With Some Exceptions, Blueberries Showing Limited Response to Humic Acids

A three-year trial into the effects of humic acids on Duke and Liberty cultivars is showing that humic acid applications may be beneficial for cultivars with soil sensitivities or in situations where soil needs improving.

But, according to Scott Lukas, Endowed Professor for Northwest Berry Production and Management at OSU, in a well-managed system with good soil conditions, there may be no benefit to adding humic acids to your system.

With one exception, the latest research into whether humic acids can benefit blueberries is showing similar results to past work, which has shown no effect on vegetative growth or yield, despite some positive benefit on root growth in the northern highbush cultivars Draper and Bluecrop.

The latest research, running from 2020 through 2023, again has shown no significant effect on yield in the Liberty cultivar, Lukas said.

“But when we look at the percent change in yield from 2020 to 2022, we do see an impact of humic acid on the treatments with Duke planted on flatbeds,” he said.

While yields increased 22 percent over the three-year period even in areas without humic acids, the increase yields in Duke were 56 percent higher in the humic acid treated plots than in the plots with no humic acid treatments.

“So, that primary response of Duke grown under the lower performing treatment shows that the poorer treatment performed most favorably with the humic acids,” Lukas said.

The experiment included seven applications of a humic acid substance that, according to its label, contained 8.5 percent humic acids and 1 percent potassium. Researchers applied the product at the manufacturer’s recommended rate of 1 gallon per acre per application applied every two weeks from May to July.

“At that rate, you could expect the cost to be somewhere in the ballpark of 38 to 52 dollars per acre,” Lucas said, depending on whether paying bulk rate or piece rate.

Researchers applied the treatment through a drip irrigation system.

Among initial findings, Lukas reported in a presentation at the Oregon Blueberry Field Day July 26 in Aurora, that the humic acid applications had no effect on soil nutrients, on soil pH or on soil organic matter. “And similar to soil nutrients, in the leaves and fruit we did not see any overall effect,” he said.

Researchers are now planning to assess fruit-quality metrics of the different treatments, including firmness, brix, titratable acidity, and also to measure soil biological activity. “And we’re hoping to assess soil water holding capacity in select treatments,” Lukas said.

“There are other impacts that we will be summarizing after we get the final season of data,” Lukas added.