Based on planting date most of the cotton across the state will be in peak bloom during August. Depending on what week of bloom you are in the water requirements for the crop will range from 1.3 (0.18” per day during week one of bloom), up to 1.5 (0.22” per day during week 3 of bloom). Once the crop moves later into bloom the water requirement begins to drop back off.
We have had an abnormally hot summer, and unfortunately we have not had ample rainfall across most of the state. The rainfall that we have been receiving has been very sporadic and is leaving many of our dryland crops in poor shape. If you are in one of the areas that is not receiving adequate rainfall, depending on the week of bloom your crop is in you may require irrigation every three days.
The hotter days with lower humidity mean that irrigation efficiency is going to be lower than normal, and this should be considered when irrigation is applied and the next event is scheduled. With a water requirement of around 0.25 inches per day, an irrigation event of 0.75 inches would not last three full days when efficiency is accounted for.
The typical efficiency of an overhead center pivot with drops is around 80- 85%, meaning that you are losing about 1/5 of the irrigation you are applying during each event. Thus, it is critical, that the weather, environmental conditions, irrigation timing and amounts all be accounted for when making scheduling decisions.
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Even with this scenario on rainfall, it is very important in the state of Georgia that you do not over-irrigate the crop later in the season, especially when we are receiving rainfall and have high humidity. The additional irrigation in the canopy will cause boll rot issues. Monitor your field closely once you are between the 7th-9th weeks of bloom for signs of open bolls.
Bloom is a critical time to ensure the crop is receiving the required amount of water, however, caution should be used, and it is strongly advised that you closely monitor the amount of rainfall that is received on each of the fields and adjust your irrigation applications accordingly. Let’s make sure that we finish this crop off correctly from the perspective of irrigation management.
All of the water requirements can be found in the cotton production guide irrigation section.