What is in this article?:
- Crop nutrients analysis/management in post-flood conditions.
- Tips on nitrogen offered.
How much lost N?
The answer to this question will vary among, and within, individual fields and depends on many factors. The factor that may have the single greatest influence is when nitrogen fertilizer was applied.
The situations outlined below will not fit all fields, but should provide a general assessment that can be used to estimate nitrogen losses and develop a management plan.
Preplant nitrogen: Most of the corn in Arkansas was planted at least three or more weeks ago and received some amount of preplant nitrogen. Assuming that most preplant nitrogen is applied as urea, the majority of the nitrogen had been converted to nitrate by the time the heavy rains began.
Nitrate is susceptible to leaching on well-drained soils (sandy) or denitrification (loss as nitrogen gas) on poorly-drained soils. The amount of rainfall and how wet the soil is will dictate the fate of the nitrogen.
In fields that received high amounts of rainfall, but did not have standing water, a large proportion of the nitrate may have been leached or moved laterally with runoff. On fields that were saturated or had standing water, general estimates are that up to 5 percent of the soil nitrate will be lost for each day the soil is saturated or flooded.
Side-dressed nitrogen: Several growers had corn that was approaching the V6 or V7 stage and had applied their side-dress N to relatively dry soils in the days before the heavy rain started. This situation has some similarities to how preflood urea-N is managed for rice.
When urea was applied, 80 percent to 90 percent of the nitrogen is likely still in the field and plant available, regardless of how much rain occurred or whether the field was saturated.
For fields receiving UAN, nitrogen loss is expected to be greater. This is because about 25 percent of fertilizer nitrogen in UAN is in the nitrate form (60 percent to 65 percent of applied is available).