Nitrogen is often the most limiting nutrient in corn fields, especially in wet seasons or after big rains when nitrogen is lost by various means. Losses are also more likely if nitrogen is applied in the fall, even with N-Serve, and if it's applied in March before planting.
Bob Nielsen says plenty of nitrogen deficiency symptoms showed up in fields in 2010. Much of that was related to ponding in central and north-central Indiana that occurred in mid-June.
The symptoms of severe nitrogen deficiency are obvious- stunted yellow plants with small ears indicate there wasn't enough N available. More subtle symptoms that begin to show up as crops run short on N include yellowing which begins on the lower leaves, and shows a V-shaped pattern from the tip back down the center of the leaf.
For those who scouted closely, last year and in almost every recent year, other symptoms may have showed up in some fields. If the edges of lower leaves turned yellow, starting at the tip, instead of yellow running down the middle of the leaf, it's most likely a sign of potassium deficiency in corn.
Potassium deficiencies have become more common in both corn and soybeans in recent years. It's important to test soils to make sure that soil test levels are at least adequate to produce a good corn crop. It's especially important in silage fields or fields where corn stalks are baled and removed. Much of the potassium winds up in the stalk. If stalks are left on the field, break down of the old tissue eventually results in returning potassium to the soil. If residue is removed, then higher applications of potassium fertilizer, or else livestock manure, may be needed.
Soil sampling during the dry fall became an issue for several reasons, including the inability to get soil cores at a consistent depth. One test that may show lower than it really is would be potassium, assuming tests were pulled while the soil was very dry. The pH reading may also be lower than normal. Phosphorus readings likely won't be affected.
If you had soils sampled this past fall during the dry spell and potassium readings are lower than in previous years, or lower than they should be based upon crop removal, don't panic. It's likely due to the effect of sampling in very dry conditions. However, by the same token, if potassium levels were borderline before and are borderline or in the low category this time, you may need to apply potassium fertilizer for optimum yields.
And if you've read this far, you've just found another answer to the Crops Knowledge Quiz sponsored by Indiana Prairie Farmer and Beck's Hybrids. Question #8 reads: Yellowing and dying of leaf margins on lower corn leaves starting at tip could be deficiency of: a) potassium, b) nitrogen, c) phosphorus, d) chlorine. The answer is 'a,' potassium.
Remember you can find all the questions in the December issue of Indiana Prairie Farmer, either in print or on this Website, under 'More Indiana Prairie Farmer' and 'Magazines online.' Entries are due either postmarked or emailed by Jan. 15.