Negative and positive aspects of manure are closely interrelated because emissions at an early stage inevitably have repercussions on positive effects on the soil and any crops at a later stage. This is schematized in Figure 1. The amounts of nutrients sucgh as N, P and K taken up by the crop determine the agricultural value of the manure and depend on the amounts of nutrients emitted during the path from animal to crop. The greater the nutrients loss the lower agricultural value of the manure.
 

Figure 1 Possible nutrient losses from manure between excretion and crop uptake. Source:  redrawn from Brandjes et al., 1996. Click on the figure to view a larger version

Techniques

The manure management systems are highly diverse:

• Grazing: natural distribution of feces on pastures. Substantial losses through leaching due to the uneven distribution of feces and urine. Volatilization of part of N.

• Corralling (kraals): Often used as in situ fertilization of arable land by moving the kraal regularly. Soil nutrients of a larger area used for grazing are recycled and concentrated on the crop area, enabling production in resource-poor situations.

• Dry lot storage: Urine is not collected and bedding is sparsely used. Losses of N and K are high as most urine is lost. Part of the nutrients of feces are lost by leaching and surface runoff in the case of high precipitation and uncovered manure heaps. Using bedding can capture a part of urine by absorption and reduce losses.

• Slurry storage: Feces and urine are stored together. Commonly used in intensive livestock systems in OECD countries. Volatilization losses are dependent on the storage depth and time.

Lagoons: Liquid manure, either before or after separating parts of the solids, is treated in anaerobic lagoons. Organic material is decomposed, thereby mineralizing part of the nutrients. The liquid phase is either discharged into surface water or used for irrigation.  Emission of NH3, CH4 and N2O. [See also: Greenhouse Gas Emission]

The photo shows storage of manure in a lagoon  - without any lining and without any cover

• Fuel: in several developing countries, manure is collected and dried to be burned as a domestic fuel. Most of the N, C and S will be lost during combustion. Other nutrients may be recycled to arable land via the use of ash.

• Feed: manure could be recycled to feed (livestock and fish), but this practice is limited. Only poultry manure is of a reasonable quality. Animal manure is recycled in integrated fish production in Asia (see Integrated fish production).

All livestock production systems are concerned, but industrial systems are the most implicated because of the large amount of manure produced. The mixed systems generally include processing and utilization of manure in farming procedures.

Grazing System

LGA	LGS1	LGS2	LGS3	LGH1	LGH2	LGH3	LGT1	LGT2	LGT3
y	y	y	y	y	y	y	y	y	y

Mixed System

MCG	MCR	MCC	MFF	MEF
y	y	y	y	y

Industrial System

IFP	IPL	IPG	IRM	IDU	ISL	ITN	IMP
Y	Y	Y	Y	Y	Y	Y	Y

Impact

Positive environmental impact

• Soil fertilization by manure application : decomposition of the organic material by microorganisms produces carbon dioxide (CO2), water and minerals of plant nutrients as N, P, S and metals. The mineralization is the transformation of organically bound elements into plant available nutrients. Application of manure to crop land or pastures will reduce the requirements of artificial fertilizer.
• Soil fertility improvement : organic matter that remains one year after application is assumed to be part of the soil organic matter and will decompose gradually over the years, releasing plant nutrients.
• Improvement of the soil structure stability. Organic matter is also involved in the physical properties of soil e.g. porosity, aeration waterholding capacity, it improved soil structure and reduces the soil vulnerability to erosion.
• Improvement of inorganic fertilizer potentiality : organic matter in soil increases the capacity of absorption of minerals, reducing the loss of the elements brought in the fertilizers. Absorbed elements are gradually released for plant nutrition.

Negative environmental impact Ammonia emissions: before and during storage, and during application in the field. Emission of NOx: this is formed as a by-product of the denitrification process. Emission of methane, formed upon decomposition of manure under anaerobic conditions. Runoff of manure and manure components into surface water, contributing to water pollution. Leaching of nitrate and phosphorus into the ground water, contributing to underground water pollution.

Overflow from manure pit onto  open water - a negative impact  of poor manure management

• Favourable factors:

In systems with nutrient deficit.
• Feeding supplement to livestock.
• Promoting corralling and feedlot.
• Extension material to promote manure transportation.
In systems with nutrient surplus :
• Getting towards a balance between mineral and organic fertilizers for crop fertilization.
• Establishing a quota for manure production.
• Limiting stocking rate in nutrient surplus areas.
• Limiting mineral fertilizers/ha.
• Taxes and duties on mineral fertilizers.
• Limiting manure storage on the farm.
• Establishing and following rules for manure application (dates and amounts).
• Subsidies for manure treatment and management, Taxes on livestock feed.
• Livestock genetic improvement.
• Open access to barn allowing production of good quality manure with straw.

• Unfavourable factors:

In systems with nutrient deficit:
• extensive livestock system producing limited quantities of manure.
• lack of equipment and labor for transport and use of manure.
• loss of nutrients in cultivated areas (minerals exported in crop products, leaching of minerals).
In systems with nutrient surplus:
• Excess of animals in comparison with soil capacity to absorb animal waste and manure.
• Import of feed for livestock.
• Preference to the use of inorganic fertilizers in place or in complement of manure.

Brandjes P.J., de Wit J., van der Meer H.G., van Keulen H., 1996. Environmental impact of animal manure management. Livestock and the environment ? Finding a balance. International Agriculture Centre, Wageningen (the Netherlands), pp. 53.

H.J.M. Hendriks and A.M. van de Weerdhof. Dutch Notes on BAT for Pig- and Poultry Intensive Lifestock Farming. August 1999. Information Centre for Environmental Licensing, P.O. Box 30732, NL-2500 GS The Hague, The Netherlands. Tel: +31 70 3610575; Fax: +31 70 3633333; Internet: “www.infomil.nl”. Click here to view document in Acrobat format.

See Also

Manure Storage