Impact of tree integration in crop–livestock systems with varying nitrogen rates

Context The incorporation of trees into integrated crop–livestock systems (ICLS) has been encouraged because of their role in climate change mitigation through plant and soil carbon sequestration. One challenge is to minimize competition (especially for light) and the damage caused by cattle to trees. Aim This study sought to evaluate the performance of beef heifers grazing on cool-season grasses in two ICLS, crop–livestock (CL) and crop–livestock with immature Eucalyptus grandis trees (CLT), at two nitrogen (N) rates (50 and 150 kg/ha) on pasture. Because these were the first stocking seasons after tree planting, the physical impact of animals (e.g. debarking) on the trees was also evaluated. Methods The experimental design was randomized blocks with treatments arranged in a 2 × 2 factorial scheme (2 systems × 2 N fertilization rates), with three replicates. Forage production (as dry matter, DM) and animal performance were evaluated for 2 years. Key results Total forage production and liveweight (LW) gain per area over 117 days of grazing were on average higher for CL (6736 ± 565 kg DM/ha and 505 ± 58.6 kg LW/ha respectively) than for CLT (5455 ± 372 kg DM/ha and 364 ± 42.3 kg LW/ha), regardless of N rate, and even at similar sward heights (~24 cm). The damage caused by heifers to the bark of the trees was classified as high intensity in 91.1% of the trees, even after the trees had reached a diameter at breast height of 9.9 cm. Conclusions The interaction between livestock and trees was detrimental to the system’s productivity, affecting pasture growth, animal performance and the quality of trees as sawn wood. This finding underscores the importance of selecting appropriate tree species, plant density and species arrangement in ICLS. Implications Lower tree densities (<237 trees/ha) and preventive measures regarding the use of E. grandis in CLT systems with cool-season grasses are necessary in subtropical regions.