CONTEXT

Silvopastoral systems aim to be more sustainable than conventional systems, increasing total productivity, diversifying agricultural production, and improving resource use efficiency. However, very few studies were performed to adapt crop models to simulate these systems.

OBJECTIVE

This study investigates the current capacity of the APSIM Next Generation model to estimate Piatã palisadegrass growth and soil water in different positions in a silvopastoral system with eucalyptus by looking at the impact of modelling belowground and aboveground competition separately.

METHODS

A field experiment was conducted from December 2014 to January 2016 in a silvopastoral system with eucalyptus trees arranged in single rows, in East-West orientation, with 15 m between rows and 2 m between trees in the rows. This experiment was conducted under grazing management and rainfed conditions, during 11 growth cycles, with pasture variables, soil moisture and microclimatic conditions assessed at four distances from the eucalyptus north row (0.00 m, 3.75 m, 7.50 m and 11.25 m). APSIM testing was performed in two ways: focusing on belowground competition for soil water and nitrogen, using a multi-root-zone approach, and focusing on competition for solar radiation, using the measured data of solar radiation at each position.

RESULTS AND CONCLUSIONS

The APSIM-Tropical Pasture model was effective in simulating pasture growth when only competition for solar radiation was considered (R² from 0.75 to 0.86, Agreement index (d) from 0.88 to 0.96, and Nash-Sutcliffe efficiency (NSE) between 0.32 and 0.85). These simulations are promising taking into account the difficulties to simulate pasture growth in silvopastoral systems with grazing; however, in systems with strong belowground competition for soil water and nutrients, this approach has strong limitations. Simulations of pasture growth were not as effective when using the multi-root-zone approach (R² between 0.57 and 0.87, d between 0.53 and 0.74, and NSE from −5.32 to −1.20), despite reasonable simulations of soil water for the positions between the tree rows (R² between 0.70 and 0.80, d from 0.91 to 0.94, and NSE between 0.60 and 0.77). In view of these results, improvements should be performed in APSIM to better simulate silvopastoral systems, mainly for solar radiation transmission and tree roots growth and distribution.

SIGNIFICANCE

This study allowed identifying the key drivers of competition within the studied environment and to inform where the main efforts should be targeted in building a more effective model for silvopastoral systems. This is important to help model development teams in organising and optimising their efforts.

中文翻译：

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APSIM模型在模拟桉树林牧系统不同位置的Piatã栅栏草生长和土壤水分的性能

语境

林牧系统旨在比传统系统更具可持续性，提高总生产力，使农业生产多样化，并提高资源利用效率。然而，很少有研究采用作物模型来模拟这些系统。

客观的

本研究通过分别观察地下和地上竞争建模的影响，调查了 APSIM Next Generation 模型在估计具有桉树的林牧系统中不同位置的 Piatã palisadegrass 生长和土壤水分的当前能力。

方法

2014年12月至2016年1月在林牧系统中进行了田间试验，桉树单行排列，东西向，行距15 m，行距2 m。该试验在放牧管理和雨育条件下进行，在 11 个生长周期内进行，在距桉树北行的四个距离（0.00 m、3.75 m、7.50 m 和 11.25 m）评估牧场变量、土壤湿度和小气候条件。APSIM 测试通过两种方式进行：关注土壤水和氮的地下竞争，使用多根区方法，以及关注太阳辐射的竞争，使用每个位置的太阳辐射测量数据。

结果和结论

当仅考虑太阳辐射竞争时，APSIM-Tropical Pasture 模型可有效模拟牧场生长（R ²从 0.75 到 0.86，一致性指数 (d) 从 0.88 到 0.96，纳什-萨特克利夫效率 (NSE) 在 0.32 到 0.85 之间） ）。考虑到在放牧的林牧系统中模拟牧草生长的困难，这些模拟是有希望的；然而，在对土壤水和养分有强烈地下竞争的系统中，这种方法有很大的局限性。使用多根区方法（R ²介于 0.57 和 0.87 之间，d 介于 0.53 和 0.74 之间，NSE 介于 -5.32 到 -1.20 之间）时，牧场生长的模拟并不那么有效，尽管对这些位置的土壤水进行了合理的模拟树行之间 (R ²0.70 至 0.80 之间，d 0.91 至 0.94，NSE 0.60 至 0.77）。鉴于这些结果，应在 APSIM 中进行改进，以更好地模拟林牧系统，主要针对太阳辐射传输和树根生长和分布。

意义

通过这项研究，可以确定所研究环境中竞争的关键驱动因素，并告知在建立更有效的林牧系统模型方面应重点努力的目标。这对于帮助模型开发团队组织和优化他们的工作很重要。