Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu
Potassium (K) deficiencies have been showing up in a few of our fields. Like nitrogen (N), leaves will start to yellow at the bottom of the plant, but the yellowing should extend along the edges of the leaf (Figure 1). Nitrogen can start at the tip and extend down the mid-rib, causing a V-shape. If you catch it too late, the entire leaf may be yellow or dead, but other leaves in the area should share these same features. This has not been a typical deficiency for us, since our soils have some minerals that provide additional K, on top of fertilizer additions.
This year drought conditions may exacerbate and cause K deficiencies. We need moisture to help K move to the plant, and it may have also reduced mineral weathering and release of K. Rainfall through June was lower, particularly in the northern end of Delaware (Figure 2). When rainfall is totaled through July 4th, New Castle County has accumulated much more precipitation (Figure 2). This map doesn’t account for rainfall intensity, which limits infiltration into the soil.
It appears the most consistently dry part of the state is a band from Harrington to Milford, which had lower rainfall through both June 1st and July 4th, compared to the rest of southern DE. All of these drought prone regions may be good places to scout for K deficiencies. While our research fields have been irrigated, these deficiencies have still appeared around the V9-V12 stages. Soybeans have so far shown no visual signs. It would be a good year to examine your soil types, fertility program, and rainfall to see where K issues may exist for you.
The best way to determine the issue would include tissue and soil tests. These visual examples are good indicators, but do not necessarily determine why the issue occurred. We have studied K deficiencies along dry corners of center pivots in 2021 and 2022 and seen no problems when K was adequate. This season could provide us with additional information on how soils, irrigation, and management interact with K availability.
Figure 1: Potassium deficiencies starting at the bottom of the corn plant along the leaf edges.
Figure 2: Rainfall accumulation from April 25th to June 1st and April 25th to July 4th.