Animal waste is not something exciting to monitor on a regular basis. It can therefore easily accrue to unmanageable levels before anyone notices. This month we look at different methods to handle sheep waste. We thank the ARC Institute for Agricultural Engineering in South Africa who made their manual on sheep production and facilities available to the readers of ProAgri Zambia.
Systems and methods
The handling of waste has come to the fore strongly the past few years resulting from the pollution potential of waste. The direct inlet of run-off water from feedlots and intensive production systems into rivers and streams is currently prohibited by legislation and it is the responsibility of the designer to ensure that waste is handled according to the prescribed norms and standards. As production systems are intensified, stricter legislation is expected. The correct handling of waste will not only decrease potential pollution, but also diseases and unpleasant odours.
Figure 1 shows a diagram of how waste is handled in the different production systems. Waste handling in systems with a large component of planted crops or natural grazing, is normally not a problem, because it is already spread over a wide area. A directive to be considered here to minimise diseases and pollution, is that no waste handling measures are necessary if the area utilised as grazing is large enough to maintain vegetation. In intensive systems, waste is handled according to the lay-out of the facility.
Figure 2 shows the handling of sheep waste in an open feedlot system. In open feedlots, liquids are collected by means of a run-off control system, after which the solids are separated from the liquids in a sedimentation dam.
Sedimentation dams are usually shallow structures lined with concrete to simplify the maintenance and cleaning process. The inlet to the sedimentation dam is bevelled to a fall of ± 10% to make access for a tractor possible. See figure 3.
The filter can be made of ordinary rectangular bales that hold back the solids and let the water seep through. As the effectiveness decreases, the bales are removed and replaced by new ones. The filter can also be a stone stratum consisting of a mass of small round stones that retains the solids and lets the water flow through. The stones must be sprayed clean regularly to prevent blockage.
The liquid flows from the sedimentation dam to a storage dam where it either evaporates or is pumped out by an irrigation system or other distribution methods onto nearby fields. Alternatively, the liquid can be led away to an infiltration dam or a vegetated area to evaporate or infiltrate there. The solids are immediately spread onto the nearby fields or stored in heaps for composting or later distribution. Maize cobs covered with a layer of straw can be used as a basis for the dung heap.
Directives for waste handling systems:
The infiltration dam in which the water is accumulated must be at least 100 m long and preferably have a slope of about 0,25%. The infiltration tempo of the region will decrease drastically with time and can cause problems if sedimentation dams are not used to remove solids beforehand.
The use of infiltration dams are only recommended for production systems with fewer than 750 animals. Alternatively, water must flow into storage dams and be sprayed out onto fields.
The slope of the first 20 m of the run-off control system must be approximately 4% to achieve run-off from the housing complex as soon as possible and to prevent deposit of solids in the canals. The slope can then be graded to approximately 1% to the sedimentation dam.
The size of the sedimentation dam can be calculated from:
~ surface approximately 1/40 of the total feedlot area.
~ volume 0,15 to 0,3 m3 for each 10 m2 of the feedlot surface
(These values can be smaller in regions with a low to very low rainfall).
More general and design information and directives are given in the manure handling manual of the ARC-ILI.
Next month we shall look at feed handling and distribution.
Published with acknowledgement to the ARC Institute for Agricultural Engineering for the use of their Sheep Facilities Manual. Visit www.arc.agric.za for more information.