Hydrodynamic Modeling And Application Based On SPAC System

Intelligent irrigation is the key to save agricultural water use, and the core of intelligent irrigation is to develop models for water dynamics in the Soil-Plant-Atmosphere Continuum(SPAC) for irrigation decision-making. The research in soil water dynamics is helpful to understand soil water movement, and thus to apply water-saving irrigation in agriculture for an increase in water use efficiency and saving the costs. The systematic study into water dynamics in the SPAC system was carried out based on the integration of the knowledge from the aspects including the basic theory and principles of the SPAC dynamic system, numerical simulation and model validation.First, numerical simulations of irrigated amount, infiltration rate, runoff and soil wetting depth for three typical soils(sandy loam, loam, clay loam) were performed using the HYDRUS-1D model, for the purposes of determining the maximum irrigation rate and the changes in soil water content in the profile immediately after irrigation and 24 h after irrigation. Results show that soil water content in the profile in the sandy loam soil varied relatively rapidly. Infiltration rate and soil wetting depth were greater than those in other two soils. Due to the poor infiltration capacity, the changes in soil water content in the profile were slower in both loam and clay loam soils. The irrigation rate in the sandy loam soil could set to be 5cm/h, while the corresponding values were about 1.0cm/h and 0.l3cm/h for loam and clay loam soils, respectively. Also, it is essential to take into consideration of the changes in the wetting depth caused by re-distribution of soil water content.Second, by introducing the dual crop coefficient approach to estimate soil evaporation and crop transpiration recommended by the FAO, a module for calculating daily evapotranspiration was devised based on weather information and crop development stages. A new model for water dynamics in the SPAC system was developed, and the validation was carried out against data from two Dutch experiments on wheat. Results show that the simulated soil water content values in the profile gathered from time intervals were in good agreement with measurements. The simulated soil evaporation and crop transpiration were reliable. Both soil evaporation and crop transpiration were affected by rainfall, and soil water content was clearly influenced by root water uptake. This indicates that the proposed model was reasonable, and this could be used for water management in crop production.Finally, an overview of hardware and software in the intelligent irrigation system was described, and the strategies for intelligent irrigation were devised for two different circumstances. For the simulated soils in this study, simplified relationships between the soil wetting depth and irrigated amount were established. The principles for automated irrigation were determined and the applications of such principles to crops were carried out. When the soil hydraulic properties were unknown, an approach of using transfer functions and fuzzy mathematics was proposed for water-saving irrigation.