Herbage nitrogen recovery in a meadow and loblolly pine alley

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 ha(-1) increments from 0 to 500 kg ha(-1) yr(-1)). 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 (less than or equal to 6 microgram g(-1)), 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 ha(-1)) in pine alleys fertilized with greater than or equal to 200 kg N ha(-1) yr(-1), only maintenance levels of fertilizer N (less than or equal to 100 kg ha(-1)) should be applied to similar sites. For these same reasons, yearly applications of fertilizer N > 300 kg ha(-1) yr(-1) are not recommended for meadows similar to the study site.