Evaluation On Rice Grain Yield And Quality Affected By Altitude,Water And Nitrogen In A Water-saving Ground Cover Rice Production System

China,one of the world’s largest rice producers,is facing serious challenge because of large amount of population and severe water shortage.Especially in high altitude mountainous area,traditional paddy rice production is mostly limited by low temperature in early spring,seasonal water scarcity and insufficient irrigation system.The so-called ground cover rice production system(GCRPS)has been introduced to significantly improve rice grain yield,save irrigation water and reduce greenhouse gas emissions since its application in large scales.However,it remains unknown whether(1)the yield increase rate of GCRPS is larger in high altitude area than low altitude;(2)rice commercial and nutritional quality will change in GCRPS;(3)rice yield in GCRPS will respond to nitrogen application rate,and can hyperspectral calculation equations be established for yield parametres and nitrogen diagnosis in GCRPS?Accordingly,this study will answer the three scientific questions through field experiments,which can provide theoretical foundations for the promotion of GCRPS in larger scales.The study includes three parts:(1)14 pairs of adjacent GCRPS and Paddy fields at altitudes of 900 m and 23 pairs at 500 m altitude were sampled with 3 replicates in Hubei Province,central China.We hypothesised that yield advantage of GCRPS over traditional Paddy might become larger at higher altitudes.Rice yield and yield parametres were determined,the mechanism of yield increase were discussed.(2)A three-year field experiment in Hubei Province was conducted comparing three production systems:traditional paddy,GCRPS water saturated and GCRPS 80%of soil water holding capacity.Production systems were combined with three nitrogen fertilizer regimes:nitrogen absence,urea as basal fertilizer,urea split application/urea plus chicken manure.Rice yield,especially grain milling,appearance,eating and nutritional quality was analysed.(3)Nitrogen application rate experiment was conducted comparing five nitrogen levels,yield,yield parametres and 6 types of canopy hyperspectral indices were determined.Our results showed that:(1)Rice grain and straw yield were 40%and 35%greater in GCRPS compared to Paddy at 900 m,while the difference was only 10%and 15%at 500 m.Compared to Paddy,increase in productive tiller numbers,spikelets per square metre and percentage of filled grains were significantly larger in GCRPS at high than at low altitude.No significant differences were observed between production systems and between altitudes with respect to soil properties.Soil temperature differences between GCRPS and Paddy were significantly higher at 900 m than at 500 m during the first month after transplanting.Our findings demonstrate that GCRPS has a good potential to increase rice yield in mountain regions with high altitudes where rice production is limited by low temperature and seasonal water shortage(Third Chapter).(2)In GCRPS,grain milling quality was significantly improved by the increase milled rice rate.Amylose concentration and chalky rice rate were significantly higher,while protein and amino-acid concentration was significantly lower in GCRPS than in Paddy.However,yield of protein and total amino acid were significantly higher in GCRPS than in Paddy.There is no difference between concentration of six essential amino-acids,while non-EAAs were higher in GCRPS than Paddy in nitrogen split application.Our results show that suitable N management practices still should be improved for GCRPS in order to further enhance the protein and amino acid concentrations(Fourth Chapter).(3)Rice grain and straw yield were significantly increased with higher nitrogen application in GCRPS.Productive tillers and spikelets per panicle are increased with higher nitrogen application.There is a significantly positive correlation between the ratio vegetation index in green band RVI-2 and yield,yield parameters,nitrogen use efficiency.Equations are established to calculate rice yield parametres with hyperspectral data.Our results provide an efficient way for rice nitrogen diagnosis and optimization in ground cover rice production system(Fifth Chapter).