Rice growth simulation under film mulching in dryland through improving CERES-Rice model

Abstract: The ground cover rice production system (GCRPS) is a potential alternative to the traditional paddy rice production system (TPRPS) by irrigating soil beds mulched with film and maintaining soils under predominately unsaturated condition, and it has become one of the most promising water-saving technologies for rice. The increase of soil temperature effected by film mulching 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. In this study, the sub-modules of soil temperature and soil water in original CERES-Rice model were improved (through changing soil temperature and water conditions based on the relevant research results of the dryland crops) to evaluate the simulation on rice growth in the GCRPS. A 2-year field experiment (2013 and 2014) with 2 treatments. The treatment W1 referred to the traditional treatment with a 2-5 cm water layer on the soil beds but without plastic film mulching, W2 was the film mulching treatment keeping soil moisture in root zone near the saturated content by filling the furrows with water completely but without water layer on the soil beds, and W3 was also the film mulching treatment that was managed as the same way as the W2 before mid-tillering stage and then kept the soil moisture in root zone at 80%-100% of field water capacity). The experiment was conducted in Fang county of Hubei province, located at 32?7?N and 110?42?E to test the feasibility and rationality of the model improvement. Each treatment was replicated 3 times. A total of 9 plots were arranged and each plot was 9 m in wide and 10 cm in length. A seepage-proof material was laid around each plot under the depth of 80 cm to avoid lateral percolation from the neighbor plots. Five soil beds (156 cm wide) in each plot were built for planting rice, 6 lines of rice were planted for each soil bed with the fixed spacing (26 cm between lines and 18 cm between plants). The small furrows (15 cm in width and depth, respectively) were dug around each soil bed. Among the 2 growth seasons, the experimental data (obtained in 2013 and 2014) were used to rectify the simulation models and verify the rectified models, respectively. Based on the measured meteorological data (air temperatures/solar radiation/precipitation etc.), soil data (soil water contents/soil physical parameters/soil organic matter contents etc.) and field management data (irrigation amount/displacement/fertilizing amount by field), the changing processes of rice growth in the W2 and W3 treatments were simulated using the rectified models. The original and improved CERES-Rice models were also used to simulate the change of leaf area index, the aboveground dry weight, and the rice yield during the 2 growth seasons. The results of the comparison showed that the improved CERES-Rice model had remarkable superiority in delineating the effects of changing environments (e.g. soil temperature and soil water) on rice growth and production in the GCRPS. Both of the estimation of the phenological phases and yields were in good agreement with the measured values, and the relative error was not more than 15%. The root mean squared errors (RMSE) between the simulated and measured leaf area index was not higher than 1.54 m2/m2, the correspondingly normalized root mean squared errors (NRMSE) was not higher than 26.59% and the values of modeling efficiency (EF) were not less than 85%. Moreover, the simulated dynamics of aboveground dry weight were compared well with the measured values (RMSE was smaller than 1 490 kg/hm2, NRMSE was smaller than 16%, but EF was not less than 0.95). Therefore, the improved CERES-Rice model is rational and reliable to simulate rice growth and production in GCRPS.