EFFECT OF STOCKING RATE ON SOIL PROPERTIES AND VEGETATION IN A NATIVE PASTURE OF THE HUMID TROPIC OF VERACRUZ, MEXICO

Abstract

The effect of stocking rate (SR: 2, 3 and 4 cows/ha) upon some soil and vegetation variables was evaluated in native pastures, during two periods: Sep/2005-Aug/2006 and Sep/2006-Aug/2007, covering the three climatic seasons: Rainy, northern-wind and dry, in Tlapacoyan, Veracruz. The botanical composition of the pasture was dominated by native grasses (Paspalum spp y Axonopus spp). Each pasture paddock received 3 days of grazing per 27 days of recovering. Measurements were done in two grazing cycles per season in two paddocks (replications) out of 10 available for grazing in each SR. The standing dry matter was similar (P>0.05) between stocking rates: 5380±243 kg/ha; but the contribution (%) of native grasses to the botanical composition was different (P<0.0001) between stocking rates: 69.4±2.2; 82.6±1.4 y 87.2±1.5 in the above order. Root length and density at 0-10 cm and 10-20 cm depths were not affected by the model effects; root density was not affected (P>0.05) by depth, but length was (P<0.05; 0-10: 37.9 ± 2.0; 10-20: 17.1 ± 1.2 mm/cm3). The soil apparent density was not affected by stocking rate. The proportion of bare soil was significantly (P<0.05) higher in 4 cows/ha than in 2 and 3 cows/ha. Nitrogen mineralization rate was affected (P<0.05) only by soil depth. Most response variables were not affected consistently by stocking rate. However, native grasses increased in the pasture as stocking rate increased and this did not bear any relationship to other measured variables.