Along with many other challenges associated with dry conditions this crop season, potassium (K) deficiency symptoms are being expressed in crops including dry bean and soybean. The image shows K deficiency symptoms in pinto bean from the Carrington REC dryland dry bean variety trial. The dry bean plants have been translocating K from older leaves to upper leaves and pods for seed development, and plants lacking sufficient K are displaying leaves with yellow or chlorotic edges.
Extended dry soil conditions reduce K availability, with deficiency symptoms likely with soil K levels below soil test critical values and especially with soil clay chemistry having smectite-to-illite ratio greater than 3.5.
In addition to the fixation/retention of K in smectitic clay interlayers, the lack of soil water forces plant roots to only encounter K through direct contact or diffusion. Both of these processes limit the volume of soil with possible plant-available K that can be taken up. In moist soils, K is released from smectitic clays and some K movement is possible with soil water to the roots.
Details on K management (soil testing and K fertilizer application) can be found in NDSU Extension circular ND Fertilizer Recommendation Tables and Equations.
(Source: Greg Endres and Dave Franzen, NDSU Extension)
