land.org.uk mark.fisher@self-willed-land.org.uk |