Suitability of two types of organic wastes for the growth of sclerophyllous shrubs on limestone debris: A mesocosm trial

This study investigated whether overlaying organic wastes directly on limestone debris allowed the growthof sclerophyllous shrubs; the aim was to explore the feasibility of rehabilitation of sites destroyed byquarrying activity. In an open air mesocosm experiment two types of organic material were compared:compost from municipal wastes (C) and a mixture of compost and poultry manure added with wheat husk(C-PW). Mesocosms were pots (1 m diameter, 60 cm height) containing limestone debris covered by theorganic material. Seven mesocosms with C and seven mesocosms with C-PW were planted withsclerophyllous shrubs (Laurus nobilis L., Phillyrea angustifolia L. and Quercus ilex L.). The substrates werecharacterised in terms of chemical and physical parameters, microbial activity and biomass, and total andactive fungal biomass. Shrub photosynthetic performance and growth were evaluated. Over the wholeexperimental period, organic matter mineralization was higher in C-PW. Microbial biomass and respirationwere higher in C-PW than in C but after one year no statistically significant difference between the twosubstrates occurred. Fungal mycelium was a minor fraction of the microbial community in both types ofsubstrates and decreased dramatically after setting up the mesocosms. The metabolic quotient was higher inC suggesting more stressful conditions as compared to C-PW. Both substrates allowed shrub growth;however photosynthetic rates and the increase of plant size were higher on C-PW than on C. The resultsdemonstrated that, as compared to only compost, the mixture of compost and poultry manure added withwheat husk is a substrate more suitable to both microbial processes and plant growth. Therefore a plan torevegetate quarries based on the use of organic wastes as a substrate for sclerophyllous shrubs could befeasible and, what is more, helpful to mitigate the environmental impact of organic wastes disposal.