Relative effects of irrigation and intense shade on productivity of alley-cropped tall fescue herbage

摘要

The relative effects of irradiance and soil water on alley-cropped herbage are poorly understood. Our objective was to determine effects of irrigation on herbage productivity when tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] was grown in two sites, a meadow and a loblolly pine (Pinus taeda L.) alley (620 trees ha−1), near Booneville, Arkansas. Three tall fescue entries were space planted in the meadow and pine alley with or without irrigation. Herbage mass and nutritive value were determined at 8-week intervals for 2 years. Mean daily PAR was 33.9 (2004) and 37.5 mol m−2 d−1 (2005) in the meadow, while the pine alley received 5.6 mol m−2 d−1 (17% of the meadow) in 2004 and 4.3 mol m−2 d−1 (11% of meadow) in 2005. Effect of tall fescue entry tended to be small relative to site and irrigation. Irrigation compensated for evapotranspiration in the meadow, but not in the pine alley when summer rainfall was about normal (2004) or low (2005). Nevertheless, site (PAR) had a greater effect on herbage specific leaf weight, leaf elongation rate, tillers plant−1, mass tiller−1, and total nonstructural carbohydrate concentration than soil water. Irrigation might have had greater impact on herbage productivity if more water had been applied or if canopy cover had been less extreme. Silvicultural practices should be imposed to improve penetration of solar irradiance to the alley crop.