Crop production in the tropics and sub-tropics increasingly relies on phosphorus (P) fertilisers to maintain crop yields. As a result, there is a need to better understand the effectiveness of P management strategies, especially in Vertisols that represent a large proportion of the cropped area. The complexity of soil P dynamics and the interaction with environmental factors and farming practices make this challenging but the use of agricultural systems models such as the Agricultural Production Systems sIMulator (APSIM) can potentially improve our understanding of these interactions. This study (1) gives the state of knowledge of P behaviour in Vertisols and identifies which soil P processes are simulated in the APSIM Soil-P module, (2) tests the ability of APSIM as a tool to simulate soil P dynamics and crop responses in two long-term P studies in Vertisols, and (3) discusses future work needed to improve modelling of soil P dynamics. Soil P dynamics in Vertisols are not well understood, but evidence suggests that precipitation and dissolution of calcium-P minerals may play a significant role in plant P availability. These characteristics are substantially different to the strongly P-sorbing soils on which the APSIM model has previously been tested, so the ability of the model to simulate soil P dynamics and crop responses on these soils is untested. The APSIM model was able to predict the variation in crop yields due to seasonal variation of moisture availability within an acceptable modelling performance but was less able to predict P responses within seasons. This weakness was consistent with the lack of linear correlation between the plant-available P pools predicted by the P module and the measured Colwell-P that was correlated with crop responses. The non-linear relationships also differed between the two Vertisols. The poor understanding of P dynamics in Vertisols and the inability to partition soil P into measurable P pools is hindering the development of a mechanistic P module. The resulting lack of an appropriate mechanistic approach to soil P dynamics questions the predictive ability of the model. Further fundamental work is needed to predict the fate of applied P fertilisers in soils with contrasting physical and chemical characteristics, with this information integrated into an improved P modelling framework.

热带和亚热带的作物生产越来越依赖磷 (P) 肥料来维持作物产量。因此，需要更好地了解磷管理策略的有效性，尤其是在占种植面积很大比例的 Vertisols 中。土壤磷动态的复杂性以及与环境因素和农业实践的相互作用使这具有挑战性，但使用农业系统模型，如农业生产系统模拟器 (APSIM) 可以潜在地提高我们对这些相互作用的理解。本研究 (1) 提供了 Vertisols 中 P 行为的知识状态，并确定了 APSIM Soil-P 模块中模拟了哪些土壤 P 过程，(2) 在 Vertisols 的两项长期 P 研究中测试 APSIM 作为模拟土壤 P 动态和作物响应的工具的能力，以及 (3) 讨论改进土壤 P 动态建模所需的未来工作。Vertisols 中的土壤磷动态尚不清楚，但有证据表明钙磷矿物质的沉淀和溶解可能对植物磷的可用性起重要作用。这些特性与之前测试过 APSIM 模型的强吸磷土壤有很大不同，因此该模型模拟这些土壤上土壤磷动态和作物响应的能力未经测试。APSIM 模型能够在可接受的建模性能范围内预测由于水分可用性的季节性变化而导致的作物产量变化，但无法预测季节内的 P 响应。这种弱点与 P 模块预测的植物可用 P 库与与作物反应相关的测量 Colwell-P 之间缺乏线性相关性是一致的。两个 Vertisol 之间的非线性关系也不同。对 Vertisols 中 P 动力学的了解不足以及无法将土壤 P 划分为可测量的 P 池，这阻碍了机械 P 模块的发展。由此导致的土壤 P 动力学缺乏适当的机械方法对模型的预测能力提出了质疑。需要进一步的基础工作来预测在具有对比物理和化学特征的土壤中施用磷肥的命运，并将这些信息整合到改进的磷建模框架中。