| Rice is one of the most important stable food in China,and its annual production is critical to the country's food security and social stability.The sustainability of future selfsufficiency depend largely on the capacity of rice exploitable production.To assess this capacity,we evaluated current farm yields,potential yields and yield gaps to estimate rice production potential in China and the existing space for production improvement by commonly used international yield gap assessment system.Furthermore,since many researches showed that rice yield was stagnated in the Middle and Lower Reaches of Yangtze River Valley(MLYRV),which is the most important rice production region in China,our study tried to explore ways in both genotype and management practices to increase rice production and ensure food security in this region.Therefore,we carried out simulations and experiments as follows:(1)Calibration and validation of the model ORYZA v3 by representative varieties from different rice growing regions for the simulation of potential yield;(2)Estimation of China rice potential yields and yield gaps,and we also separated cropping systems into single-and double-rice systems for the systematical and comprehensive yield comparisons;(3)Simulating the potential yield of Indica-Japonica rice cultivar in the MLYRV to further explore ways to increase the potential yield in the MLYRV;(4)Experiment of five cultivars and three sowing dates were set under irrigation conditions to acquire different combinations of T&R.Various morphological,yield-and quality-related traits were investigated to identify the optimal T&R for both yield and quality in this region.The main results were as follows:1.After calibration,the model of ORYZA v3 can simulate potential yield well in the major rice growing regions in China.During the calibration process,yield,aboveground biomass and growth period were respectively 0.94 t/ha,1.05 t/ha and 4 d in terms of RMSE,were respectively 9%,5% and 5% in terms of RMSEn,and were 0.83,0.87 and 0.97 in terms of R2 value.Besides,the RMSE and RMSEn value is small and the R2 value is close to 1 during the validation process.These results well proved that the model can simulate high-yield rice growth process and dry matter allocation properly,and thereby can simulate yield properly.2.After the upscaling of yields,the national average potential yield and current farm yield were 9.76 t/ha and 6.78 t/ha,respectively,with a yield gap of 2.98 t/ha.The national yield gap was 31% of potential yield.For different cropping systems,our results showed that the average yield of single-rice system was 28% of the yield potential and was 34% of the yield potential in double-rice system.In terms of yield per hectare,double-rice system had great potential for further increase.In terms of exploitable production(80% of potential production),although single-rice system and double-rice system had similar potential for total production improvement(7-8%),the production contributed by double-rice system to total production was greater than that by single-rice system before current yield reaching 80% of yield potential.Furthermore,in the major rice growing regions,the potential yields and current farm yields were the largest in the MLYRV,and the yield gaps were smallest.In the case of major rice growing provinces,Hunan,Heilongjiang and Jiangxi had the largest current rice production and exploitable production.3.By estimating different scenarios in the future(2030),we explored the relations between rice self-sufficiency ability and closing yield gaps in China.The typical scenarios and results were as follows:(1)If the current yield gap was closed to 26% of the potential yield,rice production would be self-sufficient by 2030;(2)If the yield gap was closed to 20% of the potential yield,the total production would be 19 Mt more than the estimated demand,which equaled to the total production of 8% of paddy fields;(3)If farm yield and cultivated land remains current level,11 Mt rice would be needed in 2030 to meet China rice self-sufficiency,equivalent to 18% of the production of current global rice trade,which might have an effect on international rice market;(4)If farm yield remains at the same level and the cultivated land is reduced by 10%,it would require an extra of 32 Mt to meet self-sufficiency,equivalent to about 50% of the current global rice trade,which would have a huge impact on the international rice market.4.The potential yield of Indica-Japonica rice cultivar Yongyou 12 was 13.90 t/ha,and the yield gap was 6.15 t/ha in single-rice system in the MLYRV.Therefore,the current farm yield was 55% of the potential yield,and there still has 45% of yield gap to close.If Indica-Japonica hybrid rice cultivar was used in single cropping system in the MLYRV,the potential yield of single-rice system in China can be increased by about 20%,and even other regions maintaining current rice production,rice production in China would not only meet people's rice demands,but also have an extra of 6 Mt by the year 2030.5.According to the temperature variation in different sowing date treatments in five cultivars,temperature characteristics in MLYRV were classified into three major combinations,namely,HL,MM and LH.The average daily temperature in LH combination was lower(at least 2oC)in vegetative stage than in grain filling stage.MM combination had similar average daily temperature(around 26oC)in both vegetative and grain filling stage.Opposite to LH,the average daily temperature in HL combination was higher(at least 2oC)in vegetative stage than in grain filling stage.Most of the cultivars had the highest yield and quality with the highest T&R use efficiency in HL combination compared to the other two combinations.By analyzing three combinations,it can be concluded that when the average radiation was above16 MJ m-2 d-1 in vegetative stage,and temperature was in the range of 26-28 oC and 22-27 oC in vegetative and grain filling stage,respectively,the relative yield was higher than 1,which was benefit to high yield.Besides,through linear analysis,yield,quality and resource utilization efficiency were the highest when the vegetative and grain filling temperature were respectively 28 °C and 22 °C. |
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