POSSIBILITIES OF SEWAGE SLUDGE USED AS A FERTILIZER IN AGRICULTURE

Sewage sludge has many advantages – firstly the content of organic matter which can improve the soil structure and secondly the presence of nutrients as N, P, K. In this way sludge can be a substitute for the expensive inorganic fertilizers.
Hence the use for agricultural purposes is limited by the presence of pathogens and by the content of heavy metals, which may cause serious problems when the sludge is applied to crops grown for animal or human consumption.

Composting the sludge stands for a possible amelioration of the quality resulting in a stabilisation and in a reduction of the number of pathogens.

Experiments were carried out to test the usefulness of sewage sludge and composted sewage sludge both to enrich poor soils and as a potential growing substrate.
In view of using sewage sludge in horticulture (vegetables), on ornamentals or on public green, its influence was tested on lettuce (Lactuca sativa) on Cordyline terminalis and on a mixture of grasses.

It was our intention to find out relations between the chemical analysis data of the sewage sludge and the biological evaluation by growth experiments on the test plants as named above.

The effect of heavy metals present in the sewage sludge is not the primary reason for production increase or decrease.
An unbalanced supply of N, P, K, Ca²⁺, Mg²⁺ or C1^– seems to have a stronger effect.
Besides the positive influence as a possible substitute for inorganic fertilizers, the concentration of heavy metals needs greater caution.
They will not only result in a contamination of the food chain but also of soil and ground water.
In this way sewage sludge may cause even problems in the public green.

International Symposium on Substrates in Horticulture other than Soils In Situ

J. Coosemans, C. Van Assche

https://doi.org/10.17660/ActaHortic.1984.150.52