Large-Scale Livestock Nutrient Recycling:
A Key Part of a Sustainable Nutrient
Management Strategy

Bruce T. Bowman
Former Chair, CARC Expert Committee on Manure Management
May 20, 2004

Ideas and opinions expressed in this document are those of the author and do not represent the official position or policies of any organization. This document is a work-in-progress and will be updated from time to time.

The purpose of this document is to stimulate discussion on this important issue. If you have any comments or suggestions, please forward them to Bruce Bowman

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Since World War II, the availability of relatively cheap mineral fertilizers has been a major factor spurring specialization of production agriculture, in which crop (cereal) production has been increasingly separated from livestock production. One important consequence of this has been the stranding of large amounts of nutrients in livestock manures that originated from cereal production, but which are not recycled back to the source for the next production cycle. Equally large amounts of nutrients from cereal production are also stranded within the human food chain, and frequently dumped into landfills as waste. In the longer term, these are not sustainable practices. Another concern of “livestock-free” cereal production is the lack of organic carbon being recycled to those soils, which has long term implications for soil organic matter (quality) maintenance.

In many parts of the world, phosphorus is considered a non-renewable resource, with current supplies of high quality phosphates likely to become limiting within the next 25 years, partially a result of increasing environmental issues linked to phosphate mining (water table protection and fluoride byproducts) which may limit accessibility to deposits, resulting in greater instability in phosphate fertilizer costs. Likewise, the cost of producing synthetic nitrogen fertilizers from atmospheric sources is continually increasing because of the dependence on natural gas, while also having its own environmental impacts (high energy consumption, greenhouse gas emissions). Both of these issues may result in increasing the demand and value of livestock manure nutrients.

Recent studies in the USA on whole-farm nutrient balances (budgets) have demonstrated that a large proportion of the farms studied have substantial nutrient excesses (INPUT/OUTPUT > 1.5), especially for nitrogen (Koeslch & Lesoing, 1999; Cogger,1999; Nord & Lanyon, 2003). On-farm nutrient excesses can be addressed in three ways:

  1. Reduce nutrient inputs to balance nutrient exports from the land base,
  2. Increase the land base for applying [manure] nutrients (buy, rent more land or, contract with neighbouring farms to receive excess manure; Exporting liquid manure nutrients is usually limited (economically) to an area around the farm having a radius less < 15 km), and
  3. Export excess nutrients from the farm in the form of value-added products.

Farmers will need increased flexibility in managing nutrient budgets and on-farm nutrient excesses, as more stringent nutrient management and source water protection legislation are implemented across Canada.

It has been calculated that,

In the 20th century, human interference in the nitrogen cycle has caused a doubling of the global nitrogen fixation rate, thereby intensifying global nitrous oxide (N2O) production during microbial nitrification and denitrification” (Barton and Atwater, 2002).

Thus, it will become increasingly imperative that ways be found to facilitate the large-scale recycling of nutrients (livestock and human food chain) to reduce the annual tonnage of new mineral fertilizers required for crop production.


Facilitating large-scale nutrient recycling

There are three key criteria to be met in facilitating large-scale nutrient recycling - the manure must effectively be:

  1. Odour-free,
  2. Pathogen-free and
  3. Dewatered (not economic to transport water).

In effect, manure must be processed (treating the entire manure volume) to achieve these objectives. Achieving these goals also solves the major environmental and societal issues surrounding modern day livestock production (odours, and water quality issues - nutrients and pathogens). The impact of societal concerns on the livestock industry should not be under-estimated, and if ignored will result in the transfer of significant livestock production capacity to areas of the world with cheaper labour rates and more lax environmental protection (e.g. Eastern Europe or South America).

There are two primary methods for processing the entire manure volume at farm-scale: anaerobic digestion (AD) or composting, depending on the nature of the farm operation. Although composting is by far the cheaper of the two solutions to implement, there are some potential disadvantages to composting (substantial ammonia-N losses, and potential greenhouse gas emissions). Pre-adjusting the pH of the solid manure to near neutrality (pH 7), may substantially reduce ammonia-N losses during composting, and keeping the piles aerobic will minimize methane or nitrous oxide emissions.

In anaerobic digestion systems, processing is confined to closed vessels which virtually eliminates nutrient or greenhouse gas emissions. There is an increasing potential for reasonable payback with increasing markets for biogas-generated electricity, which can make a measurable contribution to the renewable energy base. Unlike some other renewable energy sources (wind, solar), AD-generated electricity from livestock wastes is a 7/24 operation that contributes to baseload capacity for the electrical grid. It is estimated that in Ontario, there is potential of 250 MW of electricity capacity from livestock wastes, and near 1,500 MW, nationally.

The major barriers to profiting from farm-based renewable energy production are beginning to diminish as impending energy shortages loom in various jurisdictions, an example being the lack of access and the right to sell electricity back to the grid at fair market prices. The demand for farm-based renewable energy will increase substantially in the coming decade as fossil fuel reserves fall behind market demand and energy costs continue to soar.

The development of two new revenue streams for farmers - the sale of renewable energy and off-farm sale of excess nutrients - could provide a degree of income stabilization for them, since animals continue to produce manure regardless of their commodity values!


Making large-scale nutrient recycling successful

In order to facilitate large-scale nutrient recycling, there are at least four major issues to be addressed;

  1. Health/Safety (pathogen-free);
  2. Ease of Use;
  3. Competitive with other nutrient sources, and organic carbon, and;
  4. Easily accessible to the end-user.

As discussed above, there are several other contributing factors driving the manure processing issue, which also address the health and safety issue. Furthermore, both product development (e.g. pellets, granules, other) and distribution networks need to be developed to ensure that these value-added organic amendments/fertilizers are available at the local “nutrient supplier” (fertilizer dealer), and in a form that can be bulk blended with mineral fertilizers for easy application with existing equipment.

It may be necessary to implement policy incentives in the early stages of developing this value-added nutrient recycling industry. In some European jurisdictions, environmental taxes on mineral fertilizer usage are being implemented as a means of controlling nutrient loadings in the environment. In North America, consumers paying a premium when buying organic produce are, in effect, paying an environmental tax in support of production methods that are perceived by the public to be more environmentally friendly.


Related Nutrient Use Issues

  1. Biological Nutrient Removal
    There are a number of technologies being developed with the express purpose of reducing excess nitrogen levels in a particular system by “biological nutrient removal”, which involves the oxidation of ammonia/ammonium-N to nitrate or nitrite, followed by reduction to atmospheric N2 (Vanotti and Hunt, 1998). Purposely exhausting fertilizer-N to the atmosphere is not a sustainable practice and should not be adopted, since replacement fertilizer-nitrogen must be re-captured from the atmosphere, consuming additional natural gas and creating more greenhouse gas emissions. Wastewater lagoons and constructed wetlands may also enhance the reductive removal of nitrogen back to the atmospheric N2 form.
  2. Incineration of Livestock Manures
    In several regions of North America, incineration technologies for solving excess manure nutrients are now being seriously considered (various Canadian Provinces), or already being implemented (Delmarva Penninsula and North Carolina, USA). In most cases, the soils in the regions surrounding high-density livestock operations (often poultry), have become saturated with over-applications of phosphorus resulting from insufficient land base, while the value of those manures is insufficient to transport it beyond that immediate region.
    Unless there are issues involving “specified risk materials”, such as BSE-infected livestock, incineration solutions should be used only as a last resort. In general, all of the nitrogen is lost back to the atmosphere, and depending on the incineration procedure used, the remaining ash, containing phosphorus and other nutrients, may not be recycled for further agriculture use. A more sustainable solution to the excess phosphorous problem would be to anaerobically digest the manure to generate biogas and electricity, then dewater the digestate to produce a high quality organic amendment or fertilizer. In general, organic carbon originating from crop production should be returned to the soil for future production cycles, and not short-circuited by exhausting CO2 to the atmosphere during incineration, thereby increasing the warming potential of the atmosphere.



Large-scale livestock nutrient recycling is the key “other half” of the equation in a sustainable nutrient management strategy. Nutrient managing planning at farm-scale will tell us how efficiently we are utilizing our nutrient sources, and should lead to improvements such as rations which lower nutrient inputs while increasing nutrient use efficiency. Livestock nutrient recycling will provide the farmer with needed additional flexibility to readily export excess nutrients back to where they can be re-used in the next cereal production cycle, thereby reducing nutrient loadings and potential risks of water contamination on the farm.

Developing a viable livestock nutrient recycling industry will help extend the finite reserves of existing phosphate sources, and reduce the environmental impacts from continually replacing “leaked” nitrogen with new fertilizer production. Practices need to be encouraged that keep both nitrogen and phosphorus in the recycling loop. Unless nutrient loadings in the environment are managed in a more sustainable manner, it will be difficult to maintain current water quality standards in the long term.



Barton, P.K. and J.W. Atwater. 2002. Nitrous Oxide Emissions and the Anthropogenic Nitrogen in Wastewater and Solid Waste. J. of Environ. Eng.128: 137 - 150.

Cogger, C.G., T.N. Cramer, A.I. Bary, and D.C. Grusenmeyer. 1999. Whole Farm Nutrient Flow and Manure Management  [33 KB pdf]. Presentation at Northwest Dairy Shortcourse, Blaine, WA.

Koelsch, R. and G. Lesoing. 1999. Nutrient Balance on Nebraska Livestock Confinement Systems. J. Anim. Sci. Vol. 77, Suppl. 2/J. Dairy Sci. Vol. 82, Suppl. 2.

Nord, E. A. and L. E. Lanyon. 2003. Managing Material Transfer and Nutrient Flow in an Agricultural Watershed. J. Environ. Qual. 32:562–570.

Vanotti, M.B, and P.G. Hunt. 1998. Ammonia removal from swine wastewater using immobilized nitrifiers.  



Bruce T. Bowman, Archivist
Last Updated: Saturday, October 06, 2018 03:44:29 PM