| dc.description.abstract | Nitrogen Use Efficiency (NUE) for maize (Zea mays L.) production is low in the developed and developing world. Nitrogen application rates both preplant and sidedress need to be adjusted based on variables such as the environment, peak demand, and field-to-field variability which are known to change from one year to the next. This study was conducted to determine the minimum up-front fertilizer N rates, needed to improve mid-season fertilizer N use efficiencies, and determine periods of maximum N demand. Four field experiments were conducted where N as urea ammonium nitrate (UAN, 28-0-0, N-P-K) was applied preplant at rates of 0, 17, 34, 51, 67, and 168 kg N ha-1. Preplant fertilizer was applied on April 6 for EFAW and Perkins, and April 7 Lake Carl Blackwell. Normalized difference vegetative index (NDVI) data were collected from the V6 to V10 growth stages. At V6, sidedress N was applied at rates of 168 kg N ha-1 for treatments 8 through 14. Due to faculty-design-treatment-structure errors, this maize N study will be conducted in the 2017 growing season. This study will determine the minimum preplant N rate needed combined with sidedress N for maximum yields in maize. Grain sorghum (Sorghum bicolor L.) production similar to Maize (Zea mays L.) needs to take place at much higher levels of nitrogen use efficiency (NUE) than it is achieved today. Nitrogen application rates, both preplant and sidedress, need to be adjusted based on variables such as the environment, peak demand, and field to field variability which are known to change from one year to the next. This study was initiated to determine the minimum pre-plant fertilizer N rates needed to improve mid-season fertilizer N use efficiencies, and to determine periods of maximum N demand. Two field experiments were conducted where N as urea ammonium nitrate (UAN, 28-0-0, N-P-K) was applied preplant at rates of 0, 17, 34, 50, 67, and 101 kg N ha-1. Preplant fertilizer was applied on April 6 for EFAW, and April 15 for Lake Carl Blackwell. Normalized difference vegetative index data were collected at 512, 732, 1080, and 1341 total degree day heat units. At 830 total degree day heat units, sidedress N was applied at a rate of 34 kg N ha-1 for treatments 7 through 12. The preplant N rate for these studies was 67 kg N ha-1 (Tables 6 and 7). In order to maximize yields, at least 34 kg N ha-1 applied sidedress was needed. | |
