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Heavy rainfall and flooding in the western part of the state has resulted in lots of questions about nitrogen loss. This is a crucial question that may have serious implications for corn yield and profitability. Back in 2005, we estimated nearly 2 million bushels of lost yield potential in the Holt County Missouri River bottom alone due to N deficiency. This estimate was based on an aerial photo survey and research-based relationships between corn yield and color. This N deficiency was caused by heavy rains over Memorial Day weekend, but no actual flooding of fields. On fields that have gone under water, losses are likely to be even more severe.

For fields that have gone under water but the corn survived well enough to keep the stand, yield response to applying more N now is highly likely. I would say that it is essential to get additional N on these fields.

A general target rate for additional N might be 40-60 lb N/acre in fields that have been submerged. Chances are good that many of them will need more. Which ones? Factors that would lead to greater losses include: sandy texture, well drained, longer submergence, N source was not ammonia, or was ammonia applied in the fall. Consider applying higher rates on fields with more than one of these risk factors.

For fields that were not submerged, but received excessive rainfall, it's likely that additional N would give a yield response, but not as much as fields that have been submerged. The same risk factors apply, except that poor drainage also increases risk of N loss in these fields.

Peter Scharf
University of Missouri
ScharfP@missouri.edu