Grazing Intensity and Nitrogen Fertilization to Manage Invasive Kleberg Bluestem on Pangolagrass Pastures in Northern Mexico

Abstract

This study was conducted at the Aldama Experimental Station of the National Research Institute of Forestry, Crops, and Livestock in Aldama, Tamaulipas, Mexico. The objective was to determine the effect of grazing intensity (I) and nitrogen fertilization (F) on botanical composition and forage accumulation (FA) of a pangolagrass (Digitaria decumbens Stent.) (P) pasture with Kleberg bluestem (Dichanthium annulatum Forsk.) (D). Treatments evaluated resulted from the combinations of two levels of I (High= 80% and Medium= 50% utilization), and two levels of F (0 and 45 lb acre-1 of nitrogen). Response variables were seasonal and annual FA and percentage aerial canopy cover of D and P. Response variables were analyzed in complete randomized block design with a 2x2 factorial arrangement of treatments replicated twice. A selected set of orthogonal linear contrast comparisons was made to quantify differences attributable to grazing intensity and fertilization. Each single degree of freedom was tested for significance with the Student’s t-test. Differences were considered significant at the 0.05 level. Percentage of D and P varied inversely, and statistical difference was found only for F, D decrease averaged 39% in treatments with F. Forage accumulation was similar during the dry season. A significant (P<0.03) interaction between I and F was found for FA in the rainy season. The best results were obtained in the treatment of moderate grazing intensity and fertilization with a forage accumulation of 7213 lb ac-1 year-1 with 30% D aerial canopy cover compared to the treatment of high grazing intensity without fertilization which had a FA of 4086 lb ac-1 year-1 with 55% D.