Livestock manure is a resource that can be an asset to your farming operation if it is used and managed appropriately. However, if not carefully managed to minimise odour, nutrient losses and emissions, it can become a source of pollution and a threat to aquifers and surface waters.
By Maile Matsimela
Fanie Vorster from the Agricultural Research Council – Institute for Agricultural Engineering advises that one of the methods of using animal manure as fertiliser, is to apply it in a liquid form to crops. This, he says, can be applied to large scale and small-scale farming operations engaging in either intensive or extensive animal husbandry practices.
Vorster explains the scale of the animal farming operation and whether it is an intensive or extensive operation have an influence on the approach being followed in using the manure water for irrigation.
In intensive animal farming operations, there exists the potential for animal manure water to supplement and in some cases, even replace the inputs of commercial fertilisers. To derive the full benefit of animal manure water, while ensuring no environmental pollution, it is very important that the whole system, which includes storage, treatment and disposal, is designed properly and managed effectively.
The manure produced by the animals is washed away at regular intervals into a specially designed pond or preferably two linked ponds, where it is anaerobically stabilised before it is used for irrigation.
The volumes of manure water from specific animal housing systems depend on the cleaning method used. It will determine the percentage solids in the manure and the total volume of water flowing from the system. The large volumes of manure water can pose a problem to the environment unless they are disposed of properly.
Key Factors for Successful Implementation
Vorster said the main factors to consider when irrigating with animal manure water are:
- water quality
- soil characteristics
- hydrological factors
- climatic factors
- hydrological factors
- environmental factors
- availability of irrigation water
Water analysis, he said, is essential for effective manure water management and application.
“The correct interpretation of the water quality with which the irrigation is to be done is very important in the entire planning and management processes.
“The water quality influences the growth of the plants, soil characteristics, biological balance in the soil and it also has an influence on the irrigation equipment used,” says Vorster.
Regarding the soil, Vorster said a proper soil analysis is very important for the efficient management and application of manure water.
“The soil is the natural storage place of all plant nutrients. Soil is also the receiver of various waste products, which causes its breakdown or binding and results in the incorporation thereof into the natural cycle. Soil is the most important element in recirculation in the environment and the natural cycle,” explains Vorster.
About the hydrological factors, Vorster highlights that the topography of the area where the facility is to be erected, the climatic factors, distances from open water streams, possible positions of storage facilities and soil type, play an important role.
“The construction of the stormwater control system is necessary to control runoff that can occur during rainstorms and keep it out of manure dams. The manure dams must be prevented from overflowing of into streams and rivers.”
On climatic factors Vorster shared that the factors that play a role are total rainfall, rainfall intensity, rainfall distribution pattern, evaporation, prevailing temperatures and prevailing winds.
“The total rainfall determines the volume of water that must potentially be handled by the manure dams or leaching of salts that will occur because of the rain. The rainfall distribution pattern will have an influence on the hydrology and the irrigation management. Evaporation has an influence on the rate at which the biological breakdown takes place in the manure dams and therefore also on the possible odour problems. Evaporation is a factor that plays a role in the rate at which the salt concentration in a manure dam increases,” Vorster explains
Regarding environmental factors, Vorster says the closeness of urban or built-up areas and the prevailing wind directions play a definite role in the planning of waste handling facilities. “The question of fly nuisance and bad odours must also be kept in mind if the facility is close to an urban area.”
He went on to mention that the availability of irrigation water to ensure the irrigation of crops and for the dilution of manure water must be determined.
“If the water source is a storage dam, a water balance can be necessary to ensure irrigation throughout the year.”
Concerning the health regulations, Vorster advises farmers to consult with the local authorities regarding the health regulations to determine what the relevant requirements are. “It is very important to adhere to it, especially regarding the irrigation of edible vegetables and crops with manure water.”
Irrigation Equipment
When it comes to the actual irrigation equipment used, Vorster advises as follows:
- If an ordinary sprinkler irrigation system is used it is important to ensure that there are not any solids that can block the nozzles.
- Big gun irrigators and Travelling irrigators are good choices for applying the manure water. They can be fitted with large rubber nozzles (19mm-51mm diameter) that can handle larger solids without blocking.
- Conventional centre pivots. The manure water must be free from solids, to prevent blockages.
- Specially adapted centre pivots fitted with sprinklers with larger nozzles to be able to handle manure water with larger solid particles.
- The minimum size pipe that is suitable for the transportation of the manure water and prevention of blockages is 50mm.
- Aluminium pipes can be vulnerable to chemical reactions with the manure water. However, if the irrigation system is flushed with clean water after every application of manure water, no corrosion problems would occur.
For more information on this topic, email Fanie Vorster at vorsters@arc.agric.za.
Source: ARC – Institute for Agricultural Engineering.
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