Aboveground Nitrogen Accumulation as a Function of Time in Corn and Winter Wheat.
Starr Holtz, Kefyalew Desta, Brian Arnall, Brenda Tubana, Roger Teal, Kyle Lawles, Clint Mack, Byungkyun Chung, Olga Walsh, and Bill Raun. Oklahoma State University, Ag Hall, Stillwater, OK 74078
Many researchers have documented crop nitrogen (N) uptake at various growth stages. The percent of total N uptake has ranged from 20% to 60% in corn (Zea mays L.) by the V8 growth stage. In addition many of the studies documenting N uptake in wheat (Triticum aestivum L.) and corn have been conducted but with limited number of sampling times. This study was conducted to establish the amount of N accumulated in corn and winter wheat over the entire growing season. Winter wheat samples were collected from two long-term winter wheat fertility trials located in Stillwater and Lahoma, OK. Forage samples were harvested from plots representing three N treatments 0, 45, and 90 kg N ha-1 at Stillwater and 0, 67, and 112 kg N ha-1 at Lahoma. A one square meter area of wheat was clipped from each treatment at growth stages: Feekes 4, 5, 6, 7, 10, 11, and harvest. For corn, sequential biomass samples were collected from 1.5 meters of row within three N fertilization rates (0, 112, and 224 kg ha-1) from a nitrogen fertility study established in 2006 near Stillwater, OK at growth stages: V6, V8, V12, VT, and R5. The comprehensive data on biomass and N content over growth stages of these two crops under limiting and non-limiting N conditions is very important to validate previous documentation on plant N uptake. Results from this study will assist in adjusting midseason fertilizer N rates based on predicted yields since nearly 50% of the total amount of N found in corn and wheat at maturity is accumulated at early growth stages.