Early-season Cotton Fertility Needs and Impacts of Deficiency

Growers usually apply nitrogen and potassium fertilizers pre-bloom. But since squaring, bloom, and boll development are the times when cotton makes the largest fertility demands, a second fertilizer application is recommended where split applications are possible or a petiole test indicates additional requirements. Growers are urged to exercise caution, avoiding rates in excess of 100 pounds of nitrogen which may lead to excessive growth. The petiole nitrate-nitrogen level prior to flowering can be influenced as much by temperature as by soil nitrogen supply and is not considered a reliable measure until after flowering.

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Fertilizer Needs/Application Impact of Deficiency
Nitrogen Needs are highest during square set and bloom. Can be applied at planting, side-dressed through third week of bloom or foliar applied
  • Young leaves yellow or become pale green. As leaves age they develop shades of redress or brown, dry out and shed
  • Stunting of the plant
  • Reduced fruit set
Phosphorus Dependent on good liming program, must be placed in rooting zone
  • Stunted plants
  • Smaller leaves, dark green in color
  • Delayed fruiting and maturity
  • Reductions in lint yield and inferior fiber properties
Potassium Needs are high during boll fill. Subsoil levels are important, related to pH level, can be foliar applied.
  • Stunted plants
  • Veins of leaves redden before the discoloration spreads to the outside
  • Edges of leaves curl downward
  • Bolls are small and immature, may fail to open
  • Reductions in yield, fiber strength, and micronaire
Boron In mixed fertilizer or preemerge herbicides, common in limed fields
  • Abnormal shedding of squares and young bolls
  • Darkening of boll base
  • Small, deformed bolls that do not fluff normally
  • Terminal death and shortened internodes
  • Petioles display dark green ring
  • Leaves thicken, are dark green and hard to defoliate
  • Poor response to nitrogen and potassium
Sulfur MSoil applications are more effective than foliar. If planting behind peanuts that received gypsum, applications are not always needed.
  • Symptoms appear first in new leaves as persistent yellowing of new leaves and reddening of petioles
  • Severe cases can result in symptoms throughout the plant
  • Early diagnosis is critical because deficiencies after flowering starts to impact yield and late application cannot help recover that lint
Calcium Supplied through liming to meet high needs
  • Deficiencies are seldom seen as low pH and aluminum toxicity limit growth first
Magnesium Supplies through liming to meet high needs, deficiencies most likely on sandy soils
  • Appears first as purpling or reddening of lower leaves, veins remain green
  • Premature leaf shed

This article is from the Cotton Management Guide, a publication with year-round advice on managing high-yielding cotton. Download the Deltapine Cotton Management Guide now or sign up for new content to be delivered to your email each month.​​​​​​

Click here to learn more about determining normal cotton growth.