Winter Injury Stand Persistence and Potassium Fertilization

Richard Leep

Department of Crop and Soil Sciences

Michigan State University

In the past several weeks I have received calls on winter injury of alfalfa in several areas of the state.  In addition, I have been intensively monitoring 6 alfalfa fields for the past three years looking at factors affecting stand persistence.  One of the common themes I have heard from calls in the state regarding alfalfa winter injury is that it appears mainly on the side slopes of alfalfa fields.  In the fields we have been monitoring we have found where soil potassium levels are very low there was significant winter injury and stand decline.  In particular, where stand declines were most evident, the soil potassium levels ranged from 80 to 140 lbs/acre, which are very low.  We have also found classic foliar symptoms of potassium deficiency with white spots around the outer edges of the upper leaflets.  Potassium has a positive effect on nodulation and nitrogen fixation.  Alfalfa stand failure and subsequent takeover by grasses is sometimes an indication of low potassium in soils.  When potassium is low, an aggressive potash fertilizer program is necessary to obtain and sustain high yields of alfalfa.  High yielding alfalfa removes about 50 lb. of K or 60 lb. Of K₂O per ton of hay produced.  The first two photos (Figure 1 and 2) are taken in an area of an alfalfa field where low soil potassium levels were found show both stand decline and weed invasion as well as classical potassium foliar symptoms.  Figure 3. shows normal alfalfa growth within the same field.

            

Figure 1.  Alfalfa winter injury and                         Figure 2. Classic foliar potassium 
subsequent weed invasion.                                  deficiency found in the same area.

Figure 3.  A stand of alfalfa showing
good spring growth in the same field.