Use of Fresh Rice Hulls and Anaerobic Digestion Residues as Substrates Alternative to Peat

Peat is one of the most commonly used substrates in nursery, vegetable and flower production, mainly because it has good and well known physical, chemical, and hydraulic characteristics. Environmental and technical issues have been arising in the recent years, driving researchers to look for other substrates to both preserve peat bogs and improve physical aspects (e.g. aeration) of this substrate. Ground fresh rice hulls (GRH) have already been used and characterized by several authors and shown to be suitable for producing growing mixes while less is known about the possible use of anaerobic digestion residues (ADR). In this research different combinations of sphagnum peat and GRH (0, 33, 67 and 100% by volume of GRH) with and without ADR (20% by volume), considered as fertilizer, were studied. The mixes were first characterized from a physical and chemical point of view and then tested as substrates for transplant production of tomato and Salvia splendens. The increase of GRH in the mix without residues negatively affected growth of both species, S. splendens in particular. Indeed, when the rate of GRH was higher than 33%, seedlings did not reach marketable size. The addition of ADR improved the characteristics of all mixes so that performances of S. splendens in all substrates were much closer to those of GRH-free substrate.