Canopy Characteristics of Continuously Stocked Limpograss Swards Grazed to Different Heights

Abstract

Vertical heterogeneity in herbage bulk density, plant‐part proportion, and nutritive value is common in canopies of C4 grasses. Changes from top to bottom of the canopy affect performance of cattle (Bos ssp.) grazing limpograss [Hemarthria altissima (Poir.) Stapf & Hubb.], but this variation has not been described under continuous stocking. During 1998 and 1999 the effect of grazing height (20, 40, and 60 cm) on limpograss herbage characteristics was assessed in three canopy layers (top 5 cm, upper 25% by height, and next lower 50% by height). Total and leaf bulk density decreased with increasing height for all layers. Averaged across years and layers, total bulk density was 137, 80, and 63 kg ha−1 cm−1 for 20‐, 40‐, and 60‐cm canopies, respectively. Leaf percentage was greater in the upper 25% (19%) than next lower 50% of the canopy (11%). Leaf and stem crude protein (CP) and in vitro organic matter digestibility (IVOMD) decreased from the upper 25% to next lower 50% of the canopy (129 to 123 g kg−1 for leaf CP, and from 50 to 40 g kg−1 for stem) and with increasing sward height, but leaf and stem fractions differed much less proportionately in IVOMD than CP. Results support the hypothesis that canopy height is an important factor affecting canopy characteristics of continuously stocked limpograss pastures. Pastures grazed to the intermediate 40‐cm height appeared to give the best combination of lower bulk density, associated with greater opportunity for leaf selection, plus relatively high nutritive value.