Shade and nitrogen fertilization affect forage accumulation and nutritive value of C4 grasses differing in growth habit

Light reduction in silvopastoral systems and self-shading in treeless grasslands can lead to shade-avoidance responses by tropical grasses. Light environment in association with nitrogen (N) supply influence the growth and nutritive value of forage grasses. This study aimed to quantify forage accumulation (FA) and forage nutritive value of tropical grasses differing in growth habit in environments with contrasting light and N resources. A field study was conducted using 'Jiggs' bermudagrass [Cynodon dactylon (L.) Pers.] and 'Mulato II' hybrid brachiariagrass (Urochloa spp). Full-sun environments were compared with shaded environments where shade cloth limited incident radiation to 45% of ambient. Low and high N treatments were imposed (30 and 120 kg N ha(-1) after each harvest), resulting in a 2 x 2 x 2 factorial arrangement of treatments in four replicates of a randomized complete block design. Forage was harvested every 28 d from May to September in 2014 and 2015 to determine FA. Herbage crude protein (CP) concentration and in vitro digestible organic matter (IVDOM) were assessed. Annual FA was greater for Mulato II than Jiggs and for high-N and full-sun treatments. Species showed similar CP concentrations, but Mulato II had greater IVDOM than Jiggs, likely due to a greater leaf percentage. Shade increased CP concentration of the forages whereas effects on IVDOM were not consistent. Although more productive with greater leaf percentage and nutritive value than decumbent, stoloniferous Jiggs, upright-growing, bunchgrass Mulato II was not persistent when multiple freeze events occurred during winter, limiting its adoption in cooler subtropical environments.