Can pasture defoliation management targets be similar under full sun and shaded conditions?

Abstract

Context ​Defoliation management targets applied to forages under the full sun have not yet been properly evaluated for shaded environments such as occur in integrated crop–livestock systems with the presence of trees. Aims This study aimed to determine defoliation targets under full sun and shaded environments for the shade-tolerant perennial summer grass hybrid Axonopus catharinensis (giant missionary grass), widely used in pasture systems of South Brazil and Argentina. Methods Four pre-defoliation canopy heights (15, 25, 35 and 45 cm) and four defoliation severities (20%, 40%, 60% and 80% reduction in pre-defoliation canopy height) were evaluated. Plants were grown in 0.15 m3 wooden boxes filled with sand/vermiculite substrate (1:1 v/v) and irrigated with a complete nutrient solution. An artificial shade structure was made with wooden slats, reducing light intensity by 50% for shaded plants. Key results Herbage accumulation decreased by 54% in shaded plants compared with those under full sun. Regardless of the light environment, the lowest crude protein content (<150 g/kg dry matter) and the highest neutral detergent fibre content (>650 g/kg dry matter) were observed when the defoliation target height was >35 cm. Both shaded and full sun environments showed decreases in tiller density when defoliation severity was >60% of pre-defoliation canopy heights. Conclusions Pre-defoliation canopy heights >35 cm and defoliation severity >60% of pre-defoliation canopy height should be avoided when managing A. catharinensis, regardless of the light environment. Implications Recommended targets may be easily implemented by livestock producers and are similar for full sun and shade environments.