(120f) Integrated Framework for the Design of Intensive Cattle and Agricultural Operations Towards Circular Economy.

Nowadays, the specialization of agriculture and the intensification of livestock have separated both sectors, so that dairy and meat production are located in one place, and crops are grown in another. This leads to a dependence on mineral fertilizers in crop areas and an excess concentration of nutrients in livestock areas (Rick Kersbergen,2021). On the one hand, livestock is one of the main generators of anthropogenic CO₂ (IPCC,2014), in addition to other environmental impacts such as contamination of soils, eutrophication of water resources, and the generation of bad odors (FAO,2006). On the other hand, the increase in the population worldwide has pushed agricultural systems to increase their production and cultivation area increasing the total consumption of mineral fertilizers. Its excessive and uncontrolled use does not only imply an increase in the carbon footprint due to the energy used to obtain the mineral fertilizer, but also contamination of soils and water resources due to the excess of nutrients (Lammel, 2001). Organic waste can be treated through a system that integrates anaerobic digestion (Kafle,2016), struvite production (Martín-Hernández,2020), and ammonia stripping (Lei,2007) to produce biogas and organic fertilizers, which can be used to reduce the use of mineral fertilizers in crops.

Integrated farming and livestock systems simulate natural energy and nutrient cycles by converting cellulosic ruminant feed into protein and recycling nutrients from livestock manure into the cell structure of crops (Oltjen and Beckett, 1996). Nowadays, these integrated systems refer to small organic farms (extensive livestock) where such integration consists of a grazing activity where manure is deposited naturally (Reddy,2016). To extend this integration to intensive systems of thousands of animals, it is necessary to control and understand how the nutrients are transformed in the digestion process of the animals. The target is to maintain the balance between the nutrients necessary for the crops and those supplied because a small imbalance in nutrients can lead to soil depletion or over-fertility.

In this work, an integrated system comprising intensive livestock and agriculture is compared with traditional systems, from various points of view, economic and environmental. A mathematical optimization framework is developed including models for estimating energy and nutritional requirements of beef cattle, for waste treatment (anaerobic digestion), to recover nutrients, and for the management of crops. This integrated model allows relating the formulation of the diet of the animals with the composition of their feces, the necessary cultivation area (13 different crops are considered), required raw materials (water, chemicals, additional fertilizer, energy, supplements, etc.) as well as carrying out the economic and environmental evaluation of the entire system. Through the application of the model to a representative case study where the complete 6-year life cycle of 1000 calves is studied, a 49% reduction in the environmental impact of the combined agriculture-livestock system has been achieved with an economic benefit 4.7 times larger than the decentralized case, showing that not only integrated systems are economically viable but also that the environmental impact of two of the most polluting economic activities carried out by human beings can be reduced, making a correct formulation of the feed and optimal crop selection. Besides, the nutrients recovered represent 17% of Nitrogen, 5% of Phosphorous, and 26% of Potassium with respect to the necessary nutrients.

Acknowledgement

The authors acknowledge JCyL for a Ph.D. fellowship. M.L.C.

References

Edgar Martín-Hernández, Gerardo J. Ruiz-Mercado, Mariano Martín (2020). Model-driven spatial evaluation of nutrient recovery from livestock leachate for struvite production, Journal of Environmental Management, Volume 271,2020,110967,

FAO. (2006). La ganadería amenaza el medio ambiente. http://www.fao.org/newsroom/es/news/2006/1000448/index.html (accessed March 18,2020)

Gopi Krishna Kafle, Lide Chen, Comparison on batch anaerobic digestion of five different livestock manures and prediction of biochemical methane potential (BMP) using different statistical models. Waste Management, Volume 48,2016, Pages 492-502.

IPCC (2014): Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.

Kersbergen, R. Integrating Livestock with Crop Production Yields Benefits for Both. https://mosesorganic.org/farming/farming-topics/livestock/integrating-livestock-with-crop-%20production%20/ (accessed March 18,2020)

Kersberguen,R. Integrating Livestock with Crop Production Yields Benefits for Both. https://mosesorganic.org/farming/farming-topics/livestock/integrating-li... (accessed March 18,2020)

Lammel,J.(2001). Mineral Fertilizer in the Future– Sustainable Farming. https://arablefarmer.net/fileadmin/_migrated/content_uploads/mineral_fertil.pdf (accessed March 18,2020)

Oltjen, J. W., & Beckett, J. L. (1996). Role of ruminant livestock in sustainable agricultural systems. Journal of Animal Science, 74(6), 1406. doi:10.2527/1996.7461406x

Reddy P.P. (2016). Integrated Crop–Livestock Farming Systems. In: Sustainable Intensification of Crop Production. Springer, Singapore. https://doi.org/10.1007/978-981-10-2702-4_23

Xiaohui Lei, Norio Sugiura, Chuanping Feng, Takaaki Maekawa (2007).Pretreatment of anaerobic digestion effluent with ammonia stripping and biogas purification. In: Journal of Hazardous Materials, Volume 145, Issue 3, Pages 391-397,