Organic Manures as Sources of Fertiliser Sulphur

Keywords: Animal manure, Organic manure, Plant-availability, Slurry, Sulphate, Sulphur.

On a global scale, sulphur (S) excretion from domestic animals may be estimated to around 8 million tonnes per year, corresponding to 80% of the World sulphur consumption for mineral fertiliser manufacture. The utilisation of this potential source of fertiliser-sulphur is discussed focusing on the use of manure from housing and manure storages applied to agricultural land. Especially in the developed countries the sulphur content of manure collected from cattle and pigs (1 million tonnes sulphur per year) has a potential as sulphur-fertiliser, as legal demands on the utilisation of manure nitrogen (N) and/or phosphorus (P) already require the use of animal wastes as fertilisers. Content and composition of manure-sulphur from both monogastrics and ruminants may be extremely variable, depending on the sulphur content of the feed. If the diet has a sulphur content balanced according to the animal requirement then the sulphur content of the manure will be relatively low and the main part of sulphur 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 sulphate into organic sulphur and gaseous compounds that may be lost by volatilisation. In this situation the plant-availability in the year of application may be too low to be taken into account in fertiliser practice. A residual long-term effect of the organic sulphur fraction must be expected. The ability of a cropping system to use mineralised sulphur depends on the length of the growing season of the crops, but mineralisation is unlikely to fully meet the sulphur-demand of a crop. There is a need for quantitative investigations of the relations between dietary sulphur 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.