Keywords: Animal manure, Organic manure, Plant-availability, Slurry, Sulfate, Sulfur.

On a global scale, sulfur (S) excretion from domestic animals may be estimated to around 8 million tonnes per year, corresponding to 80% of the World sulfur consumption for mineral fertilizer manufacture. The utilisation of this potential source of fertilizer-sulfur is discussed focusing on the use of manure from housing and manure storages applied to agricultural land. Especially in the developed countries the sulfur content of manure collected from cattle and pigs (1 million tonnes sulfur per year) has a potential as sulfur-fertilizer, as legal demands on the utilisation of manure nitrogen (N) and/or phosphorus (P) already require the use of animal wastes as fertilizers. Content and composition of manure-sulfur from both monogastrics and ruminants may be extremely variable, depending on the sulfur content of the feed. If the diet has an sulfur content balanced according to the animal requirement then the sulfur content of the manure will be relatively low and the main part of sulfur is expected to be in organic forms not available to plants. If the manure is stored under anaerobic conditions over a time span of months there is considerable risk of microbial transformations of sulfate into organic sulfur and gaseous compounds that may be lost by volatilization. In this situation the plant-availability in the year of application may be too low to be taken into account in fertilizer practice. A residual long-term effect of the organic sulfur fraction must be expected. The ability of a cropping system to use mineralised sulfur depends on the length of the growing season of the crops, but mineralization is unlikely to fully meet the sulfur-demand of a crop. There is a need for quantitative investigations of the relations between dietary sulfur input, loss during storage and plant utilisation in the field.

Jørgen Eriksen, Danish Institute of Agricultural Sciences, PO Box 50, 8830 Tjele, Denmark.

20 pages, 7 figures, 2 tables, 42 references.