Plant and soil responses to source, rate, and timing of applied N for plains bluestem production

In western Oklahoma, one of the most popular grass species being used for p astureland is Plains bluestem (Bothriochloa ischaemum L.). Despite the curr ent importance of this species, N fertilizer sources, rates, and timing of application have not been thoroughly evaluated for this species. The object ive of this 3-yr study was to evaluate the effect of source, rate, and timi ng of applied N on Plains bluestem forage production. Two established stand s of Plains bluestem in Stillwater and Bessie, OK, were selected as experim ental sites. A randomized complete block design with three replications was employed at each location. Urea and ammonium nitrate were evaluated at rat es of 50, 100, 200, and 400 lb N/acre. Time of fertilizer application was e valuated using late April and early May applications. Dry matter yield, cru de protein (CP), and N uptake increased with applied N up to 200 Ib N/acre for both sources. The maximum average (3-yr) yields were 4112 and 3370 lb d ry matter/acre at Stillwater and Bessie, respectively. No effect on product ion was found to exist due to N source. Applying 50 and 100 Ib N/acre in ea rly May increased yields at Stillwater 25 and 14%, respectively, compared w ith the same rates applied in late April. This study indicated that Plains bluestem forage yield, N uptake, and CP content increased significantly whe n up to 200 Ib N/acre was applied in the spring. Dry matter production was further increased when N was applied in early May compared with late April.