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:
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.
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.