THE TRANSFORMATION OF COMPOSTED ORGANIC RESIDUES INTO EFFECTIVE GROWING MEDIA

Composts made from green wastes cannot usually be used successfully as growing media because they contain levels of water-soluble nutrient salts which are so high as to inhibit plant growth.
In addition, levels of water-soluble nitrogen (N) and phosphorus (P) are usually too low in relation to water-soluble potassium (K) and pH is usually too high.

A process has been developed which converts composts into highly effective growing media by application of phosphoric acid (to add P and reduce pH) and ammonium nitrate (to add N), followed by dilution using a low-nutrient substrate such as coir.
Precise treatment must be tailored individually according to the chemical analysis of the compost and the intended end use.

During 1994–1996, a major composting research project, originally funded by the Department of the Environment and completed by the Environment Agency for England and Wales, has taken compost samples from three different green waste composting operations and transformed them into successful growing media by application of 1.7 to 3.0g ammonium nitrate and 50 ml phosphoric acid (5.4% m/m P₂O₅) per litre of compost, followed by dilution with coir in a ratio of between 1 and 5 parts by volume to 1 part by volume of compost.

Antirrhinum (direct-sown and pricked-out), Stock (direct-sown) and Tomato (pricked-out) all showed significantly enhanced growth where the treatment was applied to compost.
In some cases, untreated compost killed seedlings.
In many cases, treated compost performed as well as with well-established growing media

International Symposium on Composting & Use of Composted Material in Horticulture

A. Rainbow, N. Wilson

Green waste, pH, phosphoric acid, Antirrhinum, Stock, Tomato

https://doi.org/10.17660/ActaHortic.1998.469.7