Simulating Crop Growth In A Ground Cover Rice Production System Through By The CERES-Rice Model

The traditional paddy rice production system (TPRPS) characterized by large water consumption is facing unprecedented challenges. It was urgency to develop the water saving rice production system. The ground cover rice production system (GCRPS), a potential alternative to the traditional paddy rice production system (TPRPS) by furrow irrigating film mulched soil beds and maintaining soils under predominately unsaturated condition, has become one of the most promising water-saving rice production technologies and has been found to save water application, increase soil temperature, and reduce nitrogen pollution and methane emission. The effects of soil temperature enhancement by film mulch and the unsaturated root-zone condition should be taken into consideration, when CERES-Rice, a software package widely and successfully applied in TPRPS, is used to simulate rice growth in the GCRPS.In this study, the sub-modules of soil temperature and soil water in original CERES-Rice model were improved to evaluate the effects on rice growth in the GCRPS through referring to some research results from dry land crops. A two-year field experiment (between 2013 and 2014) with three treatments, named as W1 (TPRPS), W2 (i.e. GCRPSsat:keeping root zone average soil water content near saturated), and W3 (i.e. GCRPS80%:keeping root zone average soil water content as 80-100% of field water capacity), respectively, was conducted in Fang county, Hubei province (32°7’N,110°42’E) to test the feasibility of the improvement. The phenological phases, changing processes of leaf area index and aboveground dry weight, and yields of rice in two GCRPS treatments during the two growth seasons were simulated using both the original and improved CERES-Rice models. Comparison results showed remarkable superiority of the improvement in delineating the effect of changing environments (e.g. soil temperature and soil water) on rice growth and production in the GCRPS. Based on the local condition of film mulched irrigation schedules in rice, GCRPSsat、GCRPS90%(keeping root zone average soil water content as 90-100%of field water capacity)、GCRPS80% and GCRPSrain(rainfed irrigation system) were set up and the provised CERES-Rice model was used to model rice growth. The main conclusion of this study were as follows:1. Considering the effect of soil temperature enhancement caused by the ground cover material (chosen as the plastic film in this study) is not involved in the CERES-Rice model, the simulation model of surface soil temperature (at the depth of 5 cm) was referred from other study for dry land crops, and the other one was from CERES-Rice for simulating the subsurface temperatures (at 10 and 20 cm, respectively) in the TPRPS. The simulated and measured surface soil temperatures at 5 cm during both growth seasons were in good agreement, with the root mean squared error (RMSE) less than 1.8℃, normalized root mean squared error (NRMSE) less than 10%, and correlation coefficient (r) higher than 0.89 (P<0.01).The simulated subsurface soil temperatures at 10 and 20 cm in 2013 or in 2014 were also within acceptable ranges, with RMSE<3.2℃, NRMSE<15%, and r>0.65 (P<0.01), respectively, between the measured and simulated values.2. The effects of soil temperature enhancement by film mulch and the unsaturated root-zone condition should be taken into consideration, when CERES-Rice, a software package widely and successfully applied in TPRPS, is used to simulate rice growth in a GCRPS. The sub-modules of soil temperature and soil water in original CERES-Rice model were improved to evaluate the effects (of changing soil temperature and water conditions) on rice growth in the GCRPS through referring to some research results from dry land crops. Both the phenological phases (panicle initiation, anthesis, maturity) and yields were simulated in good agreement with the measured values, with a relative error not more than 15%. The root mean squared errors (RMSE) between the simulated and measured changing processes of leaf area index were not more than 1.54 m2 m-2, and correspondingly their normalized root mean squared errors (NRMSE) were not more than 27%, however, the values of modeling efficiency (EF) were not less than 85%. All of them were within acceptable ranges. Moreover, the simulated dynamics of aboveground dry weight were compared well with the measured values, with RMSE<1490 kg ha-1, NRMSE<16%, but EF>0.95.3. Based on the local condition of film mulched irrigation schedules in rice, GCRPSsat、GCRPS90%、 GCRPS80% and GCRPSrain(rainfed irrigation system) were set up. The improved CERES-Rice simulated rice growth in GCRPS under different irrigation schedule, the result is as follows:for achieving high yield under water sufficient conditions, GCRPSsatand GCRPS90% irrigation system is better. The yield in GCRPSsat and GCRPS90%is 10493 kg ha-1, which increased by 3.1% and 4.8% compared with GCRPS80% and GCRPSrain, respectively; for high efficient water-saving under water insufficient conditions, GCRPSrain irrigation system is ideal. The total water use efficiency (WUET) in GCRPSrain is 1.74 kg m-3, which increased by 45%、30% and 18% compared with GCRPSsat、GCRPS90% and GCRPS80%, respectively.It would be rational and reliable to simulate rice growth and production in GCRPS using the improved CERES-Rice model, which provide a scientific basis for understanding rice crop growth conditions and the environment effect, guiding irrigation, assessing accurately the effect of ecological environment and the sustainable development of local agriculture.