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Abstract
Portable chlorophyll meters have been reported to provide a new tool to rapidly assess the nitrogen (N) status of growing crops, but need further validation. This study was conducted on growers’ fields to determine if the portable chlorophyll meter is an accurate tool to monitor the N status of irrigated corn (Zea mays L.), thereby allowing producers to make in‐season N application decisions. Results indicate that the chlorophyll meter can be used to separate N responsive from non‐responsive treatments, but it is sensitive to differences in corn hybrid. Chlorophyll meter readings at the 6‐leaf (V6) growth stage were not correlated with final grain yield. However, meter readings at the tasseling (VT) growth stage were predictive of grain yield response at seven of eight research sites. Optimal reading times for in‐season N management were at the V10 and VT stages. Variability in leaf greenness requires a careful sampling technique and a sample size of approximately 30 leaves per field to accurately determine N response. The portable chlorophyll meter can be used to diagnose N sufficiency in irrigated corn, but soil tests are needed to determine the actual amount of N required. Our results indicated that when chlorophyll meter readings are less than 95% of a well‐fertilized reference strip within the same field, additional fertilizer N is warranted.