撒施化肥下畦灌地表-土壤水肥耦合模拟方法研究

Inappropriate management of border irrigation with conventional fertilization is one of the major sources that induce the agricultural non-point source pollution. However there is still lack of relevant technical support for the evaluation, design and management of border irrigation now. This project will firstly construct the soil water-fertilizer transport model based on the unstructured cell which is suitable for conventional fertilization. Then by means of precisely distinguishing the mass and momentum conservation coupling of water-fertilizer between the surface and subsurface, the coupled method of water-fertilizer transport with high accuracy and efficiency between the surface and subsurface will be proposed. At the same time, the coupled surface-subsurface transport model of water-fertilizer for border irrigation with conventional fertilization will be developed. Based on the observed data, the simulation effect of the developed coupled model will be validated. Then the coupled model will used to analyze the impact of technical factors to the performance of border irrigation with conventional fertilization and provide the optimized combination of technical factors under different performance indicator values. This study can provide technical support and scientific basis for the evaluation, design and management of border irrigation system with conventional fertilization. And this study has important theoretical significance and practical value for improving conventional fertilization manner and reducing the agricultural non-point source pollution induced by the inappropriate border irrigation management with conventional fertilization.

不适宜的畦灌施肥管理是引起我国农业面源污染的主要途径之一，然而目前畦灌施肥系统的评价、设计和管理仍然缺乏相应的技术支撑。本项目拟在以往撒施畦灌地表水肥模拟研究成果的基础上，基于二维非结构空间单元格构建适用于撒施化肥下的畦灌土壤水肥模拟模型。基于此，通过精确区分地表与土壤水肥之间的质量与动量守恒耦合过程，提出具备高精度和效率的畦灌地表-土壤水肥输运扩散耦合方法，构建撒施化肥下畦灌地表-土壤水肥耦合输运扩散模拟模型。基于田间实测数据验证耦合模型的模拟效果，分析探讨不同畦灌施肥技术要素对畦灌撒施施肥系统性能的影响，提出不同畦灌施肥性能评价指标值下各撒施畦灌施肥技术要素的最优组合方案。本研究可为畦灌撒施施肥系统的评价、优化设计和管理提供技术支撑和科学依据，对于改进传统畦灌撒施施肥方式、减轻施肥不当引起的农业面源污染等问题具有重要的理论意义与实用价值。

本项目首先建立了全水动力学畦灌方程的全隐式标量耗散有限体积法。借助该解法，通过全隐式求解土壤水动力学方程和地表/土壤溶质对流-弥散/扩散方程，实现了撒施施肥方式下畦灌地表水流的对流与扩散、地表溶质的对流与弥散、土壤水在土水势梯度下的扩散以及土壤溶质的对流与扩散等七个物理过程的完全耦合。与以往已有解法相比，基于实测数据的验证结果表明，新建立的撒施施肥方式下地表-土壤水流与溶质运动全耦合模型具备无条件稳定的高效率，并保持高模拟精度。采用该模型系统探讨了不同撒施非均匀系数下畦灌施肥技术要素的最佳组合。最佳撒施非均匀系数USN下，小、中、大流量下畦面微地形需满足Sd ≤3.6、4.0cm、4.5cm时，不同畦长和土壤质地组合的施氮分布均匀性和施氮储存率可满足UCCN ≥75%、 EN≥ 75%。因此，针对畦长、土壤质地和入畦单宽流量等实际情况，提高畦面平整度，选择适宜的撒施非均匀系数，能够显著提高撒施下畦灌施肥性能，改善作物田间水氮条件。