Comments about flooding Louisiana rice for frost protection

The following is a memo from Johnny Saichuk, Louisiana Extension Rice Specialist, regarding possible injury to rice from cold weather and considerations about protecting rice with a flood. Questions have been raised due to weekend weather forecasts calling for below-freezing temperatures across parts of the South.

Rice at greatest risk is rice that has been planted a few days and is just coming up or just germinating. If rice at this stage is shut down for any length of time, recovery will be difficult, plus it will open the door to seedling disease and insects like the seed midge.

Rice that is at the one leaf or greater stage of growth will likely suffer as much injury from desiccation due to the north wind as it will to cold temperatures.

The only solution I can suggest to reduce the likelihood of injury in either situation is to put a water blanket on the field. In some cases this will not be possible because the ideal situation is to establish a very shallow flood, hold it until Monday then let it go. The time lag to do both is a problem. Furthermore, not everyone agrees that this is the best practice. It is definitely a judgment call. Next week or the week after we will know what we should have done.

The principle is to provide a thermal flywheel. We want the water to warm up and stabilize the temperature during the night. Clear water, while cold initially, will actually warm up very quickly because of the greenhouse effect. It will also allow light to penetrate to the seedlings helping them carry on photosynthesis to a limited degree. Muddy water, while warmer on introduction, prevents photosynthesis (which is why it is better for weed control) and does not benefit as much from the greenhouse effect.

If rice has been drilled into dry soil – too dry to promote germination – I recommend doing nothing. Let the seed sit there until it is warmer then flush if we do not get the predicted rainfall. It should be the rice at least risk.

It will be a tough balancing act to add water to newly planted, partially germinated or just emerging rice to provide some thermal barrier without also causing seedling injury from deprivation of oxygen and light.

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