Sward structure and herbage intake of Brachiaria brizantha cv. Piata in a crop-livestock-forestry integration area

摘要

Forage species tolerate varying degrees of shading. In agrosilvopastoral systems, forage plants are able to adjust and partially compensate growth reduction under light stress. These adjustments change morphological proportions and composition along the vertical profile of the sward. Sward morphological composition is directly related to animal intake behavior and performance. One objective of this study was to evaluate the effects of different tree shading levels on sward vertical structure of Piata palisadegrass cultivated in a crop-livestock forestry integration area. Another objective was to identify the relationship between sward vertical structure and herbage intake by cattle (Boss pp.). Three experiments were conducted simultaneously to evaluate three shading levels: 1. Full sunlight (FS); 2. Moderate shade (MS; 338 trees.ha(-1)); and Intense shade (IS; 714 trees.ha(-1)). Evaluation was performed during three periods in which total rainfall during the experimental period corresponded to 86, 12 and 2% (periods 1, 2 and 3, respectively). Pastures were rotationally stocked and grazed at 95% canopy light interception (LI) during regrowth (95% LI). Two strategies for taking the reference readings of LI were tested in IS paddocks: LI reading inside (under the tree canopy) and outside (under full natural light) the experimental area. The IS had greatest forage height and proportion of stems, both pre- grazing and post-grazing. Consequently, animals under IS had decreased bite mass and intake rate, pre- and post-grazing except for period 3. There was an effect of shading level on herbage crude protein (CP) concentration. Greatest CP concentrations were observed on IS areas. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) did not vary with shading levels. Herbage dry matter digestibility varied with evaluation period, and lowest values were recorded during period 3. Greater herbage intake was observed on FS and MS relative to IS, due to greater leaf proportion in sward herbage mass. Moderate shading is not so detrimental to system's productivity, highlighting the importance of adequate choice of tree species, plant density and arrangement.