Intelligent irrigation strategy based on regulated deficit theory and fuzzy control for rice in cold region

Heilongjiang Province is the largest rice production base in China, but traditional irrigation method causes severe water waste and nutrient loss. Intelligent irrigation strategy based on regulated deficit irrigation and fuzzy control is a water-saving and energy-efficient method to increase rice yield and quality. Regulated deficit irrigation is a technology that based on the water requirement of rice during different growth stage rather than farmers’ experience, which can effectively improve the utilization of water resources. Automatic irrigation system is a time delay and nonlinear process, which is influenced by many factors(temperature, soil moisture, etc.) and is difficult to establish accurate mathematical models, while fuzzy control is an artificial intelligence method that based on the people’s experience and imitating people’s way of thinking to control complex system with multiple parameters. In this study, the irrigation strategy was composed by fuzzy control module and forecasting irrigation module. Fuzzy irrigation module is a two stage fuzzy control. The first stage fuzzy control determined the optimal current soil moisture. The difference between current soil moisture and optimal current soil moisture, and temperature were taken as input variables for the second stage fuzzy control, to establish the multiple-factor controlled regular database and to realize a fuzzy control of the irrigation time. Soil water loss is mainly caused by evaporation-transpiration and soil water infiltration, which could be estimated by linear regression analysis of environmental parameters. Double loop method was used to measure soil permeability coefficient. The forecasting irrigation module established the soil moisture changing function to forecast when to irrigate by fusing evaporation-transpiration, soil permeability coefficient and meteorological factors. A field research was carried out in Fangzheng County, Heilongjiang Province, and the result showed the water saving rate of regulated deficit irrigation was 20.5%, and the seed setting rate and yield was improved by 4% and 8%, respectively, compared to manual irrigation, which indicated the irrigation strategy used in this study could decrease water waste efficiently and also play critical roles in reducing agriculture production cost, increasing rice yield and improving rice quality.