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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Production and Genetic Improvement Research Unit » Research » Research Project #438663

Research Project: Can Humic Acids Improve Production in Mature Organic Northern Highbush Blueberry?

Location: Horticultural Crops Production and Genetic Improvement Research Unit

Project Number: 2072-21000-055-014-G
Project Type: Grant

Start Date: Aug 1, 2020
End Date: Oct 31, 2023

1. Study whether adding OMRI-approved humic acids to a standard fertigation program in organic blueberry production improves plant performance.

A long-term trial was established in October 2006 at OSU-NWREC in Aurora, OR. The site has been certified organic (Oregon Tilth) since the first fruiting season in 2008. For the first 10 years of the study (2006-2016), there were 48 treatments in the trial arranged in a 2 x 4 x 6 split-split plot design with five replicates and including two planting configurations (flat ground and raised beds) as main plots, four fertilizer treatments as subplots (feather meal and fish emulsion, each applied initially at “low” and “high” rates of N), two cultivars (‘Duke’ and ‘Liberty’) and three mulch treatments (sawdust, yard-debris compost + sawdust, and weed mat) as sub-subplots (240 plots). Fertilizer sources were: 1) Feather meal (13N–0P–0K) split in March and April, or 2) fish solubles (4N–0.4P–0.8K) fertigated bi-weekly from April-June. Yield was hand-picked. Plants from 40 plots were dug and analyzed for a related research study, leaving 200 plots remaining. In 2017, a study was conducted on how alternate fertilization programs mitigate nutrient problems found with the treatments used from 2006 to 2016 of the trial. From 2017 to 2019, the study switched to a plant-based nutrient source that could be fertigated (Westbridge Biolink Vegan N 5.5–0–0 or 14–0–0, depending on year, 95 lb N/acre) and all existing mulches were replaced with new weed mat. Changes in soil and plant nutrient status and yield (hand- and machine-picked) were monitored. After three years, differences in soil organic matter (SOM) are still be observed due to previous mulch treatments (highest with compost + sawdust, lowest with weed mat), and those plots with higher SOM have shown greater increases in yield from 2017 to 2019 than those with lower SOM. The impact of fertilizer source and rate has diminished over time, as everything is now fertilized the same. Cultivar is now the greatest impact on leaf and fruit nutrients (soil nutrients have only been studied in ‘Duke’, which is more sensitive to changes in soil conditions than ‘Liberty’). In this study, the entire planting will continue to be fertigated the same. However, half of the field, randomly assigned, will be fertigated with an OMRI-approved humic acid at the manufacturer recommended rate and timing. Treatments will be humic acid (with and without) and cultivar (‘Duke’, ‘Liberty’) with 50 plots per treatment combination. Long-term management, particularly for mulch type have led to considerable variation in SOM, soil nutrient levels, and plant growth. Treatment will analyze effects not just in absolute performance, but also in changes over time. Data will be collected on yield, leaf nutrient concentration, soil nutrient levels, pH, and SOM. Results will be presented in articles, oral presentations and journal papers.