Evaluating Poultry Manure Application Timing and Cover Crops to Maximize Water Quality Benefits in Corn and Soy while Minimizing Cover Crop Yield Drag

Issue

While cover crops are known to reduce nutrient losses like nitrate in drainage water, combining them with manure can sometimes reduce corn yields, especially when manure is applied in the fall. This research aims to understand why that happens and how to avoid it.

Objective

This work will result in best practices for managing poultry litter in systems that use cover crops. The team will also analyze economic trade-offs so farmers can make informed decisions about conservation practices.

Approach

The project uses 27 field plots with individual tile drainage at ISU’s Agricultural Engineering and Agronomy Farm near Boone, Iowa. These plots are used to measure water quality, crop growth, and yield under different combinations of cover crops, fertilizer types, and manure application timing. Researchers are testing whether spring-applied poultry litter, precision placement techniques, or starter fertilizers can improve nitrogen availability for crops in cover-cropped fields while maintaining water quality benefits.

Early results show that while cover crops significantly reduce nitrate losses to water, combining them with fall-applied poultry litter can lead to lower corn yields, possibly because the cover crop uses nitrogen or delays its availability. This study is testing practical solutions already being tried by farmers, like zone-applied manure and using a small amount of starter nitrogen, to overcome such problems. Outreach will include trainings for more than 4,500 manure applicators annually, fact sheets, presentations at field days and expos and updates through blogs and podcasts like The Manure Scoop and Talkin’ Crap. The Iowa Egg Council supports this project and seeks to strengthen water quality and farm profitability across Iowa and the Midwest.