Keratin nursery pots as potential medium for controlled release of copper ions in root growth control in Theobroma cacao, L

Authors: Codling, Eton; Schmidt, Martha; Schmidt, Walter; HUDA, MASUD - Horticultural Research Institute - Washington, Dc

Submitted to: Journal of Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2019
Publication Date: 5/21/2019
Citation: Codling, E.E., Schmidt, M.E., Schmidt, W.F., Huda, M.S. 2019. Keratin nursery pots as potential medium for controlled release of copper ions in root growth control in Theobroma cacao, L. Journal of Horticulture. 6:256.

Interpretive Summary: Horticultural plants like Theobroma cacao L.[the seeds of which are harvested for the products known commercially as chocolate] are grown in nursery pots for research. As the 3-4 feet tall plants in pots typically grow in pots less than 6 inches in height, roots can encircle the inside of the pot adversely affecting plant health and the accuracy and reproducibility of the resesearch results. A commercial product called “SpinOut” containing copper ions when painted on the inside of the pots than releases copper ions which in turn inhibits roots encircling the pot. The present authors had already successfully made nursery pots containing a hybrid between keratin biopolymers synthetic polymers polyethylene (or polypropylene). In this study, the authors incorporated the copper ions into the keratin matrix at three concentrations (1%, 5% and 10%), extruded the hybrid mixture into pellet, and injection molded the pellets in nursery pots. Theobroma plants in the pots for six months; samples from soil, roots, stems and leaves of plants were collected and analyzing for copper. Results demonstrated copper ions leached into the soil until the soil matrix was saturated with Cu+2; above a theshhold soil level of cupric ions, likely due to biophysical and/or biochemical barrier at the roots/soil interface, toxic levels of cupric ions appear to be precluded from entering the plant. The same nursery pot can be used to supply the proper/optimal copper ion concentation for individual plant growth and to control excess plant root growth responsible for root encircling.

Technical Abstract: Copper ions at proper levels are essential for plant cell growth and excess copper ions are toxic to root cell growth. The one meter height Theobroma cacao L. plants have roots in 10-15 cm depth nursery pots. “SpinOut®” high in Cu+2 and painted inside the plastic container mitigates against root encircling. Evidence is presented that a similar physicochemical effect can be obtained by incorporating copper ions into a keratin biopolymer matrix extruded into pellets and injection molded into a pot. Sustained controlled release of Cu+2 is obtained for at least six months. The same technology enables highly uniform delivery of the same amount of micronutrients self-consistently pot to pot. This approach would be useful in urban agriculture in which the biomass formulated composition of a soil matrix is especially non-uniform and in which both the plant and the surrounding soil matrix can be competing from among the same micronutrients.