| Agricultural production system is a complex dynamic system, which is influenced by climate, soil, cultivars and management practices. So there is a great challenge for agricultural workers to comprehensively consider the effects of multi-factors interaction on crop production, because of the spatial and temporal variability of natural environment. However, crop growth simulation models could quantitatively describe and dynamically simulate the crop growth development and yield formation. It is an efficient means to assess the impact of environment and human activity on crop productivity, especially in regional area.Therefore, in this study we combined an analysis of climate and observed rice growth data with rice growth modeling (RiceGrow) to analyze the climate change during the rice growth periods and investigate the impact of changes in climate, rice cultivars and agronomic management on rice productivity in China. In addition, we combined the weather data, soil nutrients data, cultivars and management information in1980s and2000s with rice growth model (APSIM-Oryza) and GIS technology to simulate and quantify the effects of climate change, soil improvement, cultivars update and management practices change on rice productivity.According to the regionalization of rice cropping in China with rice planting area, grain yield per unit, total grain yield, weather station locations and observed rice data locations, seven typical rice planting sites were selected in this study, which cover single and double rice cropping area (single rice cropping area includes Wuchang in Heilongjiang Province, Xinyang in Henan Province, Zhenjiang in Jiangsu province and Hanyuan in Sichuan Province; double rice cropping area includes Nanchang in Jiangxi Province, Hengyang in Hunan Province and Gaoyao in Guangdong Province). In this paper, the trends over time for each climate variable during the rice growth stages and the length of each stage were tested for significance at the5%level using the Student’s t test. The statistical method was used to quantify the contributions of temperature and variety changes to variations in observed growth durations, and the effects of cultivar characteristics and agronomic factors on observed rice yields. The results in this study showed that the changes in climatic variables were not uniform between the single and double rice cropping areas. In the single rice cropping system (Wuchang, Xinyang, Zhenjiang and Hanyuan), the main changes of climate were increased in temperature and decreased in precipitation and sunshine hours. However, the main changes of climate in double rice cropping system (Nanchang, Hengyang and Gaoyao) were increased in temperature and precipitation and decreased in sunshine hours. In addition, the scope of climate change in single rice cropping system is greater than that in double rice cropping area. From1981to2009, the average maximum temperature during the whole growth period was increased by0.039℃per year at Wuchang,0.029℃per year at Xinyang,0.058℃per year at Zhenjiang and0.029℃per year at Hanyuan. The average minimum temperature was increased by0.087℃per year at Wuchang,0.029℃per year at Xinyang,0.068℃per year at Zhenjiang and-0.001℃per year at Hanyuan. The temperature difference was increased by-0.048,-0.005,-0.010and0.039℃per year at Wuchang, Xinyang, Zhenjiang and Hanyuan, respectively. The total sunshine hours during the whole growth period was decreased by-4.80,-8.29,-1.56and-2.37hours per year at Wuchang, Xinyang, Zhenjiang and Hanyuan, respectively, and the total precipitation was declined by-4.89,-1.26,1.00and-0.46mm per year. In double rice cropping system, the average maximum temperature has been increased by0.029,0.045and0.019℃per year at Nanchang, Hengyang and Gaoyao for early rice and0.068,0.029and0.003℃per year for late rice. At Nanchang, Hengyang and Gaoyao the average minimum temperature was increased by0.012,0.039and-0.001℃per year for early rice and0.077,0.039and-0.001℃per year for late rice. The temperature difference was increased by0.013,0.008and0.016℃per year for early rice and-0.003,-0.010and0.016℃per year for late rice at Nanchang, Hengyang and Gaoyao, respectively. During the whole rice growing period, the total precipitation at three double study sites was almost stable. The changes of sunshine hours at Nanchang and Hengyang for both early and late rice did not reach the significant level. However, the sunshine hours changed significantly at Gaoyao for both early and late rice and the scope is-6.86and-6.03hours per year.One typical rice cultivar and traditional management practice in1980s was used in the model at each site for climate change simulation. The results showed that if there were no varieties, soil and management change, the global warming could have shortened the rice growing period and reduced the grain yield in both single and double rice cropping systems during the study period (1981-2009). From1981to2009, the duration of the whole growing period would have been shortened by10.4,12.315.7and8.4days at Wuchang, Xinyang, Zhenjiang and Hanyuan, respectively. At Nanchang, Hengyang and Gaoyao, the duration of the whole growing period would have been shortened by8.4and10.6,8.1and2.8,2.8and1.7days for early and late rice. The simulation results also showed that the changes of climate in the past3decades could have declined the rice yield. The potential and rainfed yields have been decreased by1038and1029kg-ha"1at Wuchang,1827and2024kg·ha-1at Xinyang,945and1012kg·ha-1at Zhenjiang and96and841kg·ha-1at Hanyuan. At Nanchang, Hengyang and Gaoyao, the potential and rainfed yields have been decreased by609and50kg·ha-1,661and284kg·ha-1,476and357kg-ha’1for early and late rice.Further analysis of rice phenological parameters in the model showed that the varietal changes are mainly due to changes in intrinsic earliness (IE)(affecting the stage from sowing to jointing) and basic filling factor (BFF)(affecting the stage from heading to maturity). Compared the observed rice growth period data with the simulated one, we found that the improved cultivars could compensate the negative impact on rice growth period by global warming in single rice cropping area and improved the rice yield. However, the improved cultivars in double rice cropping area could not offset the negative impact on rice growth period caused by global warming, but could improve the yield for both early and late rice.According to the statistical analysis, we found that the improved harvest index and grain numbers per spike contributed significantly to increase rice yield. Further analysis showed that the improvement of harvest index was mainly attributed to the increased grain numbers per spike. From1981to2009, the harvest index increased by0.12,0.09,0.29and-0.03at Wuchang, Xinyang, Zhenjiang and Hanyuan, respectively. At Nanchang, Hengyang and Gaoyao, the harvest index increased by0.12and0.15,0.06and0.06,-0.03and0.23for early and late rice, respectively.The climate and soil data in1980s and2000s in Taihu region were analyzed by GIS technology. During the whole rice growing period, the average maximum, minimum temperature and the temperature difference in2000s in the Taihu Region were higher than that in1980s, while the total precipitation (except for northeast) and sunshine hours were lower than that in1980s. The declining of precipitation from jointing to heding and from heading to maturity was the reason of declining of total precipitation in the whole rice growing period. However, the declining of sunshine hours from jointing to heading was the reason of declining of total sunshine hours in the whole rice growing period. Compared with the soil nutrients data in1980s, the mean contents of soil organic matter, total nitrogen, available phosphorus and potassium in2000s in the Taihu Region increased by15.85%,79.55%,195.72%and10.37%, respectively. The average grain yield in2000s in the Taihu Region was increased by46.3%, which was caused by the interaction of climate, soil nutrients, cultivars and management. The contributions of climate, soil nutrients, cultivars and management on rice productivity were different. Compared with1980s, the yield in2000s decreased by19.5%which was caused by climate change, while the yield was increased by21.7%and34.6%due to cultivars update and management practices change, respectively. Without fertilizer application (assume the fertilizers rate is0in both1980s and2000s), the yield was increased by12.7%due to soil improvement. |
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