干湿胀缩下农田土壤裂隙对微润灌的水肥驱动效应及控制

Moistube irrigation, driven by the hydraulic potential difference between working pressure head inside the moistube and matric potential in soils outside the moistube, accurately and continuously transfers water to root zones. While, the existence of soil desiccation cracks and gaps tend to induce fingering flow and deep percolation in moistube irrigation. This proposal aims (1) to reveal the cumulative effects of shrink-swell cycles on crack morphology, water conductivity characteristics, water retention Cumulative effect of fissure and soil repellency after the soil undergoes repeated WD cycles under moistube irrigation; (2) to observe the patterns of infiltrating body and to figure out how the solute accumulates and transports in the cracked soils undergoing WD cycles under moistube irrigation; (3) to numerically simulate the water movement and solute transport under moistube irrigation, based on the mechanism of crack closing process; (4) to analyze the effects of cracks on capillary rupture, the water storage ratio in root zones, irrigation uniformity and deep percolation, to evaluate the effects of cracks on water use efficiency and to put forward optimal control schedule of moistube irrigation. The research findings favor comprehensively revealing the mechanisms of water movement and solute transport in shrink-swell soils with cracks under moistube irrigation, and provides fundamental basis for promoting irrigation-fertilizing efficiency.

微润灌以管内水头和管外基质势差为驱动力，连续、精量地向根区提供水分，然而农田土壤干缩裂隙易造成指流和深层渗漏等现象。该项目旨在（1）揭示微润灌干湿循环下裂隙累积效应，以及土壤导水特征、持水特征和可溶性肥施用后土壤亲斥水特性的变化；（2）结合室内断层扫描和大田染色示踪试验，探求多重干湿胀缩下裂隙及管壁空隙对微润灌浸润体发育和溶质积累、迁移的影响；（3）构建裂隙干湿胀缩影响下的微润灌水分、溶质迁移模拟模型；（4）分析裂隙造成的毛管断裂效应，田间根系层储水率、灌水均匀度和深层渗漏等指标，评价裂隙对微润灌水肥利用的影响，构建干湿胀缩下微润灌最优控制模式。研究成果将揭示微润灌在土壤干湿胀缩裂隙影响下的水分、养分运移机理，为提高微润灌水肥利用效率提供理论依据。

微润灌在管内外水势差作用下，将水肥从纳米孔精准输送至作物根区；农田存在干缩裂隙，其改变水肥运移路径，影响微润灌节水保肥功能。项目对土壤缩胀理论、裂隙发育和微润灌水肥运移规律展开了研究，揭示了微润灌水肥一体化条件下裂隙变化及其对水肥迁移影响规律，构建了裂隙发育离散元模型和基于水势差驱动机制的微润灌水分运移模型，提出了微润灌溉系统技术参数。成果如下：.（1）土壤收缩随循环级数推进而减弱，无机肥添加显著减小比例收缩阶段从而抑制土壤收缩，VG-Peng模型拟合收缩特征效果良好，土壤收缩经历纵向收缩-以纵向收缩为主-以横向收缩为主3阶段；（2）土壤蒸发分为稳定、下降和残余阶段，裂隙发育在稳定蒸发阶段；裂隙的不可修复性对后续开裂具有显著影响；（3）微润灌下裂隙面积率和长度密度随深度增加而降低，裂隙纵向发育随水头增加而减弱，施加2.0 g·L-1尿素裂隙最大深度、平均深度减小15.1%和31.5%；（4）裂隙对微润灌湿润体和水分分布有显著影响，其分布不规则程度增加；当裂隙深度为10和15 cm时，分布均匀度降低14.6%~29.3%；（5）裂隙影响湿润锋推进速率，裂隙深度和面积率越大，湿润锋水平运移越慢，竖直方向运移越快。湿润体内距微润管越远，硝态氮含量越高，铵态氮含量越低，受裂隙影响，硝态氮、铵态氮的运移表现出加快、增多的特征；（6）利用PFC2D软件构建了土壤收缩、裂隙水平发育和纵向发育离散元模型；基于土壤收缩特征建立了颗粒半径逐步收缩系数与土壤含水率函数关系，模型有效模拟了土壤收缩和裂隙发育过程；（7）将微润管壁模拟为多孔介质，构建了微润灌水分运移模型，采用实测数据验证了模型有效性；（8）土壤质地黏重则微润灌湿润锋运移越慢，压力水头越高湿润锋运移越快，且管附近饱和度越高；管埋深显著影响湿润体位置，对出流量和湿润锋速率影响较小；（9）提出了微润灌Green-Ampt入渗模型，验证了变工作水头下微润管出流、入渗量和湿润锋推移过程，构建了基于作物腾发的水头调控模式；（10）裂隙深度增加至管埋深时灌水质量降低，裂隙走向和潜在蒸发强度对灌水质量影响较小，管埋深、管间距及压力水头对灌水质量有显著影响；（11）针对大田玉米，基于微润管出水规律，根据作物根系分布特征和耗水特点，提出了大田玉米微润灌溉系统的推荐参数。研究结果为微润灌田间应用、微润管技术参数和管理优化提供了参考。