Estudio de la heterogeneidad estructural del campo natural sometido a dos ofertas de forraje en pastoreo continuo y rotativo

The present work was carried out at the Mario A. Cassinoni Experimental Station of the Faculty of Agronomy - University of the Republic, located on National Route No. 3 Gral. José Gervasio Artigas, kilometer 363, in the department of Paysandú, Uruguay. The study was conducted on paddock 13 (Lat -32.387511°S and Long -58.033235°W), covering an area of 37,8 hectares of restored natural grassland, where an experiment with a factorial treatment structure (2x2) is set up to evaluate two grazing methods (Continuous and Rotational) and two forage allowance levels (High and Low, with the combinations being 12% in spring-summer and 8% in autumn-winter, and 8% in spring-summer and 4% in autumn-winter, respectively). The animals used are Holando steers in the rearing phase. The forage allowance levels are adjusted monthly according to forage availability (kg DM/ha) and the expected growth rate, regulating animal loads based on monthly weighing data. The evaluation period extended from March 15 to June 23, 2023, encompassing the autumn season. The objective of the study was to characterize the structural heterogeneity and botanical composition of the natural grassland subjected to different grazing managements, relating these factors to the individual animal response obtained. For a better interpretation of the results, the area was classified into three zones - Lowland, Mid-slope, and Lithosol - corresponding to contrasting soil types, according to cartography and visual field estimation. The variables determined were forage height (cm), forage mass present (kg DM/ha), botanical composition, and average daily gains of the animals (kg LW/d). For the analysis of the results, the statistical software InfoStat was used, applying multivariate and univariate descriptive techniques (ANOVA), and the test of homogeneity of variances (Levene's Test); subsequently performing mean comparison tests using Tukey's test with a significance level of 10%. The results showed that the pasture structure (height) was conditioned by the grazing method and the zone, more than by the forage allowance level; with greater heights in the Rotational method, and according to the zone, in both grazing methods, in descending order from Lowland, Mid-slope, and Lithosol. Structural heterogeneity was conditioned by the forage supply level, and secondly, by the studied zone; with greater heterogeneity at High forage allowance levels, and in the same descending order from Lowland, Mid-slope, and Lithosol. The botanical composition was primarily defined by the studied zone, with independent responses according to the grazing method and forage allowance level; observing contrasting sets in vegetative and productive types, according to these latter two factors. The average daily gains of the animals did not show significant differences according to the applied treatments.