I have been mulling over George Monbiot’s recent announcement that he has become (almost) vegan in response to environmental impacts of animal agriculture. As a soil scientist concerned about maintaining soil quality and preventing soil degradation in the UK and overseas, I get a bit worried when people suggest we should exclude animals from our food production systems. We know that the best way to ensure healthy, productive arable soils is to rotate annual crops with longer term soil building grass/clover leys. Ideally, 25-30% of cropped land should be under a ley at any one time. It then makes sense to have some ruminants in the system to consume the forage produced by this soil-building phase. If we don’t do this, how can we incentivise farmers to leave land idle for so much time? And what about the need to maximize food production in response to growing world populations? Surely, well managed, mixed farming systems where animals are raised primarily on forages have a place in future sustainable food systems?
I started to read around the subject this week and came across this article by Peters et al. in the new journal Elementa, which investigates the carrying capacity of US agricultural land comparing ten different diets. They start their article by saying that one of the most perplexing questions in sustainability science is, “What should we eat?” (more or less how I ended my first blog!). It’s a fascinating study and well worth a read, but if you don’t have the time, some key points have been summarized in this short article. Their study focussed on the mainland US and included cropland (134 M ha or 31% of the total land available for food production) and permanent grazing land which is not suitable for cropping (299 M ha or 69% of the total). They assumed that at any one time about 70% of the total cropland was in cultivated crops (allowing about 30% to be in a soil-building grass ley as described above). The diets included a range of omnivorous options with different percentages of meat, ovolacto-vegetarian, lacto-vegetarian and vegan. While the vegan diet required less land to feed a person in a year, it also resulted in the lowest carrying capacity for the land because it essentially “wasted” the land that was in a soil-building ley and also didn’t use any of the permanent grassland.
It would be interesting to see a similar study conducted using the UK agricultural land base, but I suspect this would be further complicated by our reliance on imports, particularly of soya. The US has the luxury of a huge and diverse agricultural land base that can potentially feed their whole population – this made Peters et al’s study relatively simple. Our agricultural land base is only about 4% of what is available in the US, yet our population is almost a third of the US. So here we would have to consider scenarios with varying reliance on imports and consider the trade-offs among different dietary, environmental and ethical goals – lots of food for thought!