Improving Sample Collection, Sample Processing, and Laboratory Analyses for Corn Stalk Nitrate Test

Abstract

Core Ideas Corn stalk nitrate test results can help corn growers fine‐tune N management. Adoption of corn stalk nitrate test use can be enhanced with more practical field sampling protocols. Laboratory processing of corn stalk nitrate test samples can be simplified for reduced analytical cost. The corn (Zea mays L.) stalk nitrate test (CSNT) is a site‐specific, after‐the‐fact, diagnostic tool for N management of corn. Although considered effective, widespread adoption of CSNT is limited due to somewhat impractical sample collection, handling, and laboratory sample processing protocols. Five studies were conducted to evaluate the impact of alternative sampling, sample handling, and laboratory processing protocols on CSNT outcomes. Study 1 evaluated the effect of stalk length and position on CSNT values. In Study 2 timing of sampling or growth stage was evaluated. In Study 3 several sampling patterns within a field (samples taken within a corn row vs. perpendicular or under an angle to rows) were analyzed. Study 4 tested if (a) quartering of stalks, (b) delay in mailing of stalks to the laboratory, and (c) temperature during storage (refrigerator, freezer, room temperature) affected CSNT‐N. Laboratory grinding, extraction, and determination procedures were compared in Study 5. The results suggest that sampling protocols can be adjusted to include shorter stalk samples, taken within 5 d after silage harvest. Direction of sampling within a field did not impact CSNT‐N, eliminating the need for more labor‐intensive sampling. Also, quartering of stalks and different temperature during storage did not change CSNT‐N. Laboratories can use 2‐mm grinding, extraction with distilled water, and a nitrate specific ion electrode or flow injection analysis. We conclude that adjustments in sampling protocols and sample processing can be made, possibly increasing farmer acceptance of the test, and reducing the cost of sampling, sample processing, and laboratory analyses.