Nitrogen Fertilization After Flooding

Gordon Johnson, Extension Vegetable & Fruit Specialist;

With heavy rain expected this weekend, flooding can be expected in some vegetable fields. In addition to nitrate leaching, there is potential for significant denitrification losses in saturated soils.

In fields that have been waterlogged for several days, nitrogen fertilization will be critical to helping plants recover.

Root growth and function is impared by flooding and therefore nitrogen uptake will be limited. N levels in soils will be low due to leaching and denitrification. Nitrogen should be applied as soon as soils have drained. Foliar N fertilization may be of great benefit after flooding as root systems recover.

In flooding studies at the University of Florida byYuncong Li, Renuka Rao and Stewart Reed, they tested several N fertilizers both as dry applications and foliar applications for their effectiveness in recovering flood-damaged vegetable crops and found that potassium nitrate performed the best, urea the second best, and calcium nitrate the third best. Liquid urea-ammonium nitrate solutions should perform similarly to urea as a foliar application and as a sidedressing where crops are still small enough to get equipment through. Limit foliar applications to less than 3% total salt solutions. In plasticulture vegetables that have been flooded, foliar applications will be necessary until the beds have dried out enough to allow for fertigation through the drip system.

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