Could Potash Deficiency Show Up in Soybean Field This Late in Season? Symptoms are showing up on the newest trifoliate.

Reports of symptoms on soybean in the Beausejour, Plum Coulee areas and in dry beans near Gladstone (see photo “Potash Deficiency in Dry Bean”) that have Potash deficiency are showing up between previous crop swaths.

It can be difficult to diagnose Potash deficiency but the coincidences are strong when symptoms start showing up on the newest leaves when crops found occurring on lighter textured soils and during pod filling, as the leaves move Potash out of leaves into pods.  Potash starved leaves are quick to show symptoms once Potash is mobilized out of them. Potash deficiency in the late season is most seen in the upper leaves. 

 Other causes of late season yellowing:

  • Senescence – which we are seeing in some dry beans now
  • Drought – sandy soils may be worst – but these are also soils most likely low in K
  • Salinity – this is probably bigger than people recognize – seeing soybeans yellowing NOT in the lowest part of the field, but adjacent to these areas – typically where salinity rises out of the subsoil.  Likely these soils are not bone-dry – the plant just cannot squeeze any water out of saline soil
  • Iron chlorosis – which normally we see under excessively wet conditions.    

For the future, soil test and /or tissue test and compare good vs. poor areas and look at the levels of  Potash to determine if more is needed for future crops or early in the season to help the present crop.

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