June 17, 2011

Greater than normal May rainfall and cooler than normal May temperatures in northeast Nebraska have combined to create conditions that are causing corn in some areas to be yellow. One field that I visited had nearly normal green corn, with areas of yellow corn with some purpling of the leaf sheaths and some leaf margins. The plants showed some stripping with the leaf veins pale green and the intervein area yellower. The field had a fair amount (185 lb/ac) of 11-52-0 fertilizer applied in the fall, in a band that was tilled in about a foot wide band in an otherwise no-till continuous corn field (three years).

A modest amount of fertilizer (5 gallons, approximately 6-24-6) was applied in-furrow at planting. Ten days after planting 70 gallons of 32% UAN was applied. The yellow areas were in light colored sandy soil while the green corn was in sandy loam soil. No samples were taken from the soil or the plants.

The questions are:

• What is the problem?
• What should be done about it?

Diagnosis

The purple color could be a phosphorus (P) issue, but some hybrids show this regardless of whether there is a phosphorus deficiency. It looks like there should have been enough P applied in the fall and in the spring starter for this crop so the purpling could indicate poorer root growth and lack of P uptake. There were no soil tests to determine the existing level of phosphorus prior to the applications.

Yellowing could be due to a deficiency of nitrogen or sulfur (S) or both. Given the rainfall it is possible that the nitrogen had leached below the roots. Also, no sulfur was applied and the soils appeared to be both sandy and low organic matter. Both conditions would warrant sulfur application. In addition, this spring’s cool weather likely decreased sulfur mineralization from the soil organic matter. Also, in continuous corn this would be slower to break down than in tilled ground or following soybeans. Corn grown in the neighborhood that followed soybeans generally looked better, as did tilled fields. The sandy soil has lower soil water holding capacity and probably less residual nitrates so the more than 5 inches of rainfall would move the nitrogen deeper into the profile where the roots have not yet grown.

Recommendations

1. Short Term: A deep soil test (to 48 inches) would resolve how deep the nitrogen had moved, but that was not taken, and the farmer wanted to do something the next day. The field was to be sprayed with glyphosate so liquid products were preferred. Given that an immediate decision was needed, I recommended applying 15 lb of sulfur per acre with 5-10 gal of UAN. The field probably could use the sulfur, and the added nitrogen will help the plants grow until they reach the leached nitrogen.  If more rain comes in excess of ET, another nitrogen application may be necessary later in the season.

2. Long Term: Due to the variable soil texture in the field, some sort of intensive sampling should be conducted to determine texture, organic matter, pH, P, K, and Zn. Future fertilizer application could add nutrients where needed. Applying the sulfur with the starter is good; however, the planter is set up with an in-furrow applicator so using this method would limit the total amount of nutrients applied.

Charles Shapiro, Extension Soils Specialist
Haskell Agricultural Laboratory, Concord

Note: The recommendation in this story was updated June 24,  2011.