Sampling corn stalks this fall will likely be later than normal due to the delayed planting in many Iowa cornfields. The overall suggestion is to wait until crop maturity, and sample within 1-3 weeks after kernel black layer. This does not work well for silage corn, so the suggestion is to collect stalk samples at the time of silage harvest or within 24 hours after harvest (as long as no rain between harvest and sampling). The publication describing the End-of-Season Corn Stalk Nitrate Test was updated in 2018 (Use of the End-of-Season Corn Stalk Nitrate Test in Iowa Corn Production, CROP 3154). That publication describes the sampling protocol and interpretation of results. The old interpretation categories were adjusted; now three categories of Low (< 250 ppm), Sufficient (250-2,000 ppm), and High (> 2,000 ppm). As noted before, the most reliable interpretation is with High concentrations (> 2,000 ppm) indicating more than enough plant-available nitrogen for that year. Also, as noted before, don’t base nitrogen management changes on only one-year results; instead sample multiple years to build a trend database. The stalk segment to sample remains the same, an 8-inch segment from 6 to 14 inches above the ground. Avoid sampling odd plants or plants damaged by disease or insects. Collect 15 stalk segments per sample area. Place stalk samples in paper (not plastic) bags. If needed, refrigerate until taking or shipping samples to the lab.
Antonio Mallarino Professor of Soil Fertility and Nutrient Management, Extension Specialist
Dr. Antonio Mallarino is a professor of agronomy and nutrient management research and an extension specialist at Iowa State University. His programs focus on agronomic and environmental issues of nutrient management with emphasis on phosphorus, potassium, lime, and micronutrients. Issues addresse...