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The objective of this study was to evaluate the structural and floristic composition performance of 19 accessions of Urochloa brizantha, associated with Stylosanthes guianensis CIAT-184 on an acid soil, after three years of simulated grazing. The variables live shoots-dead shoots ratio and floristic composition were analyzed. The measurements were made in all the rotations during the experimental period. The substitution of dead shoots was favorable in most of the treatments; four accessions stood out (CIAT-16322, CIAT-26646, CIAT-16332 and CIAT-16335) in which, at the end of the period, the index of substitution of dead shoots was over two. From the accessions, 36,6% reached a percentage higher than 80% at the end of the experimental period; the accessions CIAT-16317, CIAT-16335 and CIAT-16332 were the ones with higher presence of the base pasture (> 90%). In all the associations the legume was represented in a low percentage (< 16%); while the weeds remained, in most cases, below 20%. In general, the evaluated U. brizantha accessions showed an acceptable persistence or stability in time, and CIAT-16322, CIAT-26646, CIAT-16332 and CIAT-16335 stood out. [ABSTRACT FROM AUTHOR]

A collection of 19 Urochloa brizantha accessions was studied, in association with Stylosanthes guianensis on a soil characterized by acidity, in order to select the best ones for this soil type. The measured and estimated variables were: vegetative height, availability and non-consumed pasture residue. In addition, leafiness, cover, vigor, CP content, fiber (NDF and ADF) degradation and IVDMD, were determined. The interpretation of the results was done through principal component analysis; and for grouping the associations and selecting those that had similar characteristics, cluster analysis was used. The existence of a high accumulated variability (75,9%) was detected in the first four components. When analyzing the agronomic and nutritional value performance, after three years of exploitation, the formation of six groups was identified; the associations in which the accessions that form group II were present (CIAT-16335 and CIAT-26646) stood out, reaching the highest values in height, availability and utilization, as well as high vigor and high CP contents and IVDMD. These associations that included the accessions that belonged to group II (CIAT-16335 and CIAT-26646) were present showed the best performance, when making an overall analysis of agronomic and nutritional value variables. It is recommended to study structural and floristic composition variables, as well as the seed production potential, in order to propose a pre-commercial variety for the agroecosystems with acid soil. [ABSTRACT FROM AUTHOR]