Cotton Potassium Deficiency - Cosmetic or Real?

Visual potassium deficiencies in cotton have recently been observed with increasing frequency and over a wide range of circumstances in Louisiana, on soils historically understood to contain adequate levels of potassium for cotton production. It is unclear to what extent these symptoms are linked to variety selection, and to what extent the apparent deficiencies are a factor in limiting yields. The objective of this study was to determine yield response to applications of potassium fertilizer in a field pre-determined by soil test to have medium to high levels of soil potassium. Three cotton varieties (DP 0912, ST 5288, and PHY 499) were selected and planted on a Commerce silt loam in the Louisiana Delta. Treatments included no potassium fertilizer, 44.5 kg K ha-1, or 89 kg K ha-1 applied as granular muriate of potash, pre-plant surface broadcast.  Additional treatments included either no foliar potassium, or 8.9 kg K ha-1 applied at first bloom, first bloom plus 2 weeks, and first bloom plus 4 weeks (total  26.7 kg K ha-1) as potassium nitrate dissolved in solution. All treatments were replicated 4 times in a Randomized Complete Block design. Soil samples were extracted prior to fertilizer application. Leaf tissue samples were collected at first bloom plus one week, first bloom plus 3 weeks, and first bloom plus 5 weeks and analyzed for potassium content. Visual potassium deficiency symptoms were recorded as observed. Plant mapping for presence of first, second and third position bolls was conducted prior to harvest. Yield, turnout and quality parameters were collected.