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Here is some information from Chad Lee, University of Kentucky Extension Agronomist.
There has been some discussion about sidewall compaction with the understanding that farmers had to plant when they could plant and in some cases, this meant planting into fields that were a little too wet. Yesterday I visited a field where the farmer was concerned because the corn was “yellow and dying.” The county agent and I visited the field at the perfect time because a rain from the night before had kept the soils wet and improved the appearance of the corn.
The corn that was yellow exhibited typical potassium deficiency symptoms The farmer had applied 150 pounds of potash (90 lbs K2O) per acre prior to planting, so more than enough potassium is on the field. The problem was that the corn roots were growing along the sidewalls of the seed furrow created by the planter. Those roots could not get to the potassium which was near the soil surface (or the N and P also near the soil surface). The symptoms were more exaggerated because the dry weather also kept potassium from being moved to the roots. (Even if the potassium had been placed in a 2x2 band, the lack of water would have kept potassium from moving into the roots.) The good news is that the roots were pushing through the bottom of the furrow and a few roots were pushing through the sidewalls. A gentle rain will push more roots through the sidewalls.
Another dry spell could result in more symptoms of K deficiency. However, because roots were finding their way through the bottom of the furrow, I expect that these corn plants will do fine and the overall field is in relatively good condition. Where sidewall compaction was the worst, there were missing plants. The farmer said that the stand was perfect when the corn emerged, but then plants began to die. When digging in the soil, we did not find insects or wireworms. More than likely, roots from those plants were confined to the seed furrow and the hot, dry weather caused those plants to wilt and die.
The producer asked if a foliar fertilizer would help and then he said, “I tried one last year and it kept the plants green for about one week.” That makes sense. The use rates for most foliar fertilizers are such that the actual amount of nutrients being applied is very small. This very small amount of nutrients will result in a short-term greening of the plant. Dr. Murdock posted an article about temporary deficiency.Some of the foliar fertilizers on the market provide the appearance of “temporary sufficiency.” Instead of applying a foliar fertilizer, all that field needs is about one more good rain to help more roots break through the seed furrow. Once that occurs, the deficiency symptoms will disappear.