Potassium fertility in cotton is pretty well understood. Our prime farmland has good residual levels such that we are in maintenance programs to replace what our crops are removing.
A big area of focus relates to the soil types and in particular, the accessibility of a crops root system to underlying clay. Our clay subsoils are the storage point for nutrients with positive charges including potassium.
Even if we get some leaching rain, the clay will hold on to the potassium and allow us straight forward approach to K fertilization with one primary application that can be made prior to planting up to about the 4 leaf stage. I believe we have 75% of our soils that have clay accessible by the root system and is considered our Prime Farm Land.
The challenge really comes from our deep sands that do not have any clay subsoil underneath them, at least not close enough for the root system to practically reach it.
Soil names like Uchee, Bibb, Rumford, Ocilla, Tarboro, Kenansville and Bojac by definition do not have any clay within reach of a shovel or maybe even an excavator but certainly not a cotton root. These soils probably account for 25% of our soils (certainly are in parts of at least that many fields) and are more common in close proximity to rivers.
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As a result, we find a benefit from splitting the potash, or at least applying some or all of it after planting but still early enough for rainfall to activate it before cotton gets too big.
This idea fits well for farmers that are already adding multiple nitrogen splits to their fertility program particularly blended with ammonium sulfate for part of the nitrogen. I think these soils are where we see the ‘light land syndrome’ in the summer after heavy rainfall or during drought and addressing this potassium challenge accounts for a third of the problem.