Agronomic And Physiological Traits For Rice Cultivars Differing In Response To Nitrogen

Rice is one of the most important food crops in China.To reduce the pressure of increasing food demand due to the population increase,China has paid a great attention to increasing grain yield per unit area in rice production.On the other hand,with the increase in rice yield,the application of chemical fertilizer,especially nitrogen(N)fertilizer,has been dramatically increased.Excessive application of N fertilizer has become a serious problem in rice production in this country.Breeding and selecting N-sensitive and high-yielding cultivars[grain yield and N use efficiency(NUE)are higer at a lower N rate]is an important way to increase crop yield and NUE.However,the agronomic and physiological trait for N-sensitive and high-yielding rice cultivars is not clear,and little information is available on the fertilizer and water management technology for rice cultivars differing in response to N.In this study,rice cultivars with different responses to N were used as materials,and the evolutionary characteristics of rice cultivars applied in different decades,agronomic and physiological traits of shoots,morphological and physiological traits of roots and their relationship with grain yield and NUE were investigated.The effect of N management and irrigation regimes on grain yield,NUE and grain quality and its physiological mechanism were studied.The main results are as follows:1.Differences in response to N for rice cultivars applied at different decadesTwelve typical indica rice cultivars and 12 typical japonica rice cultivars applied in the production in Jiangsu Province during the last 70 years were used,three N levels of zero N,medium amount of N and high amount N,were applied.Changes in grain yield(GY)and response to N were studied.The results showed that GY and NUE were progressively increased with the improvement of cultivars at each N level.Cultivars applied in different decades showed a strong genetic difference in the response to N levels.Modern cultivars showed higher GY and NUE than early-bred cultivars at the high N rate,and GY and NUE of early-bred cultivars were decreased at the high N level when compared to those at the medium N level.The higher grain yield and NUE for super rice cultivars were mainly attributed to their greater total spikelet number and more spikelets per panicle.However,a lower filled-grain percentage for super rice limited its yield potential.It would be an important approach to further increase GY and NUE for super rice through increasing filled-grain percentage.2.Agronomic traits for rice cultivars differing in response to NEleven typical japonica cultivars currently used in Jiangsu Province were grown in paddy field with two treatments of ON(zero-N control)and 200N(200 kg N ha-1),and GY,response to N and the main agronomic traits for N-sensitive and high-yielding cultivars were studied.The results showed that,when compared with N-insensitive cultivars(grain yield and NUE are lower at a low N rate),N-sensitive and high-yielding cultivars exhibited higher dry matter accumulation and harvest index,greater total spikelet number and the percentage of productive tillers,larger total leaf area index,effective and highly effective leaf area index,higher grain-leaf ratio(spikelets to leaf area,filled grain to leaf area,and grain yield to leaf area).The correlation analysis showed that there were significant and positive correlations between agronomic traits and GY and NUE.These agronomic traits could be used as indexes for screening N-sensitive and high-yielding rice cultivars.3.Shoot physiological traits for rice cultivars differing in response to N Two N-sensitive and high-yielding cultivars and two N-insensitive cultivars were grown in the field with two N rates,0 N and 200 N kg ha-1,and GY,NUE and shoot physiological traits were investigated.The results showed that,when compared with the N-insensitive cultivars,the N-sensitive and high-yielding cultivars had a higher photosynthetic rate and N accumulation,stronger activity of the enzymes involved in N metabolism,higher photosynthetic NUE,more accumulation of soluble sugars and starch in stems and sheaths at heading time,and more remobilization of nonstructural carbohydrate from stems to grains during grain filling,which were the important physiological traits achieving higher GY and NUE for the N-sensitive and high-yielding cultivars.4.Root morphological and physiological traits for rice cultivars differing in response to NTwo N-sensitive and high-yielding cultivars and two N-insensitive cultivars were grown in the field and four N rates,0,100,200 and 300 N kg ha-1,were applied during the growing season.Root morphological and physiological traits for rice cultivars differing in response to N were investigated.Results showed that N-sensitive and high-yielding cultivars produced higher GY,took up higher amount of N from soil,and exhibited higher NUE than N-insensitive cultivars at lower N rates(0,100 or 200 kg ha-1).GY and NUE were comparable among the four cultivars at the N rate of 300 kg ha-1.When compared with N-insensitive cultivars,N-sensitive and high-yielding cultivars had greater root and shoot biomass,deeper root distribution,longer root length,greater root length density,root oxidation activity,total absorption area and active absorption area at lower N rates,suggesting that N-sensitive and high-yieldingt cultivars can maintain grain yield at lower N rates.The root traits,especially the deeper roots,greater root oxidation activity at lower N rates,could be used as indexes in selection for N-sensitive and high-yielding cultivars.5.Effect of N management on grain yield and NUE for rice cultivars differing in response to NTwo N-sensitive and high-yielding cultivars and two N-insensitive cultivars were grown in the field with four N management treatments including zero-N control(ON),farmers' N practice(FNP),site-specific N management(SSNM)and the management of reduced N rate and more proportion of N applied at late season(RNM).The effect of N management treatments on GY and NUE was studied.The results showed that,when compared with FNP,SSNM and RNM increased GY and NUE for both N-sensitive and high-yielding cultivars and N-insensitive cultivars,with more increases for the former than for the latter.There was no significant difference in grain yield between FNP and RNM.Leaf area index and photosynthetic potential from heading to maturity,and root oxidation activity,leaf photosynthetic rate,remobilization of N and nonstructural carbohydrate from vegetative tissues to grain during grain filling were significantly higher under SSNM or under RNM than under FNP treatments,with more significant for N-sensitive and high-yielding cultivars than for N-insensitive cultivars.6.Effect of N management on grain quality for rice cultivars differing in response to NTwo N-sensitive and high-yielding cultivars and two N-insensitive cultivars were grown in the field with four N management treatments including zero-N control(ON),farmers' N practice(FNP),site-specific N management(SSNM)and the management of reduced N rate and more proportion of N applied at late season(RNM),and the effect of N management on rice quality was observed.Compared with FNP,SSNM and RNM significantly increased head rice percentage,gel consistency,hot viscosity,breakdown value,and the contents of albumin and glutenin,and reduced chalkiness,amylose content,and gelatinization temperature.The results indicate that SSNM and RNM could improve rice quality for both N-sensitive and high-yielding cultivars and N-insensitive cultivars.Compared with N-insensitive cultivars,N-sensitive and high-yieldingt cultivars showed better milling quality,cooking and eating quality and starch viscosity property,higher content of albumin and glutenin,lower amylose content,and more sensitive to N managemt.7.Effect of irrigation regimes on grain yield,NUE and grain quality for rice cultivars differing in response to NTwo rice cultivars,a N-sensitive and high-yielding cultivar Huaidao 5 and a N-insensitive cultivar Yangjing 4038,were used and two irrigation regimes,alternate wetting and dryng(AWD)and convential irrigation(CI),were conducted during the growing season.The effect of AWD on grain yield,water use efficiency(WUE),NUE and rice quality were studied.The results showed that AWD significantly increased grain yield,WUE and NUE compared with CI.When compared with CI,AWD significantly reduced irrigation water,increased fillerd-grain percentage,grain weight,internal NUE,N harvest index,partial factor productivity,protein content in grain,gel consistency,peak viscosity,hot viscosity and breakdown value.N-sensitive and high-yielding cultivars were more sensitive to irrigation regimes compared with N-insensitive cultivars.