Rice Hull Ash as Substrate Amendment

Nursery production of woody ornamentals uses pine bark in various sizes as the main component of potting substrate. Pine bark has a low water holding capacity in the beginning of production, which is coupled with a young plant that does not utilize a lot of nutrients, resulting in high leaching and low fertilizer and water use efficiency. Several amendments such as peat moss can increase water holding capacity but will decompose overtime and may result in poor drainage during rainy season or major storms. Rice hull ash (RHA) is a byproduct from power plants and available to Louisiana growers at a low price. It has the potential to increase water holding capacity and less likely to decompose within 6- to 12-month production cycles. In our first experiment, RHA was mixed into pine bark at 0, 5%, 10%, and 20% (by volume) to determine its water holding capacity and leachate chemical properties. In the 2^nd experiment, growth and quality of Knock Out rose ‘Double Red’ in response to RHA at above rates were evaluated for six months. Results indicated that RHA stayed in the 5-gallon container and increased water holding capacity of a grower’s pine bark mix by 16% or 18% at 10% mixing rate when overhead or drip irrigation were used, respectively. ‘Double Red’ Knock Out roses grew larger with greater biomass in the 10% and 20% RHA treatments possibly due to the additional nutrients provided by RHA. However, pH and EC in leachates of 20% rate were significantly higher than the ranges commonly considered safe for many plant species. These results suggest that RHA has the potential to be used as a potting substrate amendment to increase water holding capacity of pine bark but is limited to grow plants that can tolerate high pH and EC, and further study is needed to determine total leachate of nutrients over a longer production cycle before RHA can be recommended for being used in container production.