轻小型喷灌机组变量运行对肥液输运及沉积的影响机理

The variable rate irrigation is an important part of the high efficiency agriculture. However, the precision control of water and nutrient remains a challenge. Irrigation with low pressure sprinklers is liable to cause nozzle clogging, but the deposition of the clogs usually happens during the process of fertilizer solution transport. Thus, the hydraulic condition and the transport mechanism of the fertilizer solution in the small-scale irrigation system under variable rate operation are investigated by theoretical analysis and experimental methods. Based on the hammer theory, a hydraulic calculation model for the pump-fertilizer applicator-pipeline coupling is proposed concerning the transient characteristics of the hydraulic condition when the fertilizer applicator is started or stopped and when the system is under variable rate operation. A transport model of the fertilizer solution in the pipe with multiple outlets is formed based on the mass transfer theory. And it is applied in the exploration of the impact of fertilizer concentration and hydraulic parameters on the uniformity of fertilizer both within the pipe and on the watered ground. A deposit model of chemical solute is established considering the local equilibrium in the precipitation system of fertilizer in the irrigation water. And the model is then introduced in the analysis of the distribution of chemical deposits in the irrigation system. The performance of the variable rate operation conditions in alleviating the nozzle clogging is explored numerically and experimentally. This research is attempted to reveal the hydraulic balance mechanism in the variable rate operation of the irrigation system and its effect on the transport and deposit of fertilizer solution, which will provide some theoretical and technological basis for the precision control of variable rate irrigation systems and the study on the chemical transport in the soil.

变量灌溉技术是高效农业的重要组成部分。但水分及养分的精确控制一直是研究的难点。低压灌溉易引起喷头堵塞，但堵塞物的沉积与肥液的输运过程通常相伴发生。本项目采用理论分析与试验研究结合的方法，对轻小型喷灌机组不同变量运行模式下的水力状态、肥液输运规律进行研究。以水锤理论为基础，提出考虑施肥泵启闭及变量运行瞬态特性的水泵-施肥泵-灌溉管道水动力耦合计算模型；以传质理论为基础，构建肥液在多口出流管道中的输运模型，研究肥液浓度及水力参数变化对管道中和灌溉地面肥液分布均匀性的影响；提出基于灌溉水中沉淀体系局部平衡的盐类沉积模型，研究灌溉系统盐类沉积分布规律，通过模拟与试验探索不同变量运行模式对灌溉堵塞的改善作用。本项目旨在揭示喷灌机组变量运行水动力平衡机理，及对肥液输运、沉积过程的影响规律，为变量灌溉机组精确控制、盐类迁移过程等方面的研究提供理论和技术基础。

变量灌溉是高效农业的重要组成部分。但水分及养分的精确控制一直是研究难点。变量喷灌系统中不同工况下肥液的输运和沉积是影响水肥分布均匀性的关键因素。因此，本项目针对轻小型喷灌机组不同变量模式下的水力状态、肥液输运规律、水肥分布均匀性进行研究。以入口压力、流量和母液浓度为自变量建立施肥泵质量流量吸肥模型，首次提出水泵-施肥泵-灌溉管道水动力耦合计算模型；通过仿真分析探明不同变量运行工况下系统水力状态切换规律。结果表明，比例式施肥泵活塞的周期运动对水泵状态的变化有一定的缓冲作用，使水力状态切换更加平稳。基于试验的手段，研究了水力因素（喷头工作压力、相邻喷头工作压力差）以及施肥参数（施肥泵进出口压差、施肥浓度）对水肥分布均匀性的影响，并建立了水、肥分布均匀性的多元二次预测模型。结果表明各因素对水肥分布均匀性的影响具有强非线性。与清水灌溉相比，采用比例施肥泵施肥时其活塞周期运动会使喷头远处动能减少，近处水量增加；施肥泵进出口压差增大时，其运动频率增加使得喷洒出的水流近处远处相互补充，肥液分布均匀性有所提高，但也使得施肥量分布均匀性变化更加剧烈。同时研究了管道首末水肥分布差异，以及管道布置方式对水肥输运及分布均匀性的影响。分析表明管道末端施肥量均匀性下降明显。并且，通过研究施肥及冲洗过程中各测点肥液浓度的动态变化规律分析肥液沉积的风险。试验表明，水、肥在输运过程中存在时间与空间上的不同步性，管道末端节点施肥延迟时间与冲洗时间受流量和压力递减的双重影响。并总结得出喷头堵塞改善措施。当施肥泵D8R配置喷头10PY2H时，最佳参数组合为工作压力0.22MPa、进出口压差为0.06MPa、肥液浓度为35g/L。研究成果对变量喷灌施肥系统优化设计、精准施肥、多过程协同调控具有一定的工程和学术价值。本项目研究成果多发表在本领域一流期刊，包含Agricultural Water Management、Biosystems Engineering、农业工程学报等，并出版学术专著1部，授权专利多项。