Abstract
Economic and environmental concerns limit peat use for substrate production, promoting interest in alternative materials. Hence, in this study, 16 substrates were obtained by mixing, in a factorial combination, eight substrates with different ratios of peat, rice hulls (RH), and anaerobic digestion residues (ADR) and two types of RH: whole (WRH) or ground RH (GRH). Substrates were physically and chemically characterized and then tested as potting substrates for Pelargonium peltatum ‘Ville de Paris’ and Rosa × hybrida ‘La Sevillana’ production. Physical characteristics worsened the increasing RH content. This problem was partly solved using GRH and adding ADR to the substrates. As for chemical characteristics, RH increased P and K, reducing cation exchange capacity, NO3-N, and Ca, thus causing a possible nutritional imbalance. ADR addition increased all nutrients, restoring the nutritional balance. Geranium and rose plants were negatively affected by an increasing rate of RH. In both species, the use of GRH improved the considered parameters, whereas ADR improved some parameters but only in geranium. It was possible to partly substitute peat with 33% RH, but GRH plus ADR is necessary for geranium production, and facultative for rose. The multiple regression method and principal component analysis appear to be useful tools to understand which substrate parameters, and to what extent, influence the growth of ornamental plants.
Highlights
Because of its high porosity, high water-holding capacity, and relatively high cation exchange capacity, peat is the most important ingredient for media production [1]
It was possible to partly substitute peat with 33% rice hulls (RH), but ground RH (GRH) plus anaerobic digestion residues (ADR) is necessary for geranium production, and facultative for rose
Eight other substrates were prepared in a similar manner but using ground RH (GRH)
Summary
Because of its high porosity, high water-holding capacity, and relatively high cation exchange capacity, peat is the most important ingredient for media production [1]. European laws [7] have been passed to limit peat availability, increasing its price [8], especially in southern European countries that import peat. For these reasons, there has been an increasing interest in finding cheap and locally available alternative materials with a sustainable approach [9,10,11]. The alternative materials should have suitable physical and chemical properties, uniform quality, be available in large quantities, and be cost effective [13,14]. Since no universal substrate exists, many materials are mixed with peat to achieve desirable physical and chemical properties [15,16]
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