Water Consumption And Water-saving Characteristics Of A Ground Cover Rice Production System

The traditional paddy rice production system (TPRPS) characterized by large water consumption and low water use efficiency is facing unprecedented challenges. It was urgency to develop the water saving rice production system. Among many water saving rice production system, the Ground Cover Rice Production System (GCRPS) recognized as new water saving rice cultivation technique has been attracted widely attention among researchers. At present, most of the researches regarded to the GCRPS have been focused on the comparing yield effects of GCRPS, while the regularity of water consumption, the water component and water-saving characteristic under GCRPS have been rarely reported.In this research, the field experiment in Fangxian County, Hubei Province and soil column experiment in greenhouse were conducted to study the mechanism of water saving and increasing production (GCRPSsat and GCRPSgo%) under GCRPS. The regularity of water consumption and water-saving characteristic under GCRPS were illustrated in this research; the rice growth, physiological characteristic and rice yield under GCRPS were investigated; the water use efficiency was evalueated; the root water uptake model based on the root length density was established, and then the root water uptake model was combined with the stomatal conductance model involving root-sourced ABA signals, simulating the daily variation of stomatal conductance. Through the present studies, the main results were obtained as follows:(1) The total water consumption (irrigation and rainfall) decreased 34.6% under GCRPSsat and 47.4% under GCRPS80% respectively comparing with the TPRPS. The irrigation of GCRPSsa, and GCRPS8o% reduced 61.3% and 83.8% respectively. The reduction of irrigation water under GCRPS was attributed to the decrease of the non-physiological and physiological water consuming. Comparing to TPRPS, the deep percolation and water evaporation of GCRPS decreased 71.5-88.2% and 82.8-89.1% respectively; rice transpiration decreased by 6.1-9.7%. The transpiration varied among treatments in different growth stage of rice due to different effects of the LAI and stomatal conductance.(2) In filed experiment, the results indicated that the leaf area and aboveground biomass of GCRPS was significant increased compared to TPRPS; the root biomass, root length density and root diameter were all increased significantly under GCRPS treatments in max-tillering stage, while that were decreased (especially the root diameter) in anthesis stage with no significant difference between treatments. GCRPS decreased root:shoot ratio compareing to TPRPS. The similar biomass and yield of were observed under GCRPSsat and GCRPS80%, which increased by 15.7% and 11.0% compared with TPRPS. In greenhouse experiment, the results indicated that the leaf area, aboveground biomass, root biomass, root length density and yield in GCRPSsa, had no significant difference with TPRPS, while that were significantly decrease in GCRPS80% and GCRPSfwc,c due to water stress for long time.(3) Water use efficiency (WUE) was defined at different scales for different water related parameters. In this study, refered WUE inculded toal water use efficiency(WUE1-P), irrigation water use efficiency(WUE1), transpiration water use efficiency (WUEr) and photosynthetic water use efficiency(WUEphow).Comparing with TPRPS, the water use efficiency of total water input and irrigation for GCRPSsat were increased by 70.7% and 194.2%, and which increased by 110.3% and 608.7% for GCRPS80% treatment. The transpiration water use efficiency and photosynthetic water use efficiency were also increased significantly under GCRPS. The leaf δ13C for GCRPS treatment was significantly increased and significantly correlated to the transpiration water use efficieny.(4) According to transpiration water consumption of rice, the root uptake model based on the distribution of root length density was established in this research, and well described the variation of root water uptake in different soil layers. The root water uptake model was substituted for Penman-Monteith equation in the stomatal conductance model involving root-sourced ABA signals. The simulation results showed that the coupled model more accurately depicted the ABA production processed in root system, root ABA concentration in different soil layers and the contribution to ABA concentration in xylem, and finally adjusting stomatal conductance behaviors, and improved the simulation precision of the original model.