Urban composts as an alternative for peat in forestry nursery growing media

Abstract

Including urban composts in nursery growing media could reduce peat use and promote new markets for these products. The objective of this work was to study the effects of compost incorporation in forestry nursery growing media. Growing media were prepared mixing composts (0-75% in volume) from biosolids, municipal solid waste and pruning waste with peat. As control treatment, a peat-based substrate was employed. Hydrophysical and chemical properties of growing media were determined. Moreover the effects of these growing media on rosemary and cypress plant growth (height, stem diameter, nutrient contents) in propagation and production trials were monitored. Hydrophysical properties of compost based growing media were adequate up to 50% compost. The Carbon/Nitrogen ratio of composts (10.7-12.4) was indicative of compost maturity. Compost EC values frequently surpasses those of standard peat substrates, therefore substrate salinity limited the maximum percentage of compost in substrates. In the case of cutting propagation, rosemary growth was increased to 50% compost (EC 1.1-1.3 dS m-1). Cypress seed germination was not affected until 75% compost (EC 1.4-1.9 dS m-1) and its growth was increased in all compost growing media. Plant growth increased was related to the fertilizing effect of compost. Although composts content of Ni, Zn, and Pb were greater than those of standard peat substrates, only concentration of Zn was greater in compost-media cultivated plants. As a general rule, forestry nursery growing media could incorporate up to 50% composts from biosolids, municipal solid waste and pruning wastes mixed with peat.