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Gasified rice hull biochar affects nutrition and growth of horticultural crops in container substrates

Locke, James C., Altland, James E., Ford, Craig W.
Journal of environmental horticulture 2013 v.31 no.4 pp. 195
Helianthus annuus, Pelargonium hortorum, Solanum lycopersicum var. lycopersicum, Sphagnum, Viola wittrockiana, Zinnia violacea, ammonium nitrate, biochar, container-grown plants, containers, fertilizer application, floriculture crops, greenhouse production, horticulture, leaching, mosses and liverworts, nutrient deficiencies, pH, peat, perlite, phosphorus, phosphorus fertilizers, potassium phosphates, prices, rice hulls, soilless media, tomatoes
Phosphate fertilizers used in the production of greenhouse crops can be problematic if released into the environment. Furthermore, the price of phosphate is increasing as demand increases and world supplies decrease. The objective of this research was to determine if gasified rice hull biochar (GRHB), inherently high in phosphorus concentration, could be used as an amendment to greenhouse substrates to eliminate the need for phosphorus fertilizer application. Geranium (Pelargonium xhortorum ‘Maverick Red’), pansy (Viola xwittrockiana ‘Mammoth Blue Deep Dazzle’), sunflower (Helianthus annus ‘Pacino Gold’), zinnia (Zinnia elegans ‘Oklahoma White’), and tomato (Lycopersicon esculentum ‘Mega Bite’) were grown in a standard commercial soilless medium composed of 85 : 15 sphagnum peat moss : perlite (v:v) and amended volumetrically with 0, 5, or 10% GRHB (v/v). A group of plants labeled as NPK-fertilized controls were fertilized with 7.1 mM N, 0.7 mM P, and 1.4 mM K derived from ammonium nitrate (NH4NO3) and potassium phosphate (K2HPO4). Other treatments received 0, 5, or 10% GRHB and fertilized with 7.1 mM N using NH4NO3. Gasified rice hull biochar had little effect on substrate pH over the course of the experiment. While pH was higher with 10% GRHB than NPK30 fertilized controls by 6 weeks after potting (WAP), the difference was only 0.19 pH units. The GRHB used in this study is an excellent source of readily available phosphate when incorporated at 5% or 10%. However, P is readily leached from containers and lacking in substrate solution concentration by 4 WAP when containers are irrigated and leached in a manner similar to this experiment. While the five crops grown in this study were of similar size and lacked any signs of nutrient deficiency when amended with GRHB, foliar concentrations of P were low when their only source was from pre-incorporated GRHB. Gasified rice hull biochar has potential to be used as a 36 P source in floriculture crop production, however, leaching of the substrate must be minimized to prevent P loss.