Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2004
Publication Date: 8/1/2005
Citation: Burner, D.M., Mackown, C.T. 2005. Herbage nitrogen recovery in a meadow and loblolly pine alley. Crop Science. 45(5):1817-1825. Interpretive Summary: The adoption of silvopasture technology has been limited in the US partly because of poor understanding of the competitive interactions between the three main products: wood fiber, grass, and livestock, and how production is affected by fertilization. Our objective was to determine whether grass in a meadow and pine alley differed in the use of fertilizer nitrogen for growth and quality. High nitrogen rates increased grass yield in the meadow, but also increased nitrate to levels in the pine alley to levels that might be harmful to livestock. Our finding that grass can use only low levels of fertilizer nitrogen in the pine alley is important because it addresses best management practices for economical, environmentally-friendly, sustainable silvopasture production.
Technical Abstract: Fertilizer management practices in agroforestry systems could be improved if the complex interaction of economic efficiency, herbage and livestock production, and tree growth were better understood. Our objective was to determine effects of N on herbage N use and nutritive value at two sites, a meadow without trees and a loblolly pine (Pinus taeda L.) alley (995 trees/ha). The test was conducted on a Leadville silt loam soil (fine-silty, siliceous, thermic Typic Fragiudult) near Booneville, Arkansas in 2002 and 2003. Tall fescue (Festuca arundinacea Schreb.) was the main herbage species at both sites. Fertilizer N was broadcast as split-applications at six rates (100 kg/ha increments from 0 to 500 kg/ha/yr). The proportion of total herbage as tall fescue was favored at rates > 200 kg N/ha, but these rates increased herbage nitrate-N in the pine alley to potentially harmful levels for grazing ruminants (>2300 ug nitrate-N/g). Cumulative herbage N use efficiency (NUE) in the meadow was nearly twice that in the pine alley, 23 and 10 kg dry weight per kg N supplied, respectively. The apparent increase in crude protein in pine alley vs. meadow herbage appeared to be a mechanistic response to decreased specific leaf weight. Only maintenance levels (< 100 kg/ha) of N fertilization should be applied to the pine alley given markedly lower herbage NUE than meadow herbage, and to minimize risk of nitrate-N toxicity to ruminant livestock when large amounts of fertilizer N are applied.