Rain and its Impact on Crop Fertility

We have received rain in great amounts over the past few weeks. This morning, my rain gauge is full, and it’s still raining. Many fields have received over 10 inches of rainfall over the past few days.

One question I have received is:

What is this rain going to do with our fertilizer?

The nutrient of greatest concern should be Nitrogen.  This is because of denitrification and the water solubility of Nitrogen.

“Gaseous loss of nitrogen takes place by denitrification or ammonia volatilization. Denitrification is a process through which nitrate nitrogen (NO3-N) is converted to gaseous nitrogen oxide (N2O) or elemental nitrogen (N2). This involved the action of anaerobic bacteria (those which do not require free oxygen) and commonly occurs in wet or water-logged soils.

Since this is an anaerobic process, gaseous losses from a normal (aerobic) soil are small. However, when soils stay very wet or saturated for long periods, a large portion of the nitrate can be lost.”  From: “What Happens to Nitrogen in Soils?” LINK

Nitrogen loss due to its water solubility is primarily due to runoff.  If the nitrogen is at (or near) the soil surface, this nitrogen can be lost in runoff or soil erosion. Leaching can be a concern in sandy soils, but we have less leaching in heavy clay soils.

So the next question is “what can we do about it?

This is where the opinions differ. I suggest soil testing to 18″ when the field dries. This is the best way to know what nutrients are available in the field. The nutrient requirement of the crop are relatively low prior to bloom so we have some time after the field dries to correct nutrient problems.

The best way to add nitrogen will be adding it to the soil. This should not be done to wet soil because high nitrogen losses will occur. Knife the nitrogen in prior to 1/3 grown square if possible. Later applications could cause root pruning which may cause more harm than good.

Foliar feeding is a controversial topic in cotton production. Soil fertility expert’s opinions differ as to whether foliar feeding is profitable to the crop.

If you choose to apply foliar fertilizer, keep in mind the crop can not uptake more than about 5 lbs N per acre in a single application. To have a benefit, you will need to add foliar feed in multiple applications with your herbicides or insecticides. Leaf injury (salt burn) can reduce the benefit of foliar feeding.

Foliar feed should be tank mixed with an application you are already making.  Making an application solely for the purpose of spraying foliar feed will not likely be profitable.



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