Split fertilizer nitrogen application with a cereal rye cover crop reduces tile nitrate loads in a corn–soybean rotation

Splitting fertilizer nitrogen (N) applications and using cover crops are management strategies to reduce nitrate in tile drainage water. We investigated split fertilizer N applications to corn (Zea mays L.) on crop yields and tile nitrate loss in both corn and soybean (Glycine max L.) in rotation from 2016 through 2019. We evaluated the inclusion of cover crops in a split-N treatment. Fertilizer N treatments included 100% in the fall; 50% in the fall + 25% at planting + 25% at side-dress; 100% as spring preplant; 75% as spring preplant (reduced N rate); 50% as spring preplant + 50% at side-dress; and 50% as spring preplant + 50% at side-dress with a cover crop. We did not find significant differences between split and single full rate N application treatments for corn yields or tile nitrate loss; however, the reduced N rate treatment significantly decreased corn yield by 10%. Cumulative tile nitrate losses (over four seasons) ranged from 115 kg ha⁻¹ for all of the N in the fall to 65 kg ha⁻¹ for 50% as spring preplant + 50% at side-dress with a cover crop, a decrease of 43%. Tile nitrate loss responded similarly to (corn) N treatments under both corn and soybean, with 64% of the loss under corn and 36% under soybean. Our results suggest that decreasing the fertilizer N rate may impact corn yield more than nitrate loss, while split fertilizer N application with a cover crop has potential to reduce tile nitrate loss without decreasing crop yield.