If your corn is yellow and standing in water, the obvious conclusion is it is short on nitrogen. Chances are the soil is too waterlogged for the roots to function properly and feed the plant. Based on past experience, when the water goes away some nitrogen will be left. The question will be how much.
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Dave Nanda, consultant for Seed Consultants, Inc., looks for classic examples of nitrogen deficiencies when scouting corn fields.
"Look for light brown firing which stat at the tips and works back to the midrib of the leaves," he says. "Firing will usually start first on the bottom leaves of the plant. If conditions aren't completely waterlogged, the plant may still be able to get enough nitrogen and supply the rest of the plant," he says.
He has been in good-looking corn fields not as affected by flooding where there was still some firing on the lowest leaves. However, in most cases the plants looked good. The question will be if there is enough nitrogen left in the soil even there for corn to reach its full potential later in the season when ear development happens and kernels begin to fill.
Sometimes some people confuse nitrogen deficiency with potash deficiency. Once not a problem, especially in eastern Corn Belt states, potash deficiency has shown up more often lately where farmers have spent years concentrating more on nitrogen and phosphorus spoil fertility and not paying as much attention to potassium.
Potassium deficiency symptoms tend to start near the base of the leaf and work out toward the tip. One way to look for potassium deficiency is to pull tissue samples. Soil samples can also help pinpoint phosphorus, potassium and micronutrient deficiencies.
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What's likely to show up more often this year, however, especially where soils were saturated for long periods of time, is nitrogen deficiency, resulting in classic yellowish leaf symptoms, and in severe cases, yellow, stunted plants.