Nitrogen is still the 800-pound gorilla when it comes to corn nutrition. But it’s now joined by several other nutrients, even some secondary and micronutrients, which can be limiting enough in some situations to affect yield. Part of this change may be due to farmers striving for higher yields. Crops consultants like Joe Nester, Nester Ag, Bryan, Ohio, say Clean Air Act laws resulting in less sulfur in the air and raising the pH of rain have also played a role.

You can find symptoms of nutrient deficiencies in the Corn & Soybean Field Guide published by the Purdue University Crop Diagnostic Training and Research Center. Corey Gerber, a Purdue Extension agronomist and director of the center, notes they also just released the Corn Field Scout app for iPhones and Android cellphones. Soybean Field Scout is also available. These apps cost $5.99 each.

Here are symptoms for seven deficiencies you could find in corn this year. Descriptions provided here are from the Corn Field Scout iPhone app.

1. Nitrogen. Younger plants with nitrogen deficiency may be stunted and spindly, with light-green or yellowish-green color. Older plants show traditional V-shaped yellowing on older leaves. It starts at the leaf tip and progresses down the midrib.

2. Phosphorus. Low levels in the soil is an obvious cause of phosphorus deficiency, but cold soils, wet soils, or dry and compacted soils can limit how much phosphorus roots can find, producing a deficiency in the plant. Early symptoms include stunted, dark-green to bluish-green plants with purpling or reddening of tips and leaf margins.

3. Potassium. Yellowing leaf margins on lower leaves, beginning at the tip and running around the margin, is a symptom of potassium deficiency. Plants may wilt easily, especially in full sunlight.

4. Sulfur. Young plants deficient in sulfur will be stunted, spindly and light green in color. Upper leaves will become light green first. Interveinal yellowing or leaf striping is a key symptom.

5. Magnesium. Symptoms for magnesium deficiency are most likely to appear on sandy, acidic soils in high rainfall areas, where soil tests are less than 100 pounds per acre for magnesium, where soil exchangeable potassium levels are high, and where a high rate of ammonia was applied on soils with low magnesium levels.

Look for yellow to white interveinal striping in young plants. Beaded streaking of dead, round spots may appear. Older leaves become reddish purple. Actual symptoms expressed for this deficiency — or any deficiency — are heavily tied to weather conditions. Confirm suspected deficiencies with tissue tests.

6. Manganese. Light-green or olive-green leaves may indicate a problem with manganese. Look for a slight yellowish stripe on upper leaves. Manganese deficiency is most common where manganese soil test levels are low and soil pH and/or organic matter levels are high, in low areas of fields, and in organic sands, peats and mucks.

7. Zinc. Low soil levels combined with high pH or high phosphorus levels may produce symptoms of zinc deficiency. You may also see problems with zinc on cool, wet soils with low organic matter, when it’s cloudy early in the season, and if soil compaction affects rooting.

Classical symptoms are white, interveinal strips extending from leaf base to leaf tip. Leaf edges, tips and midribs stay green.