Response of northern highbush blueberry to fertigation and granular applications of phosphorus fertilizers

Authors: LEON-CHANG, DAVID - Oregon State University; Bryla, David; Scagel, Carolyn

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2022
Publication Date: 1/1/2023
Citation: Leon-Chang, D.P., Bryla, D.R., Scagel, C.F. 2023. Response of northern highbush blueberry to fertigation and granular applications of phosphorus fertilizers. Acta Horticulturae. 1357:51-58. https://doi.org/10.17660/ActaHortic.2023.1357.8.
DOI: https://doi.org/10.17660/ActaHortic.2023.1357.8

Interpretive Summary: We previously found that fertigation (application of liquid fertilizers through the irrigation system) with nitrogen produced more growth and higher yields than conventional granular fertilizers in northern highbush blueberry. The objective of the present study was to determine whether fertigating with phosphorus (P) fertilizer is also more effective than traditional methods of P fertilizer application in highbush blueberry. Phosphorus deficiency often occurs in blueberry, and the current recommendation is to apply granular P fertilizers when the plants are deficient. Regardless of how it was applied, P fertilizer had no effect on fruit production or the concentration of P in the leaves of the plants; however, after 2 years, granular P increased the concentration of P in the roots, which reduced root colonization by beneficial soil fungi called mycorrhizae. The soil at the study site was high in clay and likely bound much of the P applied as fertilizer. More research is needed to understand why and to determine whether more P in the plants would be beneficial or detrimental to highbush blueberry.

Technical Abstract: Previous studies indicated that fertigating with N was more effective than using granular N fertilizers in northern highbush blueberry (Vaccinium corymbosum L.). The objective of the present study was to build on these findings and determine whether fertigation was also an effective method for applying P. The trial was located in western Oregon and conducted in a mature planting of ‘Duke’ and ‘Bluecrop’. Treatments were applied for 2 years to both cultivars and included no P, a single application of P fertilizer in the spring (early April) using granular monoammonium phosphate at the highest recommended rate of 30 kg/ha P, and weekly fertigation from mid-April to late-July with liquid ammonium polyphosphate at a total rate of 15 or 30 kg/ha P per year. Each treatment was also fertilized with 224 kg/ha N and 1.5 kg/ha B per year. In the year prior to applying the P treatments, the concentration of P in recently expanded leaves was low in both cultivars (0.08-0.09%) and below the recommended level for blueberry in the region (> 0.10%). Fertigation and granular applications of P fertilizer increased the concentration of P in soil solution within the root zone, but neither had any effect on yield, berry weight, or berry firmness in either cultivar. These treatments also had no effect on leaf P. In fact, the concentration of P in the leaves was no different than it was prior to applying any P to the plants; however, granular P increased the concentration of P in the roots of both cultivars and tended to reduce root colonization by mycorrhizal fungi in ‘Bluecrop’. The soil at the site was high in clay and likely bound much of the applied P. Questions remain on whether blueberry requires less P than recommended or if alternative sources or rates of P fertilizer are needed.