To grow a crop of apples, an apple tree needs a balance of light, water, temperature and carbon dioxide. It also needs nutrients, like nitrogen and phosphorus and potassium. In nature, one of these things is always going to be in limited supply, controlling a plant's growth. Adding more water won't do a thing if the tree is short on phosphorus; more carbon dioxide is no use if it's too hot. The science of crop productivity is, in a way, the science of managing limiting resources.
Modern farming techniques, such as chemical fertilizers, irrigation and greenhouses, are meant to try to control the supply of these resources. Organic farmers, who do not use chemical fertilizers, still try to manage their crops' resources, often by spreading manure or organic fertilizers. But crop yields from organic farming tend to be lower than those from conventional agriculture. And without a steady stream of nutrients flowing from conventional farms to organic ones, says a new study by a team of French researchers led by Benjamin Nowak, organic crop yields would likely be even lower still.
In their study, Nowak and his colleagues tracked the flow of nutrients through organic farms. They found that the bulk of the nutrients used in French organic farms still ultimately came by way of conventional agriculture:
Nutrients entered the organic farms mainly through fertilizing materials (manures and fertilizers) and, to a lesser extent, through feedstuffs, fodders and straws. More than 80% of nutrient inﬂows through manures (82%, 85% and 81% for [nitrogen], [phosphorous] and [potassium], respectively) and more than 95% of [nitrogen] and [phosphorous] inﬂows through fertilizers came from conventional farming, whereas 61% of [potassium] inﬂows through fertilizers came from mineral sources. Approximately half of the fodders and straws came from conventional farming, whereas all of the feedstuffs came from organic farming.
The nutrients in the manure and organic fertilizers, the scientists say, do not exclusively come from chemical fertilizers, though much of it does. In general, roughly a quarter of the nitrogen, three-quarters of the phosphorous, and half of the potassium on the organic farms had originated at a conventional farm.
Our results suggest that organic farming strongly relies on conventional farming, especially for [phosphorus] and in the case of stockless farming. This should be of interest for future scenarios on global food production.
Organic agriculture food production rates are currently around 75 percent to 80 precent of those of conventional agriculture, but the authors suggest that, if organic agriculture takes off in place of conventional agriculture, these production rates could drop further.
“[A]ccounting for nutrient ﬂows from conventional to organic farming and, therefore, indirect reliance of organic farming on manufactured fertilizer,” the authors write, may undermine the idea of a fully organic agricultural system.
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