ABSTRACT
This study was conducted to formulate an in-season nitrogen (N) fertilization optimization algorithm (NFOA) to estimate midseason N rates that maximize corn (Zea mays L.) growth and minimize fertilizer inputs. Treatments included: a zero kg N ha−1; three treatments of 134 kg N ha−1 fixed rate applied in split, preplant, or sidedress; two treatments of 67 kg N ha−1 fixed rate preplant or sidedress applied; three NFOA-based midseason N rates (RI-NFOA, RICV-NFOA, flat-RICV-NFOA) with (67 kg N ha−1) and without preplant N; and two resolutions (0.34 and 2.32 m2) tested for RICV-NFOA only. With the 67 kg N ha−1 preplant application, midseason RI-NFOA-based N rates resulted in an N use efficiency (NUE) of 65% while the 134 kg N ha−1 fixed rate split applied had 56% NUE. Using the RICV-NFOA, NUE and net returns to N fertilizer were higher when spatial variability was treated at 2.32 m2 resolution.
Notes
±Date in month-day-year.
§Lake Carl Blackwell.
¶Sensing dates done between V8-V9 leaf growth stages.
§Determination of critical CV was based from plant population.
‡Average NDVI of NFOA treatments.
†Adjusted in-season response index, determined by dividing average Normalized Difference Vegetation Index (NDVI) between V8-V9 leaf growth stage of Treatment 6 (134 kg ha−1 preplant) by the Check plot. Adjustment was made using the equation (RINDVI× 1.64) - 0.528.
§Response index at harvest, determined by dividing the grain yield of the highest preplant N fertilized plots by the Check plot.
¥Critical CV used in the algorithm.
¶Determined from the equation: critical CV = (−0.0003*plant population) + 36.315.
¥Full description is presented in .
¥Full description is presented in .
¥Full description is presented in .
§Estimated by subtracting the grain N uptake of the check plot from the fertilized plot, divided by the N rate applied.
¥Full description is presented in .
‡Determined by subtracting the cost of fertilizer from the gross income (grain yield due to N fertilizer application × price per unit grain).
¥Full description is presented in .