Water retention characteristics of substrates containing biochar and compost as peat and perlite replacements for ornamental plant production

In Italy peat and perlite are commonly used as growth substrates in ornamental plant nurseries. Requests for ecologically sustainable growth substrates have recently focused research on the study of new media. In this context, biochar and compost, by-products of other production chains, may play a relevant role. Four growth substrates were prepared by mixing (v/v) different porous matrices including a 2-mm sieved sandy loam soil namely: 50% peat and 50% perlite (PPr), 50% compost and 50% biochar (CB), 25% peat, 25% perlite, 25% compost and 25% biochar (PPrCB) and 25% peat, 25% compost and 50% mineral soil (PCM). Water retention curves of porous matrices and growth substrates were determined by standard techniques and the unimodal and bimodal van Genuchten models were fitted to experimental data. The three growth substrates obtained by mixing by-products (CB, PPrCB and PCM) were tested for Lantana camara L. production in a three-months trial performed on 3 L pot plants. The highest plant available water content (PAWC) was obtained for biochar (PAWC = 0.28 cm3 cm-3), while the highest saturated volumetric water content (θs) was obtained for peat (θs = 0.67 cm3 cm-3). Perlite and biochar water retention curves showed a steep decrease in volumetric water content when desaturated probably due to the high macroporosity of the media. The PPr showed higher water retention performances than CB growth substrate. Despite the differences in water retention characteristics, Lantana camara above ground and total plant dry weight were not affected by the growth substrates.