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A study of nitrogen and phosphate fertigation in pear trees shows no differences in yield or fruit quality between trees that are fertigated and trees that received surface applications of dry nitrogen and phosphate fertilizers.

The field experiments, conducted by Oregon State University scientists in a Parkdale pear orchard and at the Mid-Columbia Agricultural Research and Extension Center in Hood River, were initiated in 2005 to learn if switching from surface application methods of banding and broadcasting dry fertilizers to using drip irrigation lines to apply the fertilizer, a method known as fertigation, was effective and economical.

“There was a slight trend toward an increase in yield in the fertigation treatment,” said Dr. Xinhau (Frank) Yin, soil scientist at OSU’s Hood River research station. “But the yield increase was not statistically significant.”

Years ago, pear growers in the region tried to integrate fertigation with their nutrient management program, according to Yin. “But it didn’t work very well.”

He noted that Hood River soils are high in volcanic ash, and phosphate must be carefully managed to ensure adequate levels are supplied to the crop without causing runoff or leaching problems.

Pear trial

He designed a pear trial to see if the uptake of applied phosphate fertilizers could be increased and fruit quality improved, while at the same time reducing the amount of phosphate used. He also wanted to evaluate the effects of nitrogen fertigation and drip irrigation as an integrated production system on fruit yield, quality, and storability of pears as compared to the current system of broadcasting dry fertilizer to the soil surface and using microsprinklers for irrigation.

With only one year of results, Yin is encouraged by the preliminary findings. Though an increase in yield from the fertigation treatment was not statistically different, he found no adverse effects to fruit quality. But the two fertigation treatments in the Parkdale trial, on average, reduced phosphate fertilizer use by 20 percent, compared to the broadcasting treatment.

“Fertigation of phosphate fertilizer under microsprinkler or drip irrigation may be more efficient than surface broadcasting application on the Parkdale soils,” he reported.

In the Hood River trial, water use in the drip irrigation system consumed 73 percent less than the current system of microsprinklers. Differences in fruit size, color, and yield between the fertigation (drip irrigation) and broadcast applications (microsprinkler irrigation) were insignificant.

But major differences were observed in the amount of nitrogen fertilizer used in the two treatments. The fertigation and drip system resulted in 20 percent less nitrogen than the broadcast treatment, he said.

“In summary, our preliminary results suggest that switching to fertigation and drip irrigation do not cause significant reduction in pear productivity, even in the first year,” Yin said.

He believes that the integrated nitrogen and phosphate fertigation and drip irrigation system could be a sound nutrient and water management system for tree fruit production in the region.