Gasified rice hull biochar affects nutrition and growth of five horticulture crops in container culture

Authors: Locke, James; Altland, James; Ford, Craig

Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2013
Publication Date: 12/1/2013
Citation: Locke, J.C., Altland, J.E., Ford, C.W. 2013. Gasified rice hull biochar affects nutrition and growth of five horticulture crops in container culture. Journal of Environmental Horticulture. 31(4):195-202.

Interpretive Summary: Intensive production of ornamental crops in confined areas is recognized as a potential contributor to environmental nutrient pollution, especially with highly soluble nutrients such as phosphorus. In addition, the world-wide supply of phosphate is limited and with increasing demand for fertilizer to meet increasing crop production needs, the price of fertilizer will rise. The goal of this research project was to determine if an alternative source of phosphorus-rich material (biochar) could be utilized in the production of greenhouse crops and to evaluate if phosphorus could be conserved within the growing system. Biochar, the end product of biomass conversion, is reported to have the ability to absorb and retain nutrients, making them available to plants over an extended time period. We chose to evaluate a biochar produced by complete gasification of rice hulls which are known to be high in phosphorus content. We incorporated minimal amounts of the biochar into a commercial soilless growing medium composed of sphagnum peat moss and perlite (85:15) which is inherently low in nutrients and then evaluated the growth of five diverse horticultural crops (geranium, pansy, sunflower, zinnia, and tomato). The crops were compared to plants grown with a regular soluble fertilization program for both visual growth and nutrient analysis of the tissues. Sufficient phosphorus was shown to be available in the biochar-amended media to support growth equal to the ones grown under the regular fertilizer program. However, the phosphorus in the growing medium was depleted after about four weeks to a point that then resulted in a phosphorus deficiency in the plant tissues. The conclusion of the research is that although biochar could supply sufficient phosphorus to adequately support early growth of these crops, either supplemental phosphorus needed to be added beginning at about the four week point or some cultural procedure would have to be employed to prevent leaching of soluble phosphorus from the growing medium.

Technical Abstract: 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.