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a USDA-ARS, Dale Bumpers Small Farms Research Center, 6883 South State Highway 23, Booneville, AR 72927
b USDA-ARS Grazinglands Research Lab., 7202 W. Cheyenne St., El Reno, OK 73036
* Corresponding author (E-mail: dburner{at}spa.ars.usda.gov)
Herbage in conventional pasture and agroforestry systems is managed for microclimate and spatial differences inherent to these systems, but managers have scarce data on which to base their decisions. Our objective was to measure herbage N fertilizer recovery at two sites, an unshaded meadow and a shaded alley in 10-yr-old loblolly pine (Pinus taeda L.). The test was conducted on a Leadvale silt loam soil (fine-silty, siliceous, semiactive, thermic Typic Fragiudult) near Booneville, AR, in 2002 and 2003, with tall fescue (Festuca arundinacea Schreb.) the predominant herbage species. Fertilizer N was broadcast as split-applications at six rates (100 kg ha1 increments from 0 to 500 kg ha1 yr1). The meadow and pine alleys had sufficient herbage yield for rotational livestock production. Cumulative herbage yield (CHY) in the meadow was much more responsive to added N than pine alley herbage, but average cumulative fertilizer N (CFN) recoveries were only 38% and 12%, respectively. A shallow fragipan, low available soil P (
6 µg g1), depletion of soil water in July to September (both sites), and low solar irradiance (pine alley) were likely contributors to low fertilizer N recovery and herbage productivity. Because of poor herbage yield response and substantial accumulation of soil mineral N (62 to 237 kg ha1) in pine alleys fertilized with
200 kg N ha1 yr1, only maintenance levels of fertilizer N (
100 kg ha1) should be applied to similar sites. For these same reasons, yearly applications of fertilizer N > 300 kg ha1 yr1 are not recommended for meadows similar to the study site.
Abbreviations: CFN, cumulative fertilizer N CHY, cumulative herbage yield CMN, cumulative net mineralized soil N CNY, cumulative N yield PAR, photosynthetically active radiation
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