Sustainable Nutrient Management in Agriculture and Closing the Loop on Large-Scale Nutrient Flows
Bruce T. Bowman
In both types, the loop on nutrient flows (recycling) back to the source is frequently severed, resulting in large-scale regional nutrient accumulations in some areas while there are nutrient deficits in other areas.
Nutrient flows can be defined as:
This document focuses on the first part of the definition.
A. Nutrient Flows through Livestock Operations
Specialization and intensification in modern production agriculture has fostered the proliferation of farm operations focussing on either cereal production or on livestock/poultry production, resulting in fewer integrated farms with both crop and livestock production. There are several important consequences resulting from this trend:
Strategies for Closing the Loop on Nutrient Flows through Animal Production Systems
There are extensive areas of farming operations where cereal production and livestock production are separated. There are at least two possible strategies to improve this situation:
Encourage the establishment of integrated livestock-cereal production farms (new operations or conversion of separated operations) where recycling animal nutrients back to the land would be the normal practice. One approach might involve government intervention through policy changes, such as incentive programs, that would make integrated farms more sustainable (economically, environmentally, socially), relative to specialized cereal or intensive livestock operations.
This would have been a more viable option for pork and beef producers when there were many small abattoirs scattered throughout the countryside that could support a distributed livestock production system on integrated farms. However this option is now becoming much less feasible because very few, high capacity packing plants are operating close to existing high-density livestock operations. Corporate livestock operations, which are starting to dominate livestock production in various parts of North America, prefer to concentrate their livestock operations near these large packing plants to minimize shipping costs and reduce transportation stress on the animals.
This integrated farming approach may be more amenable for dairy farms, where fluid milk products can be shipped considerable distances for processing and distribution. Cereal-only farms remain the only viable option in some semi-arid regions, such as regions in the western prairies of North America, where there are insufficient water supplies (quantity or quality) to support livestock production.
Develop practices that can effectively recover [excess] nutrients from livestock operations and recycle them back to existing cereal production farms. This approach would capture and recycle excess nutrients from livestock manures by producing consistent, concentrated organic fertilizers, which could be economically transported back to cereal-based farms, and compete with the existing practices of using only non-renewable mineral fertilizers.
A key to this approach is the treatment of livestock wastes, de-watering the manures and converting them into granules or pellets that can be easily (economically) stored, transported considerable distances (same as for mineral fertilizers) and applied using standard fertilizer application equipment. These organic amendments, besides containing nutrients, will also improve soil quality, unlike their mineral fertilizer counterparts. It may be economically feasible to fortify these organic amendments with additional nutrients to guarantee a specific nutrient content that could be sold as organic fertilizers under the Fertilizer Act.
The manure treatment process, if using a closed vessel treatment system, can also solve most of the odour and pathogen problems currently plaguing the livestock industry, reduce greenhouse gas emissions in the storage and handling phases, and provide the farmer with greater flexibility in managing excess nutrients in the livestock operation.
A second key element driving this option would be the development of the necessary business infrastructure to transport, store and distribute these organic fertilizers, much in the same fashion that agro-marts currently market mineral fertilizers. A necessary part of this process would be the production of consistent quality products with a clear market advantage over mineral fertilizers could be established.
B. Nutrient Flows through Human Foods
There is a second large-scale nutrient flow loop involving human food consumption that, for the most part, has also been severed. Nutrients in foods for human consumption are exported directly from cereal production areas, and indirectly to human use from animal production through milk, meat and poultry products (see Figure 1). According to Barton and Atwater (2002), 25% of agriculturally-applied nitrogen leaves the farm in food products. Nutrients from these sources tend to be disposed of through sewage systems, landfilling, incineration, and to some extent through biosolids, some of which may be recycled to agricultural production lands. Included in this group are considerable amounts of nutrient wastes from food terminals, the fast food industry, and other vegetable/food processing activities.
Since about 75% of Canada’s population resides in the 5 largest cities in Canada, recycling human waste and correcting that nutrient balance has become incredibly important. Efforts need to increase to capture these valuable sources of nutrients and organic matter and to recycle them to crop production areas. There are, however, several existing barriers that have limited the recycling of urban food-sourced wastes, including:
In order for society to move towards more sustainable use of nutrients, there are two anthropogenic nutrient flow loops that need to be closed, one primarily through production agriculture, the other through human food production and consumption.
1. Agriculture needs to close the loop on large-scale nutrient flows through livestock production systems, which are not currently being recycled back to crop production areas. Current fertilizer use practices place too much reliance on non-renewable mineral fertilizers for crop production. The continuing influxes of large annual amounts of "new" mineral nutrients from natural mineral deposits into crop production systems further increases global risks for water contamination by nutrients. This practice is unsustainable in the long term, making it virtually impossible to maintain current water quality standards. Increasing the use of recycled organic fertilizers will help stabilize global nutrient levels in the environment, while also having an important soil-building (soil quality) aspect that mineral fertilizers lack. In fact, extensive, continued use of mineral fertilizers will decrease overall soil quality.
In the livestock production nutrient flow loop, two possible solutions include:
2. The issue of closing the loop on nitrogen flows from agriculture to urban areas is a much broader societal problem requiring new partnerships and infrastructure to be developed between agriculture and municipal/urban entities. One key component to the success of closing this loop will be separating the heavy metals and other toxic contaminants from the human waste stream, so as to make recycling human wastes safe for land application in agricultural production areas.
Other related information
Land Spreading of Animal Manures, Farm Wastes & Non-Agricultural Organic Wastes, Part 1: Manure (and Other Organic Wastes) Management Guidelines for Intensive Agricultural Enterprises; Owen T. Carton1 and William L. Magette2. 1Teagasc, Johnstown Castle Research Centre, Wexford; 2Dept. of Agricultural and Food Engineering, UCD, Earlsfort Terrace, Dublin 2. May 1999; ISBN 1 84170 23 8
Nitrous Oxide Emissions and the Anthropogenic Nitrogen in Wastewater and Solid Waste. 2002. Philip K. Barton and James W. Atwater. J. of Environ. Eng.128:137 - 150.
Bruce T. Bowman, Archivist