Late Season Nutrient Deficiency/Fertilizer Applications in Cotton

Generally speaking as we approach this time of year, the discussion in cotton turns to irrigation termination.  However, given that we are about 10-14 days later than “normal” numerous questions are still be posed regarding late season fertilizer applications.  A number of points should be considered.  After peak bloom, cotton fertility demands begin to go down compared to cotton at peak bloom.  The nutrient demand for nitrogen and potassium during peak bloom in particular is heavy.  In many cases, nutrient demands from cotton with a heavy fruit load exceed that which can be supplied in a timely manner especially during peak bloom.  I equate this to you or I working outside and needing a drink of water.  A large cup of water (or the soil in the case of cotton) has what we need; however, if we are drinking from a straw (or the root system of a cotton plant) it is difficult to get as much water as we would like in a timely manner.

Additionally, for cotton with a shallow root system, water and thus nutrient uptake may be limited due to limited root mass.  If you are witnessing nutrient deficiency symptoms, examine the root system of your plants.  If they appear shallow this could be the source of the symptoms on the plant.    Shallow roots have been a common occurrence this year given all of the moisture early in the growing season.

Lack of water – many areas have experience several weeks of dry weather.  If irrigation is not an option and you have experienced very dry conditions, nutrient deficiencies could be tied to lack of water and subsequent nutrient uptake from the soil.

In some cases, you may truly have a nutrient deficiency in your soil.  If this is the case, bolstering your soil fertility program will likely help to maintain, if not improve your yield goals.

What To Do:

In nearly all cases, I would not recommend a foliar fertilizer application.  For the most part, the amount of fertilizer being applied in foliar products will only provide enough fertilizer to supply plant demands for 1-2 days if all of that material gets into the plant.

Dry fertilizer applications – I would not apply additional nitrogen at this point.  Excess nitrogen can delay maturity and the last thing I want to see is further delayed maturity on an already late crop.  With regard to potassium, I wouldn’t count on potash application to increase yields this season; however, potash applications may build your soil test levels for next year which could be beneficial.

One final point, foliar diseases are making their appearance which has become common.  In many cases onset of these foliar diseases coincides with a potassium deficiency in the leaves in which the disease appears.  These foliar diseases are generally not yield limiting; however, the jury is still out on target spot at this point depending on the severity of infection and subsequent defoliation.  Tom Allen, myself, and others have conducted numerous fungicide trials in cotton and never observed a benefit from fungicide applications in the presence or absence of foliar disease.  Again, the one caveat to that is target spot – the jury is still out on benefits of fungicide applications for this disease.