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Agricultural recycling, an ancient and contemporary practice

Under construction

Epandage sur EFELE
© Morvan
Spreading organic materials, old and contemporary practice raising questions

Spread in agriculture, knowing and controlling the effects in the field

The application of manure and other livestock manure is a common practice to recycle nutrients and organic matter with dual interest: (i) agronomic for the maintenance of soil fertility, and, (ii) environmental, for the potential storage of organic carbon that can contribute to the mitigation of climate change (Plan 4 pour 1000; http://4p1000.org/comprendre).

Sources of organic waste products (OWP) valued in agriculture are currently diversifying, with urban, industrial / agro-industrial and agricultural origins. These spreads ensure the recycling of the main elements contained in OWP (eg C, N, P, K), (i) by replacing non-renewable resources (example of P) or whose synthesis consumes a lot of fossil fuels (nitrogen fertilizer) and (ii) contributing to the development of a circular economy within the territories. Furthermore, the development of the treatment of these organic resources, through methanation in farms, increases farmers' autonomy according to their energy needs (EMAA plan, Energy Methanation Nitrogen Autonomy).

However, these residual materials may be vectors of biological or chemical contaminants and it is important to ensure the safety of their use in agriculture. On the other hand, an uncontrolled use of OWP can lead to losses of nutrients that contaminate for example water (nitrates, phosphates). Therefore, their use in crop cycles must be optimized.

OWP valorization in agriculture should contribute to the development of agroecology subject to the sustainability of production systems including these recycling practices.

Yet, this agricultural recycling requires to apprehend in the short, medium and long terms the agronomic values ​​of OWP spread in a variety of agro-pedo-climatic situations, and to estimate all the potential impacts and the possible risks associated ( over-fertilization NP, losses by runoff, leaching or gas emissions, possible input of contaminants which increase their (bio) availability). This is possible particularly via long-term field experiments carried out according to agricultural practices, approaching real practices and allowing the monitoring of agro-systems subjected to repeated OWP spreading.

Epandages_Rennes

Figure: Cattle manure spreading on EFELE site (Morvan et al.)

Context of the Esco MAFOR request made in 2014, Translated Extract Esco MAFOR

“While the return of animal manure to the ground is a multi-century agricultural practice, this organic fertilization method has evolved according to the evolution of systems and livestock management. During the 20th century, it was mostly supplemented or supplanted depending on production systems and regions, by the use of mineral fertilizers for a controlled intake of the three basic nutrients nitrogen (N) , phosphorus (P) and potassium (K). More recently, fertilizers of residual origin have been added from various other effluent and waste treatment processes (urban wastewater, household waste, industrial effluents, etc.). In a context where the desire to reduce the amount of waste generated and to recycle them is combined, the rise in the cost of energy required for the production of synthetic nitrogen fertilizers, the depletion of mineral resources, particularly phosphorus, and the degradation of organic matter levels of soils reinforce the interest to reuse in agriculture the organic part of our waste.

Ademe has estimated that 355 million tonnes of waste were generated by human activities (domestic and industrial) in France in 2009. Agriculture and forestry, for their part, are responsible for the production of 374 million tonnes of livestock manure (manures, slurry) and crop residues, most often valued on site. These quantities, stable over the last decade, place France in the average of European countries in terms of the amount of waste generated per person per year. The "deposit" of fertilizing residual materials (FRM or Mafor in French), appears therefore consistent and able to substitute at least in part for mineral fertilizers.

The use of these materials with diverse origin, and therefore diverse natures, is questionable. First of all, associating differently the three basic elements N, P and K, they are less flexible to use than the mineral fertilizers of which the farmer knows a priori the precise composition in fertilizing elements. The spreading of such materials may also be reluctant or even rejected by their potential users, especially when they are not direct producers, and / or by the nearby living populations. The greatest worry  are the environmental impacts that the use of these FRM can generate. These are of several types. The spread of FRM can lead to leakage of nitrogen into the environment, which is a source of pollution, a phenomenon partly studied in the context of the ESCo "Farming and Nitrogen" for livestock farming effluents in regions with a high concentration of animal production (INRA, 2012). Given the residual nature of the FRM, they are also likely to provide a set of contaminants in soils (pathogens, organic and mineral) that can accumulate and be transferred to the plants and animals that ingest them. As most of these contaminants may represent a danger to human health, public authorities must remain vigilant on the risks of their transfer to humans due to agricultural or forestry FRM uses. From this point of view, three major sectors with different stakes can be distinguished. While all FRM are likely to bring chemical contaminants to the soil, materials from agricultural operations, mainly livestock effluents, and materials from urban wastewater treatment contain fecal matter. They are therefore likely to bring to the soil pathogenic microorganisms. This type of input does not apply to industrial or household waste. "

EscoMafor_Couverture_2014

Figure : ESCO MAFOR 2014