Understanding complexity in the response of ornamental rosemary to different substrates: A multivariate analysis.

Alternative substrates for peat replacement are requested for growing potted ornamental plants in horticulture. A multivariate exploratory data analysis was proposed here with the aim to understand the complexity of plant response to different substrates. Twenty-four substrates were tested by mixing increasing doses (30, 50, 70%, v/v) of eight different composts, instead of peat, with a fixed inert material (30%, v/v). The eight composts were obtained by composting different residual organic materials (mixed compost) or a single material (green compost): (C1) green pruning wastes (70%) + urban sludge (30%); (C2) grape stalk (70%) + urban sludge (30%); (C3) olive mill wastes; (C4) differentiated collection of organic wastes (DOW); (C5) green pruning wastes; (C6) dairy industry wastes (50%) + green pruning wastes (50%); (C7) DOW (35%) + urban mud (30%) + green pruning wastes (35%); (C8) DOW (35%) + urban mud (30%) + grape stalk (35%). The effect of selected physical and chemical characteristics of prepared substrates (55 variables) on ornamental rosemary cultivation has been evaluated by principal components analysis (PCA), hierarchical cluster analysis (CA) and a non-hierarchical CA (k-means clustering). Results indicate that the proposed composts can be used as growing media but the best peat substitution dose is highly depending on the type of composted organic wastes. Most suitable substrates for rosemary growth contained C1, C5 or C6 composts up to 70% rate, C7 compost at 30% and 50% rates, C2 or C8 compost only at 30%. Multivariate analysis proved to be a relevant tool when evaluating comparatively many substrates and a wide number of variables.