Limitations of the Cornstalk Nitrate Test in Irrigated Corn Production Systems.

The Corn Stalk Nitrate Test (CSNT) is a post-season nitrogen (N) management tool developed in the upper Midwest and used to determine if low/optimal/excessive N was applied to the corn (Zea mays L.) crop during the current year. Corn plants can take up more N than needed for maximal production without displaying visual evidence. At maturity, corn plants receiving excess N will accumulate NO₃-N in the lower portion of the corn stalk. However, corn plants that received inadequate amounts of N will remobilize NO₃-N from the lower portion of the stalk and leaves to assist in grain-fill. Interpretation of CSNT results can help adjust the N recommendation for subsequent corn crops and help fine-tune N management for a specific field over time. Due to the differences in production methods and environmental conditions throughout the growing season, the objective of this study was to determine the applicability of the CSNT in a furrow-irrigated corn production system. Corn stalk samples were collected from 26 site-years of N response trials within 2 wks following black-layer formation of furrow-irrigated corn in Arkansas. Results of this study indicate that the critical concentration level for the Low category set by the upper Midwest is adequate for a mid-South corn production system (Low: <250 ppm). Some treatments with Low NO₃-N concentrations still produced >95% relative grain yield, indicating a high N use efficiency and not the need to apply more N fertilizer. However, all treatments with an average NO₃-N concentration >700 ppm achieved ≥ 95% relative grain yield which suggests that the upper end of the Optimal concentration range could be lower than what was determined in the upper Midwest. Our results also display less variability in stalk NO₃-N concentrations than the upper Midwest potentially as a result of differences in N fertilization timing and irrigation.