Studies On Characteristics Of Physiology And Biochemistry Of Super Hybrid Rice Nitrogen-saving And High-efficiency Cultivation And Its Key Technique

The Chinese Ministry of Agriculture has established 12 years ago a national collaborative research programme on breeding of super high-yielding rice(super rice).But while China has been successful in breeding super hybrid rice(SHR) strains,it now faces two challenges in developing the super rice:1) because of its higher biomass,SHR.consumes more fertilizers leading to the rapid increase in N fertilizer use,and subsequently causing a series of social and environmental problems;2) the yield potential of super-high-yield varieties could not be attained due to lack of proper cultivation techniques.For these reasons,field experiments were conducted in Changsha,Hunan province in 2006 and 2007 to study N-saving and high-efficiency cultivation of the super hybrid single rice(SHSR).The main results were as follows:1.Yield of SHSR and status of N application in HunanIn Hunan,yields of SHSR ranged from 7.50～9.75 t hm-² Actual yields of 8.25～9.00t/hm² were obtained relative to the variety yield potential of 12.0t/hm².Despite the relatively high level of N application ranging from 225.0kg/hm²ï½ž270kg/hm²,a yield gap of 2.25～4.50t/hm² existed. Thus,Hunan has still a long way to go to improve yield and N-use efficiency of SHSR The basic level of application for N-saving and high-efficiency cultivation of SHSR should be set as 225.0 kg N/hm².2.Genotypic differences in N-use and uptake among super hybrid and middle-season indica rice varietiesResults of this study showed that the order of N harvest index(NHI),N transformation index(NTE),N in grain production efficiency(NGPE) and the N amount needed by 100 kg grain of different genotypes was:NHI＞NTE＞NGPE＞the N amount needed in 100 kg grain.The range of response to N was-2.86～31.06 kg/kg.SHSR.combinations can be divided into 3 types:1) the high N use-efficiency type which can be further subdivided into 2 namely,the high- absorption and use efficiency and low N-tolerance types;2) high yield type with suitable N; 3) high yield type with high N.The low N treatment significantly caused low yield to a greater extent.3.Efficiency of N application using different fertilizers.The grain yield and N uptake and use-efficiency of Sulphur-Coated-Urea(SCU), Coated-Compound-Fertilizer(CCF),LPK/MF and LNPK under two N levels(N-saving and N-equivalent) were much higher compared with the ordinary urea..SCU increased yields by 14.7%～23.9%at 135 kg/hm² and 10.3%～11.9%at 187.5 kg/hm² and had high- N use efficiency.The Physiological efficiency(PE) was over 40 kg/kg and Agronomical efficiency(AE) over 23 kg/kg outweighing ordinary urea by more than 7%and 8%,respectively. Tillering rate,tiller number,effective panicle,photosynthetic leaf area,and dry matter accumulation of super hybrid rice under N-saving condition were lower than those of N-equivalent condition.The maximum tillers and stems significantly decreased,however,the percentage of effective panicle significantly increased.Moreover,the super hybrid ricer had much higher root activity in the middle and late growth stage,higher photosynthetic efficiency, good grain filling and increased number of filled grains.Nitrogen-saving treatments greatly improved N uptake and use-efficiencies,and increased Partial factor productivity(PFP) by 20%, PE by 3.4 to7.2%.AE by 6 to 9.6%,NGPE by 5 to 8.5%,and NIH by 10%.4.Crop growth and development,dry matter production,yield,nutrient uptake,N use efficiencies and soil N accumulation of SHSR under different N-saving treatments.At the range of N applied rate in this study with N level decreasing,tillering rate decreased and the maximum rate and the saturation date of tillering(the tillering rate was 0) and tiller production shortened,the total number of tillers and effective panicles decreased but not significantly.At 135 kg N/hm²(≤40%N-saving),the maximum tillers and stems decreased significantly but the percentage of effective panicles substantially increased.Crop growth rate(CGR) increased with increasing N level.The maximum rates of CGR ranged from 17.5 to 35.9 kg hm^-2d^-1.The correlation coefficients between CGR and grain yield at different stages were as follows:tillering stage(TS) to panicle initiation stage(PI) r= 0.6324 (P＞0.05),PI to booting stage(BT) r= 0.7894(P＞0.05),BT to full heading stage(FH) r=0.9722(P＜0.01),and FH to maturity(MA) r=0.9359(P＜0.01).The dry matter accumulation decreased with N level decreasing.No significant differences in biomass among treatments at the early growth stage,but differences at the middle growth stage were observed except at 135 kg N/hm²(≤40%N-saving).Biomass of N-saving treatments decreased significantly after heading,but with significantly higher amounts and rate of transformation of stem material,sheath material.Grain yield linearly increased with the increasing N application.Maximum yield of 12.0 t/hm² was obtained from the 20%N-saving treatment(180 kg N/hm²) Yield differences between the no N and with N treatments were significant.The yield of N3 treatment was significantly higher than those of the other treatments,except for N4 and N5.Yield differences among N4,N5, N2 were not significant,but their yields were significantly higher than that of N1.Uptake of NPK for SHSR had two peaks.The total N uptake increased gradually with increasing N rate.After heading,the total N uptake of SHSR was about 30%.The rate of N increase in straw was higher than that in grain.The maximum phosphorous uptake was at the middle tillering and potassium just after full heading stages.The percentage K uptake at the later growth stage increased under N-saving cultivation.Nitrogen-saving substantially increased N use efficiency.At 20%to 60%N-saving, Recovery efficiency(RE) increased by more than 42%,AE＞20 kg/kg,PE＞38 kg/kg N,and NHI＞67%.The amount of N required in producing 100 kg grain ranged from 1.53 to 2.19 kg.Effect on soil N accumulation:the total and available N in soil increased with increasing N application.Total and available N in soil of low N treatments significantly decreased,those of the middle N treatments were similar;and those of high N treatments increased significantly. 5.Physiology,biochemistry and photosynthetic traits of super hybrid rice under N-saving cultivationSignificant positive correlation between the chlorophyll content in leaf-area and the amounts of N applied was observed The efficiencies of the chlorophyll content per unit in leaf-area changed from high to low with the increase of N application rate.N-saving treatment could increase efficiencies of the chlorophyll content per unit in leaf-area.Root activities,the activities of NR,GS,and CAT in SHSR.leaves decreased with increasing amount of N applied.The content of MDA in leaves initially decreased and then gradually increased with N application.Root and CAT activities decreased but MDA content increased with growth stage.On the contrary,the activities of GS and NR decreased and reached the maximum at full heading stage.The Pn,Tr,Gs in rice flag leaf increased with increasing rate of N fertilizer.The Ci initially increased and then declined N increased.Optimal range of N-saving improved the maximum photosynthetic rate,reduced the coefficient of light inhibition,and increased light saturation point,but had little or no significant effects on the light absorbing abilities of the rice leaf.Photosynthetic electron transport(ETR),the effective quantum yields(EQY),photochemical quenching coefficient(qP),and non-photochemical quenching coefficient(NPQ) in rice leaf were affected by the amount of N and light intensity.Nitrogen-saving increased but too low or too high N fertilizer decreased ETR,EQY.and qR Non-photochemical quenching coefficient was a positively correlated to the amount of N applied at 10d after full heading(0.9231,P＜0.05).Except for the NPQ,ETR,EQY,qP increased with growth stage.6.The key techniques for super hybrid rice N-saving cultivationThe strategy for N-saving cultivation of SHSR in plain area:the key point was to have effective panicles and balanced grain number and weight.The optimum range of N application rate should be 135～180 kg/hm²,the ratio of N-P-K at 1:0.4 to 0.7:0.9 to 1.2,and the optimum transplanting density should be180,000 hills/hm².The key technique to achieve high yield of super hybrid rice under N-saving cultivation: high N-use efficient varieties,slow/controlled release N fertilizer,early transplanting for stronger seedlings,optimal planting densities,good water and fertilizer-management coupled with integrated pest control and anti-lodging techniques.