Study On Yield Gaps And Efficiency Gaps For Rice In Northeast China

Northeast China(NEC)is the main producing area of Japonica Rice in China.The rice planting area and production of NEC accounts for more than 50%of the total area and production of the national Japonica rice.The production of rice in NEC is of great significance for ensuring the national rice grain security.At the same time,NEC is also one of the most significant regions affected by global climate change.At present,the rice actual yield in NEC is far below its potential yield.How to produce more rice by using the limited farmland has become a major problem facing rice production system of NEC.This study divided NEC into four sub-regions:region I Liaoning province,region Ⅱ of Jilin province,regionⅢ of first and second accumulated temperature zones of Heilongjiang province,region Ⅳ of the third and forth accumulated temperature zones of Heilongjiang province according to administrative division and≥10℃ accumulated temperature zone division standard of Heilongjiang province.Based on the meteorological data from 1981 to 2016,statistical data and rice trial data in agrometeorological observation station,ORYZA(v3)rice model,mathematical statistics method and the GIS technology were used together to simulate different levels of rice potential yield and analyse different levels of rice resources efficiency.Besides,the main constraints factors to rice yield gap and resources efficiency gap in NEC,and constraint factor to rice efficiency were revealed and quantified,which will provide a scientific basis for increasing crop production and improving resources efficiency in NEC.The main conclusions are as following:(1)When the varieties and managements were not changed,the maximum,minimum temperature and solar radiation would cause a decrease in rice yield by 228.6 kg·ha-1,143.7 kg·ha-1 and 66.4 kg·ha-1 per decade over the past 36 years,respectively.The changes of scattered radiation percentage had positive impact on rice yield,which improved rice yield by 12%.When the variety renewal was considered,the maximum,minimum temperature and solar radiation would cause a increase in rice yield by 449.2 kg·ha-11,683.1 kg·ha-1 and 677.8 kg·ha-1 per decade over the past 36 years,respectively.The changes of scattered radiation percentage had positive impact on rice yield,which improved rice yield by 11～13%.During 2020 to 2050,rice potential yield showed a decreasing trend of 57 kg·ha-1 per decade.(2)During 1981 to 2016,the mean area-weighted light-temperature potential yield(YP),the yield under high-yield and high-efficiency(YPHH),simulated farmers’ yield(YPSF)and farmers’ actual yield(Ya)were 12978 kg·ha-1,9969 kg·ha-1,7355 kg·ha-1 and 6409 kg·ha-1.The YP decreased from south to north and from west to east.The YP,YPHH,YPSF and Ya have increased by 519 kg·ha-1,237 kg·ha-1,906 kg·ha-1 and 1494 kg·ha-1 per decade during the past 36 years in NEC.(3)During 1981 to 2016,the yield gap between YP and Ya(YGT)of rice decreased from southwest to northeast.The area-weighted rice yield gaps were 6569kg·ha-1averaged over NEC from 1981 to 2016,which accounted for about 51%of the YP of rice.The mean YGT had increased by 210kg·ha-1 per decade in NEC.The yield gap between YPHH and YP(YG1)was 3009 kg·ha-1 averaged over NEC from 1981 to 2016,which accounted for about 23%of YP and increased by 384 kg·ha-1 per decade in NEC.The yield gap between YPHH and Ya(YG2)was 3560 kg·ha-1 averaged over NEC from 1981 to 2016,which accounts for about 28%of YP and increased by 663 kg·ha-1 per decade in NEC.(4)The utilization efficiency of light energy(RUE)and utilization efficiency of heat resources(HUE)under the conditions of light temperature potential,high yield and high efficiency and simulated farmers’management showed a decreasing trend from north to south.During the past 36 years,the overall RUE and HUE showed an increasing trend and the RUE and HUE under the potential conditions were more than which under high yield and high efficiency conditions.The RUE and HUE of simulated farmers’yield were lowest.The utilization rate of light energy showed from high to low,region Ⅰ>region Ⅲ>region Ⅱ>region Ⅳ.The utilization rate of heat resources showed from high to low,region Ⅳ>regionⅡ>region Ⅰ>region Ⅲ.(5)During the past 36 years,the water use efficiency(WUE)under high yield and high efficiency conditions and simulated farmers’ conditions showed an increasing trend.The constraints of farmers,management to WUE were from high to low in the four regions follows,region Ⅰ>region Ⅳ>regionⅡ>regionⅢ.During the past 36 years,the nitrogen fertilizer partial productivity(PFP)under high yield and high efficiency conditions and simulated farmers’ conditions showed an increasing trend.The constraints of farmers’ management to PFP were from high to low in the four regions follows,region Ⅰ>region Ⅳ>region Ⅱ>regionⅢ.