Agrosystems: how to harvest the most of an environment ?
To control and produce
An agrosystem is an ecosystem transformed by human in order to produce biomass for several potential uses (food, energy, construction ...). It is defined by the crossing between agricultural and natural surfaces, wild and dometicated animals and buildings, managed by humans.
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Livestock agrosystems are often presented as less efficient than crop agrosystems, especially in school textbooks. It can be true if the protein's origin is not specified : in livestock agrosystem, especially for dairy cows, the protein intake comes from non-human edible proteins, such as grass, hay, fodder. Chickens and pigs have diets similar to those of humans, and the benefits are less than for herbivores and ruminants.
In terms of energy production, crop production and especially cereals are undeniably more efficient than livestock production, but livestock production offers above all the interest of producing proteins with a high nutritional value, which can be important to a balanced diet as energy intake, as well as the capacity to valorize plant resources that cannot be consumed by humans.
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Sources :
[1] Peyraud, J. L. (2017, July). The role of grassland based production system for sustainable protein production. In 54. Annual meeting of the brazilian society of animal science (p. np). Brazilian Society of Animal Science. (european based study)
[2] van Zanten, H. H., Mollenhorst, H., Klootwijk, C. W., van Middelaar, C. E., & de Boer, I. J. (2016). Global food supply: land use efficiency of livestock systems. The International Journal of Life Cycle Assessment, 21(5), 747-758. (Netherland based study)
[3] Ertl, P., Klocker, H., Hörtenhuber, S., Knaus, W., & Zollitsch, W. (2015). The net contribution of dairy production to human food supply: the case of Austrian dairy farms. Agricultural systems, 137, 119-125. (Austria based study)
â– Monogastric workshops can be net producers of protein if the system use co-products of cereals and peas, rapeseed and sunflower cakes that cannot be consumed in human food.
â– Because of their short reproductive cycle and rapid growth, monogastrics need overall to consume less plant material per kg of meat produced than ruminants, which compensates for the fact that their diets rely more on food that can be consumed by humans. In addition, a higher proportion of their carcass enters the food chain.
â– The net efficiency of these workshops is highly variable depending on the composition of the feed. It would also be very strongly reduced in the hypothesis of an increased valorization of plant proteins in human food.
Monogastric animals (conventional pigs, standard broilers, laying hens) produce between 0.7 and 1.6 kg of animal protein per kg of human consumable plant protein, depending on the feeding method.
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â– French dairy cattle farms are often net producers of protein for human consumption, especially grassland systems[1],[2],[3]. To produce 1 kg of protein from dairy cattle (milk and meat), less than 1 kg of plant protein consumable by humans is used for a majority of farms.
â– Ruminant farms specialized in meat are rarely net contributors of protein. To be so, they must be very economical with concentrates and/or use mainly grass and/or plant co-products because ruminants are still poor processors of cereals.
â– The most grass-fed production systems will be less sensitive to an increased valorization of plant proteins in the human diet.
â– There remains a very large intra-type variability of systems which shows that significant margins for progress exist.
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Dairy farms produce from 0.6 to more than 2 kg of animal protein for 1 kg of plant protein consumable by humans. Their net efficiency is all the more important as the proportion of grass in the ration increases. The production of ruminant meat is less efficient, but above all, efficiency is very variable. While some transhumant systems do not consume any human consumable protein and thus have an "infinite" efficiency, some fattening workshops produce barely 0.2 kg of consumable animal protein per kg of consumable plant protein.
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Balance is the key
The objective of an agrosystem is to produce a resource that will then be exported to be sold: the system is therefore "withdrawn" of matter, carbon, nitrogen, etc., which must be compensated for by external contributions in order not to exhaust it (inputs, such as nitrogen fertilizers).
Ideally, one should therefore try to close the cycles in the agrosystem [1] (i.e. recycle matter to limit losses and waste), in order to limit inputs.
