Dolomite and micronutrient fertilizer affect phosphorus fate when growing crape myrtle in pine bark

Authors: Shreckhise, Jacob - Jake; Owen Jr, James - Jim; EICK, MATTHEW - Virginia Polytechnic Institution & State University; NIEMIERA, ALEXANDER - Virginia Polytechnic Institution & State University; Altland, James; JACKSON, BRIAN - North Carolina State University

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2020
Publication Date: 5/7/2020
Citation: Shreckhise, J.H., Owen Jr, J.S., Eick, M.J., Niemiera, A.X., Altland, J.E., Jackson, B.E. 2020. Dolomite and micronutrient fertilizer affect phosphorus fate when growing crape myrtle in pine bark. HortScience. 55(6)832-840. https://doi.org/10.21273/hortsci14558-20.
DOI: https://doi.org/10.21273/hortsci14558-20

Interpretive Summary: The potting media used to grow nursery plants in containers are commonly amended with dolomitic limestone (DL) and micronutrient fertilizer (MF) to improve fertility. Past research has shown that some of the components of these amendments (e.g., calcium, iron, manganese, magnesium) can interact with phosphorus (P), reducing its solubility and, potentially, plant availability. The objective of this research was to determine the effect of DL and MF amendments on total P (TP), total dissolved P (TDP), and orthophosphate-P (OP) concentrations in pour-through extracts and their relative influence on P uptake by container-grown crape myrtle. Containerized crape myrtle were grown for three months in a pine bark growing medium with no amendments (control), DL, MF, or DL+MF. Water extracts were taken from the growing medium weekly and analyzed for nutrient concentrations. After three months, plants were harvested for measurement of plant dry weight and tissue nutrient content. We found that adding DL+MF to the growing medium reduced OP and TP concentrations in extracts by over 55%. The DL amendment treatment resulted in highest OP (plant-available form) concentrations in water extracts, and this was attributed partially to lower P uptake by plants grown in the DL-only pine bark. Phosphorus content in plant tissue was no different between the control and DL+MF treatments, suggesting that the relatively low concentrations of soluble P in the DL+MF potting mix did not hinder plant uptake of P. This research indicates that adding DL+MF to pine bark-based growing media may reduce the amount of P susceptible to leaching from containers without negatively impacting plant growth and P uptake.

Technical Abstract: Soilless substrates are amended with dolomite and sulfate-based micronutrients routinely to improve fertility, but the effect of these amendments on phosphorous (P) in substrate pore-water during containerized crop production is poorly understood. The objectives of this research were to 1) compare the effects of dolomite and sulfate-based micronutrient amendments on total P (TP), total dissolved P (TDP), orthophosphate-P (OP), and particulate P (PP; TP - TDP) concentrations in pour-through extracts; 2) model saturated solid phases in substrate pore-water using Visual MINTEQ; and 3) assess the effect of dolomite and micronutrient amendments on growth and subsequent P uptake efficiency (PUE) of Lagerstroemia ‘Natchez’ (crape myrtle) potted in pine bark. Containerized crape myrtle were grown in a greenhouse for 91 d in a pine bark substrate containing a polymer-coated 19N–2.6P–10.8K controlled-release fertilizer (CRF) with one of four substrate amendment treatments: no dolomite or micronutrients (control), 2.97 kg·m-3 dolomite (FL), 0.89 kg·m-3 micronutrients (FM), or both dolomite and micronutrients (FLM). Pour-through extracts were collected approximately weekly and fractioned to measure pore-water TP, TDP, and OP and calculate PP. Particulate P concentrations in pour-through extracts were generally unaffected by amendments. Relative to the control, amending pine bark with FLM reduced water-extractable OP, TDP, and TP concentrations by ˜56%, had no effect on P uptake efficiency, and resulted in 34% higher total dry weight (TDW) of crape myrtle. The FM substrate had a similar effect on plant TDW and PUE as FLM and reduced pore-water OP, TDP, and TP concentrations by 32% to 36%, compared to the control. Crape myrtle grown in the FL substrate had 28% lower TDW but similar pour-through OP, TDP, and TP concentrations as the control. Chemical conditions in FLM were favorable for precipitation of manganese hydrogen phosphate (MnHPO4) which may have contributed to lower water-extractable P concentrations in this treatment. This research suggests that amending pine bark substrate with dolomite and a sulfate-based micronutrient fertilizer should be considered as a best management practice for nursery crop production.