Rice hull-based substrates amended with anaerobic digested residues for tomato transplant production

Some agricultural by-products may be suitable as peat alternatives in root substrates, such as rice hulls, or as fertilizers, such as the anaerobically digested residues of fruit and wine distilleries (ADR). In this study four substrates were prepared with increasing rates (0, 33, 67 and 100%) of ground rice hulls (GRH) as substitution for peat. These mixes were amended, or not, with 20% of ADR. Substrates were physically and chemically analyzed and used to grow tomato 'Jack' seedlings under three irrigation regimes (IR). Water distribution per tray was 225, or 450 ml per day, or 900 ml every 2 days. Total pore space (TPS) was highest in 0% GRH substrates while air-filled porosity (AFP) was highest in 100% GRH. Water holding capacity and easily available water decreased with the increase of GRH and differences between substrates were increased by ADR. ADR reduced TPS and AFP, but not in all mixes. Electrical conductivity was higher when ADR was added. Higher nutrient concentrations were observed in substrates containing ADR. In the cultivation trial, plant height, leaf number and area, and biomass fresh and dry weight were negatively affected by increasing GRH rates, while fertilization with ADR improved plant growth. Among the IR, 450 ml d-1 guaranteed better biomass performances than the other treatments.