FORAGE PRODUCTION AND QUALITY OF 4 PERENNIAL GRASSES GROWN UNDER AND OUTSIDE CANOPIES OF MATURE PROSOPIS-GLANDULOSA TORR VAR GLANDULOSA (MESQUITE)

Comparisons were made of dry matter production and forage quality of two cool-season grasses, Canada wildrye (Elymus canadensis L.), Virginia wildrye (Elymus virginicus L.), and two warm-season grasses, green panic (Panicum maximum var. trichoglume Eyles) and plains bristlegrass (Setaria leucopila Scribn. & Merr.), planted under and outside the canopies of mature honey mesquite (Prosopis glandulosa Torr. var. glandulosa). Green panic gave the greatest cumulative dry matter yield in both canopy (5120 kg ha-1) and open (3370 kg ha-1) locations, followed by plains bristlegrass under mesquite (1130 kg ha-1) and in the open (570 kg ha-1). One-time yields from Canada wildrye and Virginia wildrye, under and outside mesquite canopy, were 247 and 329 kg ha-1, and 272 and 268 kg ha-1, respectively. Dry matter production of green panic (p = 0.001) and plains bristlegrass (p = 0.026) was greater under mesquite only for the first of four harvests, although both warm-season grasses exhibited a trend for greater production under mesquite than in the open. Average nitrogen content of green panic was greater (p = 0.0004) under mesquite than in the open, while plains bristlegrass exhibited a trend for greater crude protein content in the open than under mesquite. Overall, moisture content of the warm-season grasses was greater (p - 0.0001) under mesquite than in the open, while Virginia wildrye was more (p = 0.002) succulent under mesquite than in the open. Average in-vitro dry matter digestibility of warm-season grasses was almost significantly greater (p = 0.0501) in the open than under mesquite. Canopy soils contained significantly more organic C (p = 0.0004) and total N (p = 0.0001) than open soils, with differences of 8.3 Mg organic C ha-1 and 1.3 Mg total N ha-1. Correlations indicated that soil fertility was more limiting to grass production than light intensity.