Jim Fawcett, extension field specialist-crops in east central Iowa, reports that some corn fields are showing a deficiency of potassium (K). This deficiency in corn is frequently observed after a lack of rainfall in June. Symptoms are often seen first on ridge-till, then on no-till, and finally, if severe, on other tillage systems. Soil compaction aggravates the problem. K deficiency is more common in Kenyon-Floyd-Clyde and Clarion-Nicollet-Webster soil associations because both have low levels of subsoil K.
Tillage-induced potassium deficiency in dry weather.
Symptoms of K deficiency that are induced by dry weather may be somewhat different from classic symptoms of K deficiency. Classic K deficiency symptoms appear on the lowest leaves of the plant, first as yellowing at leaf tips, then progressing down leaf margins. Leaf margins turn brown as they die, and symptoms move progressively up the plant on the leaves.
Dry weather-induced K deficiency symptoms may not include necrosis (dying back) of leaf tips and lower leaf margins. For this type of deficiency, look for leaves in the middle of the plant to turn yellow at the tip as they become chlorotic (lose chlorophyll). The entire leaf eventually turns yellow, which produces a yellowish sheen to the plant except for newly-emerged leaves that are a normal green color.
If the plant is unable to take up K from dry soil, sufficient rain will allow the plant to resume normal growth, but existing deficiency symptoms will not disappear. If the problem is due to actual lack of K in the soil, the symptoms may continue to increase and result in a severe yield reduction.
There is no corrective treatment for this year's crop. If you see the symptoms described, sample and test the soil for K. Sample at different depths if you suspect that surface stratification of K is caus-ing the problem. Fall application of K in bands 6 to 8 inches deep in ridges can improve the next season's crop. A starter fertilizer treatment at planting also will help. For conventional tillage of chisel or moldboard plowing, broadcast K fertilizer before tilling should be effective on soils that test low for potassium.
This article originally appeared on pages 126-127 of the IC-476(18) -- July 15, 1996 issue.