The objective of this research was to quantify leaf photosynthetic rates during the regrowth period and to model canopy photosynthesis of vegetative swards of Xaraés palisadegrass [Brachiaria brizantha (A. Rich.) Stapf.] under contrasting management strategies of rotational stocking. Early regrowth was characterized by low photosynthetic potential (10.4 µmol CO2 m-2 s-1) and for paddocks under the 100% LI treatment, leaf photosynthesis was 3.3 µmol CO2 m-2 s-1, which may require plants to draw on organic reserves during the early phases of the process. Half way through regrowth, leaf photosynthetic rates increased to 26 µmol CO2 m-2 s-1 in all treatments. Paddocks under the 95% LI treatment (shortest mean regrowth periods; 22 days), sustained pre-graze photosynthetic rates at 26.1 µmol CO2 m-2 s-1. The longer regrowth intervals (28 and 32 days on average, for the 28 d and for the 100% LI paddocks, respectively), resulted in lower rates of 21.3 and 24.5 µmol CO2 m-2 s-1, respectively. Under the highest grazing frequency (95% LI), the short rest period and the low mean LAI (2.08) allowed for more light penetration into the canopy. Optimum management practices for Xaraés palisadegrass should include grazing intervals shorter than 28 days, so that higher photosynthetic rates are achieved during the regrowth period.
canopy photosynthesis; carbon assimilation; leaf area index; light extinction coefficient
