Humic acid can increase potato yields, quality, and value

Elmore County Extension Educator Mir Seyedbagheri had long thought that American agriculture—as productive as it was—was “missing something.”

“We had forgotten that soil was a living system and we weren’t adding organic matter,”he says.Since 1987, Seyedbagheri has been investigating the role of humic acid—one of three components of soil humus—on potato yields and quality. Humic acid is rich in carbons, which fuel the activities of beneficial soil microorganisms.

Seyedbagheri’s findings: While most commercial brands of humic acid he tested had no noticeable effects, three did.“But compost or a green manure crop will also make humic acid for you in the long term,”he says.

Recently, Jeff Stark, research agronomist, and Bryan Hopkins, UI Extension potato cropping systems specialist,began evaluating humic acid. In a three-year study at Aberdeen, they determined that applying humic acid and liquid phosphorus in a concentrated band at potato hilling boosts yield and quality compared with applying phosphorus alone.Per acre,overall yields of Russet Burbank potatoes increased by an average 18 cwt, U.S.No.1 yields by 22 cwt, and gross returns by $152. Since the humic acid added just $10 to $20 to production costs,Hopkins agrees that the practice “shows potential as a profitable management tool,”particularly in southern Idaho’s low organic-matter soils.“It seems to make phosphorus more available to plants and allows root growth to proliferate.”

Hopkins cautions potato growers who want to apply humic acid as a soil amendment to work with reputable companies that provide a consistent material and can supply unbiased data showing that their product works under local conditions.

Contact bhopkins@uidaho.edu or mirs@uidaho.edu.

© 2004 University of Idaho, College of Agricultural and Life Sciences.