Introduction
More than 70% of nutrients contained in livestock feed are excreted as manure and urine. In grazing and mixed crop-livestock systems, livestock tend to consume grasses and farm residues, returning a significant portion of their dietary nutrients directly to the soil while roaming and grazing, or through active manure collection, storage, and application.
In intensive systems, which often decouple livestock from land, large concentrations of manure — and nutrient — can, however, build up where animals are raised, away from the feed production area. This issue is amplified by the typical geographical concentration of intensive animal production units.
This fifth principle provides guidance for managing manure in a way that contributes to soil nutrient balances, while generating multiple environmental and economic co-benefits. It has particular relevance for intensive pig and poultry systems, which tend to confine animals indoors.
Coupling livestock to land underpins long-term agricultural resilience.
In livestock-producing regions, nitrogen, phosphorous, and other nutrients contained in manure may evaporate or leach into the environment and impair soil fertility; cause freshwater eutrophication; and damage ecosystem health. In feed-producing regions, the loss of soil nutrients embedded in feed exports may, over time, result in soil nutrient depletion and jeopardize soil fertility. “Coupling” livestock to land or managing nutrient flows from livestock production to improve local and global nutrient balancing thus strengthens the natural resource base on which long-term agricultural resilience depends.
Managing manure such that it can be used to fertilize crops and grasslands can contribute significantly to nutrient balancing. The organic matter in manure also enhances the capacity of soil to absorb and retain water. Integrated manure management is a recommended approach that requires attention to the entire manure chain: collection, treatment, storage, and application. Through the processing and marketing of transportable manure products to complement or replace synthetic fertilizers, manure recycling can contribute to nutrient balancing at both local and global levels.
Importantly, adequate land/livestock balances will minimize the need to transport manure out of livestock concentration areas and thus reduce manure management costs.
Points of Consideration:
Does the project confine animals indoors? If so, in project design, ensure adequate manure management along the entire manure chain:
✓ Estimate the project impact on nutrient flows:
- Quantity of manure to be produced.
- Nutrient content of the manure.
- Nutrient absorption capacity of local crops and grasslands (on-farm,
within financially viable transportation range).
✓ Link to local nutrient flows and demand for organic fertilizer:
- Application of fresh manure.
- Manure composting.
- Anaerobic digesters.
✓ Link to regional nutrient flows and demand for fertilizer:
- Manure drying and export (pellets, granules).
✓ Include a baseline and indicators in project M&E to track and capture the benefits of enhancing nutrient cycling through the project.
Approaches and Tools:
Estimate the project impact on local nutrient flows. Selection of an appropriate manure management system will depend on the estimated quantity of manure to be produced; the nutrient content of the manure; and the capacity of the local land base to absorb these nutrients. These figures can be derived through standard values or site-specific sampling of livestock manure excretion, manure nutrient content, and soil nutrient levels in crop- and grasslands.
Consider local and regional/global demand for manure as organic fertilizer. Where there is demand for manure as fertilizer, livestock producers may design manure systems that link to local crop production and grassland management. Conducting a cost-benefit analysis of using manure as organic fertilizer in place of and/or compounded with synthetic fertilizers may help stimulate local demand and build a market for manure products. In addition, producers may explore producing transportable manure products and linking to regional/global fertilizer demand.
Options for linking to local crop- and grasslands:
Application of fresh manure. Manure can be collected manually, stored, and applied fresh to crop- and grasslands as fertilizer (FAO, 2015a). While solid manure can be collected through shoveling or other forms of manual labor, collecting liquid manure or “slurry” may require flushing with water into pit storage and pumping into distribution pipes or tanks for transport. Fresh manure is often too heavy and wet for long transport to be efficient.
Production of compost. Composting generally entails collecting, storing, and processing manure over time, together with plant material, into decayed organic matter. For easier integration with solid manure, slurry may be mixed with bedding, wood shavings, or other dry material. Recommended composting techniques depend on the climate, available space and time, and hygienic safety, generally ranging from closed systems maintained indoors in containers to open systems consisting in outdoor piles (FAO, 2015b).
Anaerobic digesters. Anaerobic digesters or “bio-digesters” are covered pits or tanks in which bacteria convert organic waste, such as manure, into methane biogas through anaerobic digestion. Small-scale digesters are often used to power off-the-grid households, and large-scale digesters can fuel electric power generators. Electricity may be used on farm use or fed to the grid. The nutrient content of the liquid digester effluent or “bio-slurry,” while often overlooked, is similar to the content in the original manure (gases generated through the digestor contain marginal amounts of nitrogen, phosphorus, and potassium). Digestor outflows must thus be stored and applied according to a nutrient management plan, as for fresh manure and compost.
Options for linking to regional/global fertilizer demand:
Manure pellets and other dry products. Manure products with low water content are most cost-effective for longer transport and export. These include pellets and granules produced through processing and drying manure at high temperatures (Wageningen, 2014). Challenges to manure product export may include difficulty in meeting health standards for trade in animal by-products.
Variables to Consider:
✓ Nitrogen and phosphorus surpluses (often expressed per ha) at different aggregation levels (plot, farm, watershed).
✓ On farm and/or regional nutrient and organic matter management plans.
Trade-offs
Potential for overfertilization. Integrating manure into crop- and grassland fertilization without evaluating the nutrient balance can result in overfertilization. Identifying where the introduction or expansion of manure recycling may imply reductions in the use of synthetic fertilizer will help avoid this outcome.
De-prioritization of synthetic fertilizer economy. While the benefits of organic soil amendments are broadly known (FAO, 2015a), producers of synthetic fertilizers are, in many regions, significant private sector stakeholders in agriculture. Effective promotion of recycling manure as fertilizer may require economic and policy planning to reduce market barriers for manure products and ensure equal access to subsidies and other public support.
Limited suitability for livestock production. In some regions, the limited availability of crop production and/or grassland on which to apply increased amounts of manure may lead to evaluating whether the project site is suitable for expanding intensive livestock production. Teams may seek alternative locations for livestock development, where land/livestock balances are more favorable.