基于不确定性的限量供水灌溉预报节水增产机制

Limited water supply for Irrigation ，which can not meet the crop water requirement sufficiently，is often found because of great interannual precipitation variability and water resources scarcity in arid and semiarid areas. According to the existing irrigation forecasting algorithms, the limited irrigation water will be moved forward and the serious shortage of water will be occurred during the late growth period, which will cause severe yield reduction as a result. The study focuses on the effect of water stress on crop growth including growth process, growth environment, morphology and yield by field experiment. Meanwhile, crop water model is established. Then appropriate indicator of irrigation thresholds is determined based on optimal irrigation schedule under different irrigation amount in typical years. The relationship between irrigation thresholds and its influencing factors is also explored in this study. Then an irrigation thresholds algorithm with multivariate such as crop growth time and teal-time water supply, etc. is proposed. Effect factors of water saving-yield increasing benefit such as soil moisture variation prediction method, forecast period, multi-source weather data, error of irrigation thresholds estimation and their uncertainty is analyzed by numerical simulation in order to reveal the mechanism of water saving-yield increasing benefit. An improved algorithm based on existed irrigation forecasting theory is established which can be applied in irrigation forecasting under limited water supply. This study can be applied either in sufficient irrigation forecasting or insufficient irrigation forecasting which will promote the application of irrigation forecasting and lead to scientific support and practical value in high-efficiency irrigation management.

干旱半干旱地区年际间降水量变化较大，加之水资源严重紧缺，限量供水灌溉现象非常普遍。限量供水条件下，使用现状灌溉预报方法，将使有限灌溉供水量前移，导致作物生长后期严重干旱减产。本项目拟通过控制性试验，研究干旱胁迫对作物生长过程、生长环境和最终产量的影响，改进作物水模型，确定作物优化灌溉制度，筛选适宜灌水下限指标，探索灌水下限影响因素及其之间的关系，由此建立多变量（如作物生长时间、实时灌溉供水和降水量等）灌水下限预测模型；采用数值模拟方法分析墒情预测方法、预见期、天气信息和灌水下限等因素及其不确定性对灌溉预报节水增产效益的影响，揭示灌溉预报的节水增产机制，改进和完善灌溉预报方法，使之适合于限量供水条件下的灌水决策。本研究成果可将限量供水条件下灌溉预报与充分供水灌溉预报有机地统一起来，促进灌溉预报技术的推广应用，进一步提高有限供水的利用效率，具有重要的理论与生产价值。

干旱半干旱区年际间降水量变化较大，水资源严重紧缺，普遍实施限量供水灌溉。探求合理确定灌水时间的方法，是提高有限水资源利用效率、保障灌溉农业稳产高产持续发展的重要措施。目前普遍采用经验法确定限量供水的灌溉时间，该灌水时间不随年份变化，与年度作物需水要求不匹配；若采用适宜灌水下限，会使有限灌溉水量前移，导致作物生长后期严重干旱减产。针对该问题本项目开展了田间试验和理论研究。田间试验获得了两个试点冬小麦复播玉米、春玉米和冬小麦系统的作物根、茎、叶和籽粒干物质重对水分养分胁迫的反应测试资料；收集了5个年度冬小麦复播玉米（1个试验站）和4个年度春玉米（1个试验站）大田灌水施肥对作物生长过程和产量影响的试验资料。理论研究是将土壤水、热、溶质（氮素、盐分等）动力学理论与PS123作物生长模型耦合，引入作物生长相关性和根系吸氮量模拟，构建作物水模型；基于作物蒸散量随供水量减小而减小的特性，构建了确定灌水时间的蒸散量法模型；选择若干典型年，以种植效益最大为目标函数，优化确定灌水时间，获得相邻两次灌水期间累计蒸散量和累计有效降水量，据此确定蒸散量法模型参数；利用近10年气象资料，分析蒸散量法（较经验法）的增产增收效果。结果表明，由于天气因素变化的不确定性，某一年的增产增收可能是负值，但是，多年平均而言，三种作物或模式均具有明显的增产增收效果。其中冬小麦最为明显，且以两次灌水效果最大，增产量达到8.9%，增加收益达27.3%；春玉米次之，增产可达6.9%，增加收益达24.1%；冬小麦复播玉米增产增收效果具有随可供灌水次数增加而增大的趋势，如灌水3次和4次增加收益分别为4.0%和5.4%。本研究提出的蒸散量法具有严密的理论基础，显著优于传统的灌水下限法和经验法，具有更宽的适用范围，不仅可用于限量供水灌溉预报，而且可用于充分供水灌溉预报。该方法是对作物灌溉理论的丰富和完善，有助于促进灌溉预报技术的推广应用，具有重要的理论与生产价值。