High rates of gasified rice hull biochar affect geranium and tomato growth in a soilless substrate

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ABSTRACTGasified rice hull biochar (GRHB) is a by-product of rice production, where rice hulls are gasified to generate energy for other aspects of rice processing.Other research studies have shown that GRHB up to 10% (v/v) in a soilless substrate can provide much, but not all, of a potted floriculture crops' phosphorus and potassium needs. The objective of this research was to determine the effect of higher GRHB rates on floriculture crop nutrition and growth. Two experiments were conducted with GRHB rates ranging from 0 to 30% (v/v) of a soilless peat moss-based substrate. Geranium (Pelargonium × hortorum “Maverick Red”) and tomato (Solanum lycopersicum “Megabite”) were grown in 10-cm diameter pots with amended substrates. Addition of GRHB up to 30% affected the physical properties of the peat moss-based substrate by increasing container capacity (CC) and decreasing unavailable water (UAW). Summarizing across the two experiments, amending a peat moss substrate with 15–20% GRHB provided sufficient phosphorus (P) and potassium (K) for production of geranium and tomato in soilless substrates over a 5- to 6-week production cycle. However, GRHB did not provide a sufficient source of micronutrients to support crop growth. Geranium responded negatively to high rates (>10%) with reduced shoot and root growth, while tomato responded positively to higher rates with increased shoot growth. Higher rates of GRHB (>10%) can be recommended for some crops, but not all.