Dolomite and micronutrient fertilizer affect phosphorus fate in pine bark substrate used for containerized nursery crop production

Authors: Shreckhise, Jacob - Jake; OWEN, JAMES - Virginia Polytechnic Institution & State University; EICK, MATTHEW - Virginia Polytechnic Institution & State University; NIEMIERA, ALEXANDER - Virginia Polytechnic Institution & State University; Altland, James; WHITE, SARAH - Clemson University

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2019
Publication Date: 9/26/2019
Citation: Shreckhise, J.H., Owen, J.S., Eick, M.J., Niemiera, A.X., Altland, J.E., White, S.A. 2019. Dolomite and micronutrient fertilizer affect phosphorus fate in pine bark substrate used for containerized nursery crop production. Soil Science Society of America Journal. 83(5):1410-1420. https://doi.org/10.2136/sssaj2018.12.0493.
DOI: https://doi.org/10.2136/sssaj2018.12.0493

Interpretive Summary: Phosphorus (P) leaching and subsequent runoff from nursery containers during irrigation may have serious environmental consequences due to the effect P on toxic algal blooms in surface waters. The availability of P to algae depends on the form and species of P in runoff, parameters that are currently unknown of P that leaches from pine bark based potting substrates. Furthermore, dolomite and micronutrient fertilizers, common amendments added to pine bark substrate, could impact P concentration, form, and species in water draining from nursery containers. The objectives of this research were to 1) determine the effect of dolomite and micronutrient fertilizer amendments on P partitioning among four P fractions (i.e., orthophosphate-P [OP], non-orthophosphate dissolved P [NODP], total dissolved P [TDP], and particulate P [PP]) in leachate (i.e., drainage water after irrigation) of pine bark substrate, and 2) model P speciation in pine bark leachate using Visual MINTEQ. This study was conducted in a laboratory, and leachate samples were collected from fallow pine bark columns. Amending pine bark with dolomite and micronutrient fertilizer reduced leachate OP concentrations by 70% when averaged across sampling dates, primarily due to retention of OP in the substrate by dolomite. The NODP fraction was unaffected by amendments, and the TDP fraction was 74% to 86% OP. The predominant P species modeled in leachate were MnHPO4 and Ca5(PO4)3(OH). Results of this study suggest amending pine bark with dolomite and micronutrients is a best management practice for reducing P leaching from containerized nurseries.

Technical Abstract: Dolomite and a micronutrient fertilizer are routinely incorporated into a pine bark-based soilless substrate when producing containerized nursery crops, yet the effect of these amendments on phosphorus (P) is not well understood. The objective of this research was to determine the effect of dolomite and micronutrient fertilizer amendments on P partitioning among four P fractions (i.e., orthophosphate-P [OP], non-orthophosphate dissolved P [NODP], total dissolved P [TDP], and particulate P [PP]) and to model potential P species in leachate of pine bark substrate. Amendment treatments incorporated into bark at experiment initiation included 1) a control (no fertilizer, dolomite, or micronutrient fertilizer), 2) controlled-release fertilizer (CRF), 3) CRF and dolomite, 4) CRF and micronutrient fertilizer, or 5) CRF, dolomite, and micronutrient fertilizer. Phosphorus fractions in leachate of irrigated pine bark columns were determined at eight sampling times over 48-days. Amending pine bark with dolomite and micronutrient fertilizer reduced leachate OP concentrations by 70% when averaged across sampling dates primarily due to retention of OP in the substrate by dolomite. The NODP fraction was unaffected by amendments, and the response of TDP was similar to that of OP. Particulate P was present throughout the study and was strongly correlated particulate Fe and DOC concentrations. Visual MINTEQ indicated MnHPO4 and Ca5(PO4)3(OH) were consistently saturated with respect to their solid phase in treatments containing CRF. Results of this study suggest amending pine bark with dolomite and micronutrients is a best management practice for reducing P leaching from containerized nurseries.