The value of animal waste is grossly underestimated. In Europe, animal waste was intensively used as fertiliser before the Second World War. The advent of reasonably cheap, inorganic fertiliser as a by-product of the production of explosives, diminished the use of animal waste. In the current world situation of expensive commercial fertilisers, the attention is again shifting towards the use of animal waste as fertiliser.

This month we take a look at waste production, the benefits it offers to a farmer, and how to control it. 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.

Animal waste is rich in plant nutrients and can be used successfully as fertiliser. Approximately 50 to 70% of the total nitrogen intake and 60 to 80% of the phosphorous intake of animals are excreted in the waste.

The nitrogen occurring in the animal waste, however, varies in plant availability and occurs in a number of chemical compositions of which ammonia (NH³) constitutes about 60%. The plant’s available nitrogen is approximately 30 to 70% of the total nitrogen present in animal waste. The relatively low values occur in solids, while higher values refer to the plant available nitrogen in the liquid portion of the excretions.

The amounts of phosphorous (P) and potassium (K) which occur in the waste as plant available links, compare well with that of commercial fertilisers. It has been further established experimentally that P derived from animal waste increases the total plant available P in the soil in comparison to the situation where only commercial fertilisers are used.

Other benefits of the use of animal waste as fertiliser include:

• The favourable influence on trace elements in the soil.

• The improvement of the ion exchange ability of the soil.
• The improvement of the soil structure which determines, among others, infiltration, water retention ability and arability.

Table 1 and 2 show the specific composition of excretions of sheep.

A sheep produces approximately ¾ to 1 tonne of waste per year. If we accept a production of ¾ ton, the financial value of the waste can be calculated per element.

Waste production of sheep

The daily waste production for sheep is approximately 30 to 40 kg / 1000 kg live mass per day.

A detailed version of waste production is shown in Table 3.

Utilisation and distribution of waste

Ineffective utilisation of animal waste as fertiliser can lead to serious environmental pollution. Ammonia emission is one of the factors responsible for soil acidifying. In regions with concentrated intensive animal production systems, the problems of air pollution and soil acidification can cause great damage.

The pollution of water by the leaching of mainly nitrates, increases the nitrogen content of the water. The increased nitrogen content gives rise to an oxygen shortage in the water and stimulates the growth of algae, which causes great damage to the fine balance of eco-systems of river and marsh areas.

The greatest losses experienced during the use of animal waste as fertiliser, is the loss of nitrogen through ammonia emission or the nitrification process (the biological oxidation of ammonia nitrogen to nitrate and nitrate.

The following directives must be kept in mind:

• Apply in spring directly before planting or sowing of the relevant crop. The synchronisation of availability of fertilisers and the requirement of plant nutrients as well as the relatively low soil temperatures decrease the losses resulting from leaching and nitrification.
• Application should preferably be done subsurface (plough directly after application). Losses resulting from nitrification is limited in this way.
• If waste is stored in heaps for later distribution, the exposed surface of the heap must be as small as possible. This not only decreases losses in nutrients, but it also limits unpleasant odours. It is important to obtain expert advice and to analyse the soil, water and manure before fertilisation by means of animal manure is done on a specific soil type for a specific crop.

Control of unpleasant odours

Unpleasant odours caused by skatole (C⁹H^9N) in manure may evoke public complaints and are annoying in the living and working environment. Although legislation does not currently exist for allowable emission of odours, it can be expected in the future, as research progresses to quantify the concentration, intensity and human tolerant values. Table 5 shows the major values and contributions of the sources for production of unpleasant odours.

Methods of controlling and eliminating unpleasant odours include the following:

• Correct zoning with regard to farm houses, other housing and wind directions will decrease the detection of odours.
• Biochemical additives to limit the production of gases.
• Air fresheners to limit the detection of odours
• Correct storage of waste matter
• Effective manure dams
• Tillage of fields directly after spreading
• Regular removal of manure
• Air-drying of solid waste.

Next month we shall look at the systems and methods to treat and handle sheep waste.

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.