Shading Effects on Marandu Palisadegrass in a Silvopastoral System: Plant Morphological and Physiological Responses

Abstract

The understanding of plant morphological and physiological responses to shading can contribute to developing sustainable silvopastoral systems (SPS). Our objective was to evaluate the shading effect on herbage accumulation (HA), plant‐part composition, physiology, and canopy structural characteristics of Marandu palisadegrass {Urochloa brizantha (Hochst. ex A. Rich.) R.D. Webster [syn. Brachiaria brizantha (Hochst. ex A. Rich.) Stapf]} under intermittent defoliation in a SPS with Eucalyptus urograndis (hybrid of Eucalyptus grandis W. Hill ex Maiden and Eucalyptus urophylla S.T. Blake) in Sinop, Mato Grosso, Brazil. The experimental design was a randomized complete block arranged under a strip‐split‐plot, where the plots were allocated to four distances from the Eucalyptus grove (3, 6, 10, and 15‐m) in the SPS, on both faces (north and south), with four replications. The evaluations were done during two summer rainy seasons (RS1 and RS2) and one dry season (DS). The herbage accumulation (HA) in RS1 (4290 kg DM ha–1) was 51% greater than in RS2. The greatest canopy height, light interception, and leaf area index (LAI) values were measured during RS1 (25 cm, 91%, and 3.5 cm2 cm–2, respectively). Leaf photosynthesis rate was less at the 3‐m distance (12.5 μmol CO2 m–2 s–1) than at other distances (17.3 μmol CO2 m–2 s–1). We conclude that Marandu palisadegrass has the ability to physiologically adapt to shaded environments, although the dynamics along the whole tree growing cycle needs to be considered so that grass productivity can be sustained in the long‐term.Core Ideas Longer shading impacted canopy structure and forage accumulation at 3‐m distance. Physiological responses shows reduced light effects on the forage growth pattern. Morphologic composition and sward characteristics were only affected at 3‐m distance. Leaf photosynthesis rate was lesser close to the grove. Silvopastoral systems is an option for livestock production in the Brazilian Amazon.