Corn (Zea mays L.) requires higher rates of nitrogen fertilizer than any other major U.S. crop partly because N fertilizers are subject to loss through various mechanisms. Because of this, corn may suffer from inadequate nitrogen fertilization or producers may over-apply nitrogen to compensate for early-season nitrogen losses. A timely, accurate, and precise method for measuring in-season corn N status is needed to allow producers to keep nitrogen use efficiency high within a growing season.
Using appropriate software, hue, saturation, and brightness values of digital images can be combined in a dark green color index (DGCI) which is closely associated with leaf nitrogen concentration. Our objectives were: (1) to develop quantitative relationships among yield, corn leaf nitrogen concentration, and DGCI measurements taken in the mid-vegetative stages of growth development;; and (2) to determine the amount of nitrogen to apply to recover yield based upon DGCI measurements on 6-leaf corn (V6).
Various corn hybrids were planted across two years in Arkansas. A wide range of N applications were made at emergence and at V6 stage. SPAD, DGCI, and leaf nitrogen measurements were taken prior to V6 application and again at tasseling. Leaf nitrogen concentrations, DGCI, and SPAD were found to be closely associated. Crops with varying early-season N deficiencies demonstrated a non-linear, quadratic response to V6 N applications. Combining the responses of yield to V6 N application amounts with concurrent mid-season DGCI measurements allowed for the development of calibration equations. These calibrations equations allow corrective, mid-season N applications to be made based on an observed DGCI value, which allows for the recovery of 90 or 95% of the crop\u27s yield potential
