Silvopastoral systems integrate trees, pastures, and animals aiming for sustainable livestock production. The APSIM model has been used to simulate silvopastoral systems but the estimates of light transmission through the tree canopies, belowground water competition, and their effects on pasture production, have not been well adjusted. Thus, we improved the simulation of pasture growth within a silvopastoral system by integrating the APSIM-Tropical Pasture and APSIM-Slurps models and calibrated the coupled models to simulate light transmission through the trees along with water competition among species. Observed data was obtained from a silvopastoral system established in São Carlos, SP, Brazil, during two experimental periods that went from Dec-2014 until May-2016 and from Apr-2018 until May-2019. The calibration of the combination of the models was considered overall accurate. The APSIM-Slurp model simulated well (R² = 0.64, NSE = 0.60) the radiation interception by trees. The APSIM-Tropical Pasture model showed a good performance to simulate pasture (R² = 0.90 and NSE = 0.72), leaf (R² = 0.82 and NSE = 0.44), and stem (R² = 0.82 NSE = 0.75) biomass and an acceptable performance for pasture LAI (R² = 0.76 and NSE = 0.58). With that, a multifactorial simulation was performed to test the sensitivity of pasture production as a function of levels of nitrogen, tree leaf area index (LAI), tree root water extraction coefficient, post grazing residual biomass, and season of the year, using 39 years of weather data from the same location of the field experiment as input. The sensitivity analysis showed that the combination of the models was sensitive to variations of the factors with the greatest sensitivity occurring for the tree LAI. The assembling of APSIM-Tropical Pasture and APSIM-Slurp models well simulated pasture production in a silvopastoral system with different managements, indicating the potential of its use as a decision-making tool for silvopastoral systems´ design.

中文翻译：

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利用 APSIM 相关模型对热带林牧系统牧草生长进行模拟和敏感性分析


林牧系统将树木、牧场和动物融为一体，旨在实现可持续畜牧生产。 APSIM模型已用于模拟林牧系统，但对树冠光传输、地下水竞争及其对牧场生产影响的估计尚未得到很好的调整。因此，我们通过集成 APSIM-热带牧场和 APSIM-Slurps 模型改进了林牧系统内牧场生长的模拟，并校准了耦合模型以模拟通过树木的光传输以及物种之间的水分竞争。观测数据是从巴西圣卡洛斯建立的林牧系统中获得的，该系统在2014年12月至2016年5月和2018年4月至2019年5月的两个实验期内获得。模型组合的校准被认为总体上是准确的。 APSIM-Slurp 模型很好地模拟了树木对辐射的拦截（R² = 0.64，NSE = 0.60）。 APSIM-热带牧场模型在模拟牧场（R² = 0.90 和 NSE = 0.72）、叶子（R² = 0.82 和 NSE = 0.44）和茎（R² = 0.82 NSE = 0.75）生物量方面表现出良好的性能，并且在生物量方面表现出可接受的性能。牧场 LAI（R² = 0.76，NSE = 0.58）。由此，进行了多因素模拟，使用 39来自现场实验同一地点的多年天气数据作为输入。敏感性分析表明，模型组合对树 LAI 敏感性最大的因素的变化很敏感。 APSIM-Tropical Pasture 和 APSIM-Slurp 模型的组合很好地模拟了不同管理的林牧系统中的牧草生产，表明其作为林牧系统设计决策工具的潜力。