Basin Study Finds Dried Sulfur Prills Bring Down Soil pH

Preliminary findings from the first year of a multi-year research project are showing that organic blueberry growers in the Columbia Basin may be able to avoid leaving ground fallow for up to a year prior to planting as they try to bring down soil pH.

The first year’s results are showing that an application of dried sulfur prills at planting, followed by once-a-week applications of micronized sulfur for eight weeks, has the same effect as the current standard practice.

Columbia Basin growers typically apply prilled sulfur at around 1,500 pounds per acre six to twelve months before planting to bring down the Basin’s high pH levels to the 4.5 to 5.5 range that blueberry plants excel at.

“So, it is up to a year that those fields lie fallow,” said OSU graduate research assistant Alexander Gregory at the Oregon Blueberry Field Day in Aurora July 15. “And that is money that these growers are not going to be seeing.”

OSU graduate research assistant Alex Gregory at the Oregon Blueberry Field Day in July said preliminary results from a research project are showing that dried sulfur prills can bring down soil pH.

In the research, launched in 2020 at the Hermiston Agricultural Research and Extension Center, Scott Lukas, the experiment’s lead scientist, and Gregory applied several treatments to eight rows of blueberry plants, including a control that involved applying prilled sulfur eight months pre-plant, and are analyzing the different applications’ effects on soil pH, berry yields, pruning weights, plant height and canopy cover.

“As time goes on, these results will be more robust,” Gregory said, “but we are already seeing some promising treatment effects.”

The most promising to date, he said, is the application of dried prills at planting plus micronized sulfur for eight weeks after planting.

“That has given us pretty much identical results compared to the grower’s control,” he said.

In both treatments, the control and the dried prill, plus micronized sulfur treatment, researchers also applied acidified water with a sulfur burner to help bring down the pH, as well as non-acidified irrigation water in an effort to develop a set of management practices that can control soil pH in organic blueberry plantings east of the Cascades without the use of the sulfur burner.

“So far, we do not have any application that can do away with the sulfur burner,” Gregory said. “We still need to be applying acidified water, or we do see a hit in yield. But that may change over time.”

Gregory characterized efforts to develop an alternative to the sulfur burner, which he described as expensive, hazardous and at risk of being removed from the Organic Materials Review Institute’s list of approved practices, as a major goal of the study.

Researchers also are looking at the dried prills at-plant application and the micronized sulfur application as stand-alone treatments, in addition to testing them in combination with one another.

Gregory told field day participants he didn’t have any definitive answers yet. But, he said, “Preliminary data shows that an application of dried prills with subsequent micronized sulfur injected through the fertigation system can be just as effective as the traditional control of applying prilled sulfur and then waiting six to twelve months.”

One caveat, Gregory noted, is micronized sulfur is listed by OMRI as a foliar fungicide. But, he said, if it is applied through a drip system, it is no longer OMRI listed.

“So, a large part of this project, assuming that these results continue over the coming years, is to petition to add an acceptable use for micronized sulfur, because it is a very promising soil amendment,” Gregory said.