Tuesday, November 14, 2006 - 3:30 PM

Effect of Delayed N Fertilization on Corn Grain Yields.

Olga Walsh, Arthur Klatt, John Solie, and William Raun. Oklahoma State Univ, Ag Hall, Stillwater, OK 74078

Determining optimal timing for nitrogen (N) fertilizer application is one of the key challenges that crop producers are facing. Three experimental sites (Efaw and Haskell – rainfed land; Lake Carl Blackwell – irrigated land) were established in 2005 to evaluate the effects of delayed N fertilization on corn grain yield and nitrogen use efficiency (NUE). A randomized complete block design with three replications was employed for this study. Four preplant N rates (0, 45, 90 and 180 kgha-1) and three sidedress N rates (45, 90 and 180 kgha-1), applied at three growth stages (V6, V10 and VT) resulted in fourteen treatment combinations. Highest NUE’s were achieved with mid-season N fertilizer application. Crop recovered from the stress imposed by nitrogen deficiency when 45kg ha -1 preplant has been applied followed by sidedress before or at V10. Higher grain yield was achieved for LCB and Haskell sites for the treatments with 45 kg ha -1 preplant, when topdress of 45 kg ha -1 has been applied at V6 compared with sidedress of 45 kg ha -1 at V10. For the Efaw site the situation was reversed, but the difference in grain yield was not significant. Only at Haskell the significant increase in grain yield was achieved when 90 kg ha -1 sidedress at V6 was coupled with 90 kg ha -1 preplant. At two other sites there was no significant difference in grain yield associated with the time of application of 90 kg ha -1 sidedress. Corn did not recover when no preplant was applied if sidedress N was delayed until VT. Based on the first year of data, sidedress application at or before V10 can be recommended as the optimum timing for midseason N fertilization in corn, coupled with the minimum of 45 kg ha -1 N fertilizer applied preplant.