Quantifying Temporal Patterns in Symptoms of Nitrogen Deficiencies in Corn by Remote Sensing.
Jun Zhang1, Alfred M. Blackmer2, Peter M. Kyveryga2, Mark J. Glady3, and Tracy M. Blackmer4. (1) Iowa State Univ (off-site), 2512 Hillsdale Dr, Dayton, OH 45431, (2) Iowa State Univ, Agronomy Dept, Ames, IA 50011, (3) Farmers Coop Elevator of Nickerson, 404 N Nickerson Rd., Nickerson, KS 67561, (4) Iowa Soybean Association, 4552 114th Street, Urbandale, IA 50322
Fertilizer-induced advance in growth stage for corn (Zea mays L.) is a potential source of errors when using symptoms of nitrogen (N) deficiency during vegetative growth to estimate amounts of fertilizer N needed for in-season correction of this deficiency. However, little attention has been given to the need to distinguish between a deficiency of N (a stress) and a symptom of N deficiency (a strain) as defined in modern discussions of stress-strain relationships in biological systems.We report studies showing that the effects of added N on advancing growth stage could be a significant source of errors in field-scale studies where remote sensing was used to diagnose deficiencies of N during vegetative growth. Additions of fertilizer N in early and mid June resulted in large differences in canopy reflectance (a symptom of N deficiency) that would be typically interpreted as an N deficiency. These differences in canopy reflectance, however, disappeared as the season progressed and yield responses to applied N were relatively small. There is a need to recognize that uptake of N and crop growth are dynamic processes, so good relationships should not always be expected between rates of vegetative growth early in the season and final grain yields.