The Economic Value of Manure

In developing countries, the potential of manures - especially animal manures - is often underestimated. Organic manures include all nutrient sources derived from plant or animal origin, and represent an underestimated source of soil nutrients that can be especially valuable for smallholder farmers under mixed crop-livestock production systems. Organic manures are differ from chemical or mineral fertilizers - in particular they contain organic matter. This provides a slow and steady source of nutrients and maintains or improves the quality and structure of the soil.

The Economic Value of Manure Methods of Evaluation Markets for Manure Making Better Use of Manure References and Further Reading   See also Management of Manure Better Manure Better Crops

Manure is a natural by-product of livestock production. It has several possible uses; as an organic fertilizer, a fuel or even as a building material. Where firewood is scarce, manure may be dried and later used as a fuel for cooking fires. It is also sometimes used as a binding material in building earth walls. Poultry manure has, in a limited number of cases, been used as a feed for ruminant livestock or fish, but the nutritional value is relatively poor while there are associated health risks - for both livestock and humans. More generally manure is seen as a source of plant nutrients and organic matter to restore soil fertility.

In many extensive, mixed-farming systems in rural areas, manure is valued by farmers as an input to crop production, or for meeting other household needs. Special efforts are made to collect and save the manure. Surveys of livestock producers in developing countries generally record manure as a valuable product. A survey of 48 sites in Asia, Africa and Latin America showed a majority of farmers use manure on their crops (Baltenweck, et al. 2002). In some cases animals are penned or housed, with the specific objective of collecting the manure. Overall an estimated 70% of total fertilizer inputs, in developing countries, are derived from animal manure (Fresco & Steinfeld 1998).

The use of manure for fertilization varies within continents and between agro-ecological zones. The situation inn Sub-Saharan Africa has been studied in some detail. Within the humid zone of the sub-continent, relatively little manure is applied, other than where population density is high. Fertility may be maintained by bush fallowing and fallen vegetation. Manuring is more common in the sub-humid zone, often by paddocking livestock on crop fields. Use of manure is thought to be essential, especially for high value crops in the semi-arid and highland zones (McIntire, Bourzat & Pingali 1992).

In the densely populated humid zone of Southeast Asia manure provides much of the phosphate nutrient required for intensive rice production. It serves as a medium for the transfer of nutrients from grazing to cropped areas (de Wit et al 1997). Apart from this zone, the survey of sites in Asia and Latin America as well as Africa, showed only 20% of farmers in the humid zone using manure, while in the other zones the proportion is over 70% and over 80% in the sub-humid zone.

The value of manure, as a fertilizer, depends in part on the cost of labour, both for its transport and for its application, in relation to the value of the land and the crops that can be produced from it. Manure is more likely to be applied where labour is cheap. It is less likely to be applied where alternative cheap chemical fertilizers are available. In the case of manure produced from intensive landless production systems, in peri-urban environments, disposal often presents severe environmental problems. The manure is a costly liability rather than an asset.

 

As most manure produced on mixed farms is applied directly to crops within the same farming system, there are problems of estimating the money value of manure. Estimates are commonly based on what it would cost to provide the same quantities of plant nutrients from chemical fertilizers. However, this method can only provide crude estimates. The value of manure may in fact be much greater because the organic matter in manure provides additional benefits to soil structure and plant growth. A complicating factor is that major losses occur in storage, transport and application of manure to the soil, and this then lowers the effective value of the product.

In theory, a better measure of the value of manure would be the gain in value of the crop production per hectare derived from the manure application. However, this would require experimental trials with and without manure fertilizer application, to assess the impact.

A third alternative is to use the market price if a market for manure exists.

In regions where manure is of positive economic value, as an organic fertilizer, markets may develop where it can be bought and sold. However, its financial value is relatively low, and it is bulky and costly to transport. Despite this low value to cost ratio, there are instances of goat manure being transported over quite large distances in Bolivia, for use in potato and onion growing areas. Generally market transactions are more likely to be direct, between seller and buyer in local markets, to avoid the heavy transport costs. More readily transported sun-dried manure, is marketed as fuel in much of South Asia.

Commonly transport of manure is avoided. A commonly used system where transactions take place between livestock owners and crop farmers involves grazing of livestock on post-harvest crop remains. The livestock owner benefits from the feed resources provided, while the crop producer benefits from the manure and resultant improvement in crop production. As an example, a village study in Northern Nigeria, in the 1980s found that 50% of crop farmers paid Fulani herders to camp their animals on the crop fields (McIntire, Bourzat & Pingali 1992).

In contrast, producers of intensive livestock in urban areas may need to pay for the removal and disposal of manure.

 

Over the last half century in the developed countries, rapid growth in the use of nitrogenous and other chemical fertilizers has substituted for farmyard manure in the maintenance of soil fertility, and enabled farmers to abandon mixed crop-animal husbandry systems. It is estimated that by the late 1980s nitrogenous fertilizers provided about 50% of the total nutrient flow in global cropland, while animal wastes provided less than 9% (Smil 1991).

However, in developing countries relative prices make chemical fertilizers less attractive. Furthermore, the structure of many tropical soils is poor and therefore likely to benefit from application of farm yard manure even where fertilizers are also used. Hence manure is likely to remain an important input to crop production for long into the future, even though increasingly supplemented by chemical fertilizer.

The value of manure, as a fertilizer, may be increased by composting with additional plant material. In semi-arid conditions, a much greater increase in crop production is obtained when manure is used in combination with rainwater harvesting, for instance using planting pits or contour bunds. (For more information on composting see Misra et al. 2003)

The value of manure, as an energy source, can also be enhanced through biogas production. On farm bio-digesters can play a vital role in integrated farming systems by reducing pollution and adding value to livestock excreta. Not only is the gas a more convenient source of energy than raw manure, but the residue from the biodigester may still be used to provide soil nutrients. However, the efficient management of biogas slurry is complicated and the costs can only be justified where other sources of domestic gas or electricity are lacking. most small-scale biogas generators tend to make use of zero-grazed dairy cattle, rather than smallstock.

Lekasi, J.K., Tanner, J.C., Kimani, S.K. and Harris, P.J.C. (2001). Managing Manure to Sustain Smallholder Livelihoods in the East African Highlands. DFID - Natural Resources Systems Programme. HDRA, Coventry, United Kingdom