Although corn or soybeans could not be planted on 1.6 million acres of Ohio farmland last year and little to no fertilizer was applied to those fields, the amount of phosphorus entering Lake Erie still was high.
That might seem odd. After all, many of those unplanted acres were in northwest Ohio, the region that feeds into the Maumee River and ultimately into Lake Erie.
But a lot of phosphorus was already present in fields from fertilizer applied years before, and older phosphorus is another contributor to the level of phosphorus in Lake Erie, said Greg LaBarge, an Ohio State University Extension field specialist. OSU Extension is the outreach arm of Ohio State’s College of Food, Agricultural, and Environmental Sciences (CFAES).
Phosphorus runoff from farm fields is a main cause of the harmful algal blooms plaguing the lake.
“Phosphorus was already in fields, ditches, rivers, and tributaries, and it just moved downstream,” LaBarge said.
The rain added momentum. 2019 was the sixth wettest year on record in Ohio, which increased the chances that phosphorus, an ingredient in fertilizers and manure, would travel downstream with the rainwater, said LaBarge, an agronomist involved in a statewide phosphorus water quality monitoring effort.
Given how much rain the state received last year, particularly in northwest Ohio, the predictions for the summer phosphorus levels in Lake Erie were even higher than they turned out to be.
The trend toward more and more rain is expected to continue.
For the state to significantly reduce the phosphorus levels in Lake Erie, a lot more needs to be done besides changing the methods and amounts of fertilizer farmers apply each year to their fields, LaBarge said.