Bluestem Forage Yield Response to Source, Rate, and Timing of Applied N, and Spring Burning

Plains bluestem ( Bothriochloa ischaemum L.) is one of the primary grass species used for pastureland in Oklahoma. Plains bluestem is popular due to its high forage and beef production potential. It is also used for soil conservation on highly erodible areas. Despite the current importance of this species, N fertilizer sources, rates, and timing have not been thoroughly evaluated. The objective of this study was to evaluate the response of bluestem forage production as a function of source, rate, and timing of applied N and spring burning. Two established bluestem pastures in Stillwater and Bessie, Oklahoma, were selected as experimental sites. A randomized complete block design with three replications was employed at both locations. Urea and ammonium nitrate were evaluated at rates of 56, 112, 224, and 448 kg N ha . The effects of spring burning and time of application were also evaluated. Dry matter yield, protein, and N uptake response to applied N were linear up to 224 kg N ha -1 for both sources with the maximum average (3-yr) yields being 4.6 Mg ha -1 and 3.8 Mg ha -1 at Stillwater and Bessie, respectively. No significant effects on production were found to exist due to N source or burning. Forage yields increased when N was applied in May vs. April. Nitrogen use efficiency rates were greatest when 112 kg N ha -1 was applied in May (35.6% and 20% at Stillwater and Bessie, respectively). Economic analysis indicated that applying 112 kg N ha -1 in May resulted in net profits at both locations.