Biochar and green compost as peat alternatives in the cultivation of photinia and olive tree

The use of peat in nursery media has a high environmental impact and the finding of alternative materials is quite advisable. In order to evaluate the possibility of replacing peat with biochar and green compost, a growing trial has been performed using two types of biochar, obtained from residues of olive tree pruning or from olive pomace, respectively. Both the biochar types were mixed in different percentages (0, 10, 20% by vol.) in substrates containing green compost from pruning residues (0, 20, 30, 40, 50% by vol.), blonde peat (0, 20, 30, 40, 50% by vol.) and pumice (50% by vol.). Photinia x fraseri Red Robin and Olea europaea Frantoio, susceptible and resistant species to salinity, respectively, have been used in a trial arranged in a completely randomized block design. For photinia the medium composed by peat and pumice 1:1 by vol. performed better, nevertheless no significant growth reduction with biochar addition was observed. Moreover, photinia benefited from the substitution of peat with biochar in the 30% green compost amended substrate, pointing out that at least a partial peat substitution may be useful. In the other mixture combinations, photinia performed better when no compost was used or when biochar was present with green compost. For olive tree no significant effect on plant height was detected, whereas branching was lightly reduced in the medium containing 30% peat, 20% biochar and 50% pumice. Nevertheless, no treatment was significantly different from the mixture with 50% peat and 50% pumice, which was considered as the control. Olive tree has proved resistant to salinity, and it performed well both with green compost and without it. There was no difference between the two types of biochar.