Corn planted early in the year often yields better than late-planted corn, but it can also be hindered by unfavorable weather. This year, cool and wet conditions early in the season have stressed plants and slowed root growth. As a result, the N.C. Department of Agriculture and Consumer Services reports that many fields now show evidence of nutrient deficiency, especially of phosphorus and sulfur.
Corn plants that are purple because of phosphorus deficiency are showing up even in fields where recent soil-test reports show phosphorus levels to be adequate. The reason is poor root growth rather than lack of fertilizer, and the plants will probably outgrow the problem, said Dr. David Hardy, chief of the department’s Soil Testing Section. Sulfur problems, usually typified by yellow plants, might pose more of a challenge.
Hardy offers advice for addressing nutrient deficiencies: “Based on experience with early-season problems, I believe it is always best to collect and submit plant tissue, soil and nematode samples to rule out possible concerns and specifically identify the causes of growth disorders. On sandy soils, corn may be yellow and nutrient-deficient, but the ultimate cause could actually be plant-parasitic nematodes.
“Problems should not be addressed based on visual observation alone,” Hardy said. “Growers receive the best diagnosis and recommendations if they submit matching samples from ‘good’ and ‘bad’ areas and completely fill out the diagnostic sample information form associated with each type of test.”
Hardy urges growers who see problems to submit diagnostic samples even if they have a fairly current soil report. Sulfur can leach quickly from the crop root zone, and soils that tested sufficient for sulfur three months ago could now be low.
“Even fertilization programs that include sulfur may not be providing enough to correct or prevent deficiency,” Hardy said. “A combination of soil and plant tissue samples can provide a clear diagnosis of the problem and how to address it. It is not enough to know which nutrient is deficient. Growers need to know how much to apply.”
When submitting diagnostic samples, growers should provide as many details as possible about crop history and symptoms. For instructions on filling out paperwork, visit the Agronomic Services Division website, www.ncagr.gov/agronomi, and select the “Diagnosing Plant Growth Problems” link. If multiple types of samples are submitted, then each must be packaged separately and addressed to the appropriate laboratory section. Diagnostic samples receive priority and are processed as quickly as possible.
The division’s regional agronomists are available to provide advice on how to collect and submit agronomic samples and alleviate nutrient problems. For contact information, visit www.ncagr.gov/agronomi/rahome.htm