Tiller contribution to spring wheat yield under varying seeding and nitrogen management

Hard red spring wheat (HRSW) (Triticum aestivum L.) grain yield is comprised of the combined production of the main stem and tiller spikes. Experiments were conducted under dryland (Casselton, ND) and irrigated (Carrington, ND) conditions from 2003 to 2005 to determine tiller development and the relative contribution of main and tiller wheat spikes to final grain yield undervarying cultivar, seeding rate (SR), N rate, and N timing. The experimental design was a randomized complete block design (RCBD) with a split-split plot arrangement with four replicates. Treatments consisted of a factorial combination of HRSW cultivars (Alsen and Granite), SR (2.9 and 4.2 million seeds ha(-1)), N levels (140 and 224 kg ha(-1) for the nonirrigated site; 168 and 280 kg ha(-1) for the irrigated site), and N timings (preplant, 2-split, and 3-split). Increased SR significantly increased stand count. The lowest SR and N level significantly increased tillers m(-2), while the 3-split N timing treatment significantly reduced tillers m(-2). Increased N level and SR significantly increased spikes m(-2), while the 3-split N treatment significantly reduced spikes m(-2). Cultivar, N level, and N timing main effects did not influence the relative contribution of the main spike and primary tillers (T1, T2, and T3) spikes to grain yield. Increasing the SR increased the proportion of yield from the main spike and decreased the proportion from the T2 spike. For environments where fewer tillers are desired, SR appears to have the largest impact on tiller numbers without negatively influencing yield.