Grazing Management For Improved Guinea Grass Persistence

Sustainable, tropical forage-livestock production systems must be based on maintenance of pasture botanical composition. Sheep were allowed to graze rotationally (14 d graze, 28 d rest) on a guinea grass (Panicum maximum) pasture at four levels of hcrbage-on-ofier (HO) of 4, 7, 10, and 13% dry matter of animal body weight (BW). Rotational grazing was continued for three years and HO was regressed on forage and animal data to determine carrying capacity of the pasture, Mean, yearly stocking rate declined linearly from 775 to 540 kg BW ha'1 d"1 in response to increasing HO. Grass canopy heights for the pre-graze (0,35-0,65 m) and post-graze (0,20-0.45 m) pasture increased in a curvilinear pattern with HO. In both eases, the greatest increase in height occurred between the 4% and 7% HO, followed by marginal increments as HO was increased further. Pre-graze herbage mass increased linearly from 1.0 to 2,5 Mg ha"1 and post-graze herbage mass increased curvilinearly from 0.7 to 2.0 Mg ha'1 as HO was increased. The guinea grass frequency of occurrence on pasture prior to initiation of grazing was approximately 95%. Frequency remained unchanged during tlte first year of grazing but declined to 75% following three years of rotational grazing at the 4% HO compared to 85-95% at the remaining HO. The frequency of broad leaf weed occurrence which was 17%, initially, remained constant under 13% HO treatment but increased linearly to approximately 100% as HO was reduced to 4%. Sheep average daily gain ranged between 0.071 and 0,076 kg independently of HO, whereas, due to major differences in stocking rates, yearly livewcight gain increased from 630 kg ha"1 with 13%, HO to 815 kg lia'1 with 4% HO treatments. These results indicate a direct link between high, short-term animal production potential at high stocking rates and rapid guinea grass pasture deterioration to undesirable plant associations. Our estimate of tlie optimum stocking rate under a rotational grazing management system for St, Croix ranged from 575 to 690 kg BW ha"1 da"\ depending on tlie seasonal rainfall (1000-1200 mm).