Sidedressing is Underway in Cotton

Farmers are just wrapping up the Cotton planting season for the 2017 crop. There really isn’t any time to sit back and get much rest because the next chapter in the 2017 Cotton crop is early season weed control and Cotton sidedress.

This term originated many years ago when farmers would apply fertilizer beside the cotton plants as the plants were growing to enhance their production. The fertilizer was applied as a band beside the row as a “sidedress” of nitrogen and other nutrients for the cotton plant.

I am often asked each year when Auburn recommends fertilizer applications for cotton.  For most soil types in Alabama, I recommend applying all of the phosphorus and Potassium, which has been recommended through an Auburn University Soil Test recommendation, at or just before planting.

Since Phosphorus will not leach, there is no reason to delay the application of this nutrient until later in the season.  It is also worth noting that Cotton doesn’t require a tremendous amount of Phosphorus to meet the plant’s requirements.

In other words, Phosphorus is important but the Cotton plant is not very responsive to Phosphorus fertilizers.  Potassium is much different.

As the plant matures and during the boll fill stage, which occurs from 25 to 50 days after the cotton flower blooms, the Cotton plant demands a good supply of Potassium.  Invariably, we will observe Potassium deficiency in Cotton every year.

Because much of the Potassium is Muriate of Potash and also because Potash isn’t subject to leaching like Nitrogen, I recommend applying the recommended Potassium at planting or just before.

Some farmers split apply potassium and this is certainly not wrong. However, I believe that much of this potassium might not become plant available soon enough to give the maximum benefit for that growing season, especially in a dryland situation.

Since Cotton is not a legume, like peanuts, in order to obtain maximum yields we must apply nitrogen fertilizer to the plant.  Generally we recommend 90 lbs. /ac of Nitrogen for optimal production, with the plus or minus 30 Lbs. /ac N depending upon soil type and crop history of rank growth or lack of growth on particular soil types.

Generally, sandier soils will require more nitrogen and heavier clay soils can produce effectively with lower rates of Nitrogen.

It is standard that 20 to 30 lbs. /ac of Nitrogen to be applied at planting to get the plant off to a good healthy start and the remaining amount to be applied at sidedress.

Generally I recommend applying sidedress nitrogen between the 5th and the 10th leaf.  This would be around a two week window during the plant’s life to meet this nutrient demand.  The reason being is because the plants will soon begin the reproductive life cycle and that is when the demand of Nitrogen will increase.

The first fruiting branches typically develop between the 5th and 7th node.  Varieties can influence which node the cotton plant begins a fruiting branch.

Dr. David wright, University of Florida Extension Agronomist, conducted a Nitrogen timing study a few years ago.  We are also conducting this test, with a similar protocol, on the Wiregrass Station in 2017.

For this test, there was a no nitrogen treatment compared with 60 lb/ac of sidedress nitrogen applied at different time intervals during the cotton plant’s life; 30 DAP (days after planting), 45 DAP, 60 DAP, 75 DAP, 90 DAP and 105 DAP.  The applications with the highest yields were obtained when applying the nitrogen between zero to 45 days after planting.

A delay in applying this nitrogen until peak bloom (90 DAP) was the equivalent of not applying any nitrogen at all.

Typically the cotton plant begins fruit set or squaring around the 40 to 45 day mark.  It takes around 21 days to develop the square until it flowers; which first flower is around 60 days of age.  The maximum yield is applying sidedress Nitrogen prior to flowering.

For these reasons, this management practice will determine the upper end yield potential just from a Sidedress Nitrogen Timing perspective as opposed to the amount of the product applied.  Therefore, it is better to be early as opposed to being late.

The results from Headland’s N Timing study will be available in the fall of 2017.



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