Potassium Deficiency in Cotton

Cotton is blooming throughout Mississippi and a large portion of the crop is in good to excellent shape.  In addition, fruit retention is very good in most cases.  Once cotton begins to square and progresses into bloom, nutrient demands alter dramatically.  When cotton is blooming, plant demand for potassium can be as high as 4 lbs per acre per day.  In addition, cotton is somewhat more sensitive to potassium deficiency than some other crops and may show signs of potassium deficiency in soils that have no history of low potassium levels.  Furthermore, the complex of foliar diseases that have become common in cotton production in Mississippi are often associated with potassium deficiency.  If you have been applying potassium fertilizer at levels determined through routine soil sampling and are still observing potassium deficiency, the following may be contributing to this:

1.  Potassium deficiency – In soils that are potassium deficient, chlorosis may be a result of this deficiency.  The reason this does not appear sooner in the season is due to cotton’s demand for potassium.  Cotton demand for potassium is relatively low until square appear at which time demand begins to increase.
2. Dry weather – Dry weather can cause potassium deficiency to appear if there is minimal moisture in the soil profile for the plant to take up water and potassium.  In this situation you may have more than adequate soil test levels of nutrients.
3. Hard pan – if you have a hard pan and subsequent limited root growth, the pool from which the plant can pull water and nutrients becomes limited.  Again, you may have adequate soil test nutrient levels; however, if there is limited water and/or root growth nutrient availability may also be limited.
4. Low pH – if you have low pH soils (i.e. below 5.8) you likely have restricted root growth to some degree.  Restricted root growth will limit the area from which the plant can take up water and nutrients.
5. Nematodes – if you have high levels of nematodes that are limited water and nutrient uptake this can also contribute to chlorotic coloration in cotton.
6. Supply/Demand – In some cases, the plant may need more potassium than it can physically take up from the soil.  This may be the case where cotton is blooming and is maintaining a heavy fruit load.

Potassium deficiency often appears initially as interveinal chlorosis following by red coloration of leaf tissue on older leaves.  After peak bloom, similar deficiency symptoms appear but tend to appear on new growth.  If deficiency symptoms become severe enough, leaves can curl downward and/or appear thickened.  In extreme cases, cotton will begin to defoliate itself due to potassium deficiency.