Sidedressing Cotton

As cotton is squaring throughout the county, we need to also think about sidedressing. Here are some thoughts on sidedressing from the 2015 UGA Cotton Production Guide.

Nitrogen (N) Management

N can be very difficult to manage. Base N rates recommended by UGA Soil Testing Lab according to yield goals are blow:

YieldGoal-2015

These rates should be adjusted according to other factors:

  • Increase N by 25% if – Deep sandy soil, cotton following cotton, history of inadequate stalk growth.
  • Decrease N rate 25% if – Cotton following peanuts or soybeans, cotton yellowing good stands of winter legumes, history of rank/vegetative growth.

UGA Extension Scientist Dr. Glen Harris says our N rate should be applied in split applications since N is mobile in the soil. We want to apply 1/4 to 1/3 of recommended N at planting and the reminder at sidedress. Sidedress N between first square and first bloom. (If cotton is growing slow and pale green, sidedress more towards first bloom.) Sidedress N can also be applied as foliar treatments or through irrigation. No N should be soil-applied (including pivot) after 3rd week of bloom.

Phosphorus (P) & Potassium (K) Management

P & K need to be maintained in the upper medium range by soil testing. All of the P requirements should be applied preplant since it is relatively immobile in the soil and important to seedling growth. K should also be applied preplant on all soil types including Piedmont, Coastal Plain, and Deep Sand soils. Split applications of K have not proven to be effective ton Tifton type soils. Recent field trials in GA have focused on additional soil-applied K during N sidedressing versus foliar K during peak bloom (4 weeks bloom). Dr. Harris says results on Coastal Plain soils indicate that foliar K may be more effective than sidedress K in improving yield.

StemphyliumLeafSpot (2)

Stemphyllium Leaf Spot

Currenty, foliar K applications should automatically be considered on deep sands, low K soils, high Mg soils, high=yielding conditions, short season varieties and where K deficienes have occurred. Cercospora, Alternaira and Stemphyllium leafspot have all been linked to K deficiency. They are secondary to K deficiency. Corynespora leafspot does not appear to be linked to K.

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