Performance of Purunã beef heifers and pasture productivity in a long-term integrated crop-livestock system: the effect of trees and nitrogen fertilization

The incorporation of trees in integrated crop-livestock systems (ICLS) has been suggested to recovery degraded pastures and to improve production and environmental outcomes in livestock systems. A challenge for their long-term productive stability is to minimize competition (especially for light) among components of the systems. The objective of this study was to evaluate the performance of beef heifers grazing cool-season grasses in two different ICLS, crop-livestock only and crop-livestock with trees (CLT), and at two N supply levels (90 and 180 kg N ha −1 ), in the subtropical region of Brazil. This study was performed over two consecutive years (2017 and 2018), in 11–12-year-old tree plantation (238 trees ha −1 ) and after a drastic reduction in tree density (remaining ~ 40 eucalyptus trees ha −1 ). The experimental design was randomized blocks with treatments set up in split plots with three replications. Main plots were treatments (ICLS * N) and subplots were years. The results indicate that the moderate shading level (~ 36%) provided by trees in the CLT system affected pasture growth (the total herbage accumulation was reduced in 2.02 Mg ha −1 ), the daily gain per animal (− 27%) and, consequently, decreased carrying capacity (− 28%) and weight gain per area (− 42%). An increase in N availability was not enough to overcome these differences. The possible influence of previous periods with intense shading (> 50%) in this long-term experiment on the current results, via reduction in the quantity of residues (plant and animal) deposited on soil surface, is discussed, as well as possible strategies to reduce losses in animal production in CLT systems.