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Misconception Number 31: There are not enough cows in the world to provide enough nutrients in terms of cow manure for today’s food crops.
Summary of Counter-Arguments:
- Cow manure is not the only source of nutrients for organic farming; other sources of nutrients include, but are not limited to, green manure (leguminous plants), compost, mulch, and seaweed.
- Green manure actually has the potential to provide much more than the quantity of nitrogen provided currently by synthetic fertilizers worldwide.
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Details of Counter-Arguments:
Cattle and other farm animals are not the only sources of nutrients for organic farmers to maintain soil fertility. First of all, cows and other animals do not themselves produce nutrients. They basically concentrate nutrients in a form that is easier to spread in the field (e.g., they collect nutrients from pasture lands through grazing, which they then process, assimilate, and concentrate the undigested parts in feces, defecate in the barn at night where the farmers can easily collect the manure to be spread on their crop fields. Hence, these animals allow nutrient transfer within the farm, which facilitates maintenance of nutrient/mineral soil fertility. In addition, the animals provide organic matter that increases biological fertility of the soil and stabilizes its physical structure (something that synthetic fertilizers used in conventional agriculture cannot achieve). There are several other methods that are used by organic farmers to recycle and redistribute nutrients within the farm, as well as to increase the organic matter content of their soils. Applying compost and mulch with crop and other vegetal residues from the farm also commonly contribute to soil fertility and structure on organic farms. Furthermore, in developing countries, small organic farmers use a range of creative practices, such as collecting alga from farm ponds to spread on crop fields.
In addition to the nutrient sources available on-farm, organic farmers can use several methods to bring in nutrients into the farming system, which helps compensate for soil nutrient losses caused by harvest.
- Green manure refers to the use of leguminous crops such as clover, alfalfa, beans, peas, groundnuts, and other such plants to increase nitrogen content of the soil. These plants, through a symbiotic association with bacteria, capture the nitrogen in the air and fix it in their own cells, but also directly release some of it in the soil. It is now widely recognized that planting green manure plants between growing seasons provides enough nitrogen to the soil, organically, without synthetic fertilizers. In fact, scientists have recently demonstrated that some agrichemicals significantly disrupt symbiotic nitrogen fixation [1]. Therefore, green manure plants have even more potential under organic management.
- Mineral fertilizers are natural fertilizers such as natural phosphates, mineral potassium, and calcareous and magnesium amendments that are allowed in Organic Agriculture.
- There are other fertilizing inputs that organic farmers can use (e.g., guano, seaweed, biodegradable byproducts of food, feed, oilseed, or textile processing, wood and forestry products, and peat).
The needs and uses of nitrogen vary depending on the region of the world, but overall, much more nitrogen comes from green manure than from animal manure [2]. Analyzing 77 studies conducted in temperate and tropical countries, scientists from the University of Michigan concluded that an increased use of leguminous plants could provide 58 million tons more nitrogen than the current quantity of synthetic nitrogen used every year for agricultural production. Research at the Rodale Institute in Pennsylvania showed that red clover used as a winter cover in an oat/wheat–corn–soy rotation, with no additional fertilizer inputs, achieved yields comparable to those in conventional control fields. Even in arid and semi-arid tropical regions such as East Africa, where water availability is limited between periods of crop production, drought-resistant green manure plants, such as pigeon peas or groundnuts, could be used to fix nitrogen.
[1] Proceedings of the National Academy of Sciences (June 12, 2007, vol, 104, no. 24, 10282-10287).
[2] Can Organic Farming Feed Us All? World Watch, Volume 19, Number 3, May/June 2006.
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