Effect of biochar on nutrient release and retention in container crops
Basiri, N., F. R. Walker, A. Fulcher, and J. Altland.  2016.  Proceedings of Southern Nursery Association Research Conference, 61:174-180.

Abstract:
Greenhouse and nursery producers are facing increasing fertilizer costs and low nutrient use efficiency. Water management strategies should be based on economic and environmental concerns and modified to increase nutrient uptake efficiency and reduce nutrient losses. Incorporating biochar into nursery substrate can potentially increase soil fertility through its capacity to retain water and nutrients. This research focuses on the impact of switchgrass biochar on nitrate, phosphate and potassium release and retention during 8-week life cycle of Buxus sempervirens ×B. microphylla (‘Green Velvet’ boxwood) and Hydrangea paniculata (Pinky Winky® hardy hydrangea). Pots filled with pine bark and amended with either 10% or 25% (v/v) biochar. Plants were irrigated with a moisture sensor based irrigation when the volumetric water content reach the set point and provided certain amount of water to plants to determine the impact of biochar on water and nutrient leaching. Over the growing season the mass of nitrate and phosphate released was not different in each treatment in hydrangea, whereas potassium release fluctuated more in the biochar amended substrates. In boxwood 25% biochar treatment released higher nitrate and phosphate in leachate over the time while the mass of potassium had greater fluctuations during the growing season. Although the average of leachate analysis over the time showed that higher amount of phosphate and potassium was leached from containers that received 25% biochar, the total amount of water leached and nutrients lost from hydrangea containers were lower in biochar amendment pots in comparison to nonamended pots due to improvements in the water holding capacity of the substrate and fewer irrigation events in the biochar treatments. But the total amount of nutrient lost from boxwood was higher in biochar treatments as there was no differences in the number of irrigation events in boxwood.