Potassium Deficiency Symptoms in Dry Beans and Soybeans

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)