Down to Earth: Research Encourages Savvy Interpretation of Fertilizer Recommendations

By Lael Gilbert

Alongside many of life’s essentials, the cost of fertilizer has jumped significantly in recent years, with some components doubling or tripling in price due to supply chain disruptions and global competition. Fertilizer is one of the most expensive parts of crop production, and that cost comes out of farmer’s pockets and profits.

A key financial question then is: How much fertilizer is enough?

“You’d think that it would be a pretty straightforward question for common crops,” said Matt Yost from Utah State University’s Department of Plant, Soils & Climate. “But it is surprisingly hard to get a straight answer.”

Yost is part of a team that recently published research on the topic.

Fertilizer levels affect not only a farm’s bottom line, but crop yields, water quality and airsheds far beyond the field where they are applied.

Farmers can get fertilizer recommendations based on soil samples they send to be chemically analyzed, including from USU’s Analytical Laboratories and other public and for-profit labs. But these analyses and the resulting recommendations can vary greatly from lab to lab — commercial labs tend to be more liberal, and university and public labs more conservative with nutrients and amounts, according to Megan Baker, lead author on the research and recent PhD graduate from PSC.

To better understand the variability coming out of soil labs, the research team sent soil from 12 different farms in Utah and Wyoming to five different professional laboratories for analysis and fertilizer recommendations — two university labs and three private commercial ones.