New growing media and value added organic waste processing

Public pressure to use peat alternatives in horticultural rooting media offers room for the re-use of local organic waste materials. The re-use of organic wastes requires value added processing such as composting, co-composting, digestion, fractioning/sieving, pressing, binding, stabilising by torrefaction and charification, washing and nutrient exchange. Three cases are presented. In case 1, the new growing media project showed a successful reduction of peat in potting soil mixes at nurseries of 15 plant species. Peat use decreased from 78 to 27%-v/v. The 51%-v/v extra peat alternatives used were, averaged over all mixes used, 24%-v/v coir products, 13%-v/v wood fibre, 6%-v/v bark products and 2%-v/v for each of compost, rice husks, perlite or rockwool granulate. When compared to the standard control mixes yield decreased for two species, increased for two species and was equal for the remaining species. Important, sometimes limiting, properties were stability, nitrogen fixation, EC level, sodium level, rewetting rate and water holding capacity. In case 2 torrefaction at 250°C was used to turn a fast degrading nitrate fixing reed (Phragmites australis) into a non-toxic potting soil constituent which could be added to potting soil mixes up to 80%-v/v. In case 3 the cation exchange complex of coir was measured and saturated with calcium ions. The amount and concentration of a solution necessary to exchange sodium and potassium was 600 meq kg-1 and was dosed as 10 L of 30 mmol L-1 calcium nitrate. In all 3 cases product quality measurements and adapted processing or cultivation practises were discussed. A set of the most important measurements is presented, including: pH, EC, EC level, sodium level, potassium level, stability, nitrogen fixation, easily available water and rewetting rate. In conclusion additional or adapted processing of organic waste guided by proper measurements can increase the value of such organic waste for use in horticulture.