Greg LaBarge, an agronomic systems field specialist at Ohio State University, conducts research on nutrient management and water quality issues. He focuses on the 4R (Right Source, Right Time, Right Rate, Right Place) application management of nitrogen (N), phosphorus (P) and potassium (K) in row crops as well as conservation practices which help limit downstream impacts of nutrients leaving farm fields.
“Having sufficient nitrogen is critical to supporting maximized crop yields, but our studies are showing a significant amount of residual nitrogen in the soil after harvest,” said LaBarge. “Our research has shown that the use of cover crops after corn is an effective way to capture residual nitrogen as organic matter and improve soils.”
He added that identifying and encouraging the deployment of additional practices which keep N in the field is important to achieving both long-term economic and environmental goals.
Greg LaBarge
LaBarge has conducted corn N rate trials for nearly 30 years. The range of N used spanned from zero to 240 lbs. per acre. He wanted to document the amounts of residual N left after corn and started taking total N samples after corn grain harvest.
“In those trials,” he explained, “residual nitrogen from the zero nitrogen plot was consistently around 20 pounds. For the fields that had a 240-pound application, the residual nitrogen ranged from 40 to 200 pounds, depending on the year.”
Last year, LaBarge recorded how his research station data related to farm fields.
“In the fall of 2023, Extension educators and our Water Quality Extension Associate Team in northwest Ohio took fall soil samples from 21 corn fields in Ohio. The average yield was 220 bushels per acre with an average nitrogen rate of 187 pounds applied.”
The average residual N with all fields included in both autumn and spring was 99 lbs./acre. “We went back in the spring of 2024 to measure spring residual nitrogen. The fall average was 156 pounds, but by spring it had dropped to 46 pounds,” he said. He emphasized that most of that N was lost to the environment, unless a cover crop was planted.
He gave some advice to assist corn growers: “Cover crops are tremendous at mitigating field losses of nitrogen. I hope you strongly consider participating in cover crop programs to retain that residual nitrogen on your farm.”
LaBarge also underscored the importance of farmers knowing their soil residual N number. “It is extremely helpful in evaluating your corn nitrogen program if you’ve got a good handle on just where you’re starting,” he said.
by Enrico Villamaino
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