Effects Of Cultiation Pattern On Rice Yield And Nitrogen Use Efficiency And Its Physiological Mechanism

Excessive application of nitrogen(N)fertilizer and low N use efficiency(NUE)are serious problems in rice production in China,which could not only cause waste of resources and decrease economic benefits,but also result in environmental pollution.It should have great significance to realize the green and high yield of rice,increase the efficiency and protect environment through exploring cultivation methods of synergistic increases in rice grain yield and NUE and elucidating their physiological mechanism.Using two super rice varieties,an indica/japonica hybrid Yongyou 2640 and a japonica inbred Wuyunjing 24,this study designed nine cultivation patterns including no N application(ON),local farmer's practice(LFP,control),reduction of N(RN),increase in plant density and decrease in N rate(IDRN),precise irrigation(PI),application of cake fertilizer(ACF),deep plowing(DP),application of silicon zinc fertilizer(ASZF),and application of earthworm manure(AEM).Effects of cultivation patterns on the growth and development of rice,canopy photosynthetic and physiological indexes,root physiological characteristics,grain yield and its components were investigated.Such a study is expected to exploit cultivation ways to achieve high NUE and understand the physiological mechanism in super rice.The main results are as follows:1.Grain yield and population growth and development characteristicsThe grain yield of Yongyou 2640 under IDRN,PI,ACF,DP,ASZF and AEM was 11.58 t hm-2,12.27 t hm-2,12.91 t hm-2,13.20 t hm-2,.13.77 t hm-2 and 11.63 t hm-2,respectively,and increased by 7.42%,13.82%,19.76%,22.45%,27.74%and 7.88%,respectively,compared with that under the LFP(control).The grain yield of Wuyunjing 24 under IDRN,PI,ACF,DP,ASZF and AEM was 9.53 t hm-2,10.54 t hm-2,10.91 t hm-2,11.0 t hm-2,11.81 t hm-2 and 9.59 t hm-2,respectively,and increased by 3.59%,14.57%,18.59%,20.00%,28.37%and 4.24%,respectively,compared with that under the control.Compared with the control,IDRN,PI,ACF,DP,ASZF and AEM significantly increased the percentage of the productive tillers by 1.83%-10.34%,non structural carbohydrate(NSC)remobilization from stems to grains by 10.63%-71.20%,dry matter by 5.19%-24.99%,leaf area index(LAI)by 5.35%-22.18%,the efficient LAI by 3.60%-9.31%,the high efficient LAI by 2.87%-8.99%after heading,for Yongyou 2640.These cultivation patterns also significantly increased photosynthetic rate of canopy and the grain-leaf ratio.For Wuyunjing 24,IDRN,PI,ACF,DP,ASZF and AEM significantly increased the percentage of the productive tillers by 2.08%-7.71%,NSC remobilization by 19.76%-70.36%,dry matter weight by 2.81%-26.54%after heading,LAI by 7.19%-28.44%,efficient LAI by 3.52%-6.58%,high efficient LAI by 3.79%-9.25%after heading,and significantly increased photosynthetic rate of canopy and the grain-leaf ratio.The results indicate that population quality can be improved,source-sink relationship be optimized,and consequently,grain yield be increased through the improvement in cultivation practices.2.Nitrogen use efficiencyImprovement in cultivation practices increased each NUE index.For example,agronomic use efficiency of N for Yongyou 2640 was 18.33 kg kg-1,20.89 kg kg-1,23.26 kg kg-1,24.33 kg kg-1,19.83 kg kg-1 and 18.52 kg kg-1,respectively,under IDRN,PI,ACF,DP,ASZF,AEM,and increased by 32.54%,51.05%,68.19%,75.92%,43.38%and 33.91%,respectively,compared with that under the control.The value of Wuyunjing 24 was 14.26 kg kg-1,18 kg kg-1,19.37 kg kg-1,19.85 kg kg-1,17.03 kg kg-1,14.48 kg kg-1,respectively,under IDRN,PI,ACF,DP,ASZF,AEM,and increased by 21.57%,53.45%,65.13%,69.22%,45.18%and 23.44%,respectively,compared with that under the control.The internal NUE,physiological NUE,apparent recovery efficiency of N fertilizer,and partial factor productivity of applied N of the two varieties were significantly higher under IDRN,PI,ACF,DP,ASZF than under the control,with more significant under DP and ACF.Either DP or ACF included IDRN,PI and more application of N at the later growth stage.The results suggest that combination of DP or of ACF with IDRN,PI and more application of N at the later growth stage could synergistically increase grain yield and NUE.3.Canopy light and nitrogen distribution and biochemical mechanismCompared with the control(LFP),the cultivation patterns of IDRN,PI,ACF,DP,ASZF showed a smaller canopy extinction coefficient for light(KL)and larger canopy extinction coefficient for N(KN)and KN/KL,could better coordinate the distribution of light and N in the canopy,increase photosynthesis of leaves in upper,middle and low parts in the canopy,root oxidation activity,cytokinin accumulation in the flag leaf,and enhance activities of enzymes in upper leaves involved in nitrogen metabolism.Accordingly,these improved traits contributed to better regulation in N transport and distribution in the canopy,better matching between light and N in canopy,and eventually to an increase in photosynthetic efficiency of N in a rice canopy.