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Does nitrogen fertilizer application rate to corn affect nitrous oxide emissions from the rotated soybean crop?

Abstract:

Little information exists on the potential for N fertilizer application to corn (Zea mays L.) to affect N<inf>2</inf>O emissions during subsequent unfertilized crops in a rotation. To determine if N fertilizer application to corn affects N<inf>2</inf>O emissions during subsequent crops in rotation, we measured N<inf>2</inf>O emissions for 3 yr (2011-2013) in an Iowa, corn-soybean [Glycine max (L.) Merr.] rotation with three N fertilizer rates applied to corn (0 kg N ha-1, the recommended rate of 135 kg N ha-1, and a high rate of 225 kg N ha-1); soybean received no N fertilizer. We further investigated the potential for a winter cereal rye (Secale cereale L.) cover crop to interact with N fertilizer rate to affect N<inf>2</inf>O emissions from both crops. The cover crop did not consistently affect N<inf>2</inf>O emissions. Across all years and irrespective of cover crop, N fertilizer application above the recommended rate resulted in a 16% increase in mean N<inf>2</inf>O flux rate during the corn phase of the rotation. In 2 of the 3 yr, N fertilizer application to corn (0-225 kg N ha-1) did not affect mean N<inf>2</inf>O flux rates from the subsequent unfertilized soybean crop. However, in 1 yr after a drought, mean N<inf>2</inf>O flux rates from the soybean crops that received 135 and 225 kg N ha-1 N application in the corn year were 35 and 70% higher than those from the soybean crop that received no N application in the corn year. Our results are consistent with previous studies demonstrating that cover crop effects on N<inf>2</inf>O emissions are not easily generalizable. When N fertilizer affects N<inf>2</inf>O emissions during a subsequent unfertilized crop, it will be important to determine if total fertilizer-induced N<inf>2</inf>O emissions are altered or only spread across a greater period of time.