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.

中文翻译：

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Purunã 小母牛的性能和牧场生产力在长期综合作物畜牧系统中：树木和施氮肥的影响

已建议将树木纳入综合作物畜牧系统 (ICLS) 以恢复退化的牧场并改善畜牧系统的生产和环境结果。它们的长期生产稳定性面临的一个挑战是最大限度地减少系统组件之间的竞争（尤其是对光的竞争）。本研究的目的是评估在两种不同的 ICLS，仅作物-牲畜和带树的作物-牲畜 (CLT) 以及两种 N 供应水平（90 和 180 kg N ha −1 )，在巴西亚热带地区。该研究连续两年（2017 年和 2018 年）在 11-12 年树龄的人工林（238 棵树 ha -1 ）和树木密度急剧减少（剩余约 40 棵桉树 ha -1 ）后进行。实验设计是随机区组，处理设置在三个重复的裂区中。主地块是处理（ICLS * N），子地块是年。结果表明，CLT 系统中树木提供的中等遮荫水平 (~ 36%) 影响了牧草生长（草本总积累量减少了 2.02 Mg ha -1 ）、每头动物的日增重 (- 27%) 和，因此，承载能力下降 (- 28%) 和单位面积重量增加 (- 42%)。N 可用性的增加不足以克服这些差异。通过减少沉积在土壤表面的残留物（植物和动物）的数量，讨论了在这个长期实验中以前的强烈阴影（> 50%）对当前结果的可能影响，