| The rational application of nitrogen fertilizer under straw return conditions is one of the most important means to achieve stable and efficient crop yield.In order to clarify the optimal nitrogen application rate of spring maize varieties with different nitrogen efficiency under the condition of full straw return,and to explore the carbon and nitrogen metabolism mechanism of spring maize nitrogen reduction and efficiency improvement under the condition of straw return,four tillage measures were set up in this study:the nitrogen-efficient variety Xian Yu 335(XY335)and the nitrogen-efficient variety Nong Hua 101(NH101)as the experimental materials,and Four tillage measures were set up:farmer’s shallow rotational crop,no-till mulch return(NTR),deep pine straw mix and return(SSR),and deep-turned straw crushing and total return(DPR),and N3 normal N application(300 kg/hm~2),N2 15%N reduction(255 kg/hm~2),N1 30%N reduction(210kg/hm~2),N0 no N application(0 kg/hm~2),and four N application levels,with farmer’s shallow rotational crop and normal N application(300 kg/hm~2,N3)as CK.The study and analysis of carbon and nitrogen metabolites and key enzyme activities,photosynthetic characteristics,yield and nitrogen efficiency of different N-efficient varieties under different N application rates and straw reversion,clarified the response of N metabolism of spring maize to reduced N application under straw reversion,determined the appropriate N fertilizer application rates for different straw reversion methods,and revealed the effect of reduced N fertilizer application on N fertilization under straw reversion from the perspective of carbon and N metabolism.The physiological mechanisms of N fertilizer application on the stabilization and efficiency of spring maize with different N efficiency were revealed from the perspective of carbon and N metabolism,providing a theoretical basis for achieving high yield and efficiency of maize in Inner Mongolia.The main findings of the study are as follows:(1)Straw return to the field can improve the N fertilizer utilization rate of different N-efficient varieties,and the N fertilizer bias productivity,N fertilizer agronomic efficiency and N utilization rate among the return methods were DPR>SSR>NTR>CK,and DPR maintained higher N fertilizer utilization efficiency at 15%N reduction level even after successive years of straw return to the field.Under this level of nitrogen application,the nitrogen-efficient variety increased its nitrogen fertilizer bias productivity by 19.76%,nitrogen fertilizer agronomic efficiency by 12.65%and nitrogen utilization rate by 0.82%compared to CK;the nitrogen inefficient variety increased its nitrogen fertilizer bias productivity by 15.90%,nitrogen fertilizer agronomic efficiency by 2.87%and nitrogen utilization rate by 1.94%compared to CK.The potential to improve N fertiliser efficiency under straw return conditions is greater than that of N inefficient varieties.(2)Straw fertilisation with N fertiliser effectively improved the photosynthetic characteristics of N-efficient maize varieties,increasing the increase in leaf area,SPAD,net photosynthetic rate and dry matter mass per plant,and reducing the rate of decline in the later stages of fertility.Even at the late stage of spatulation when maize light and characteristics were significantly reduced,the advantage of straw return to the field was thrown significantly,with the strongest advantage of DPR,and the photosynthetic characteristics of N-efficient varieties under DPR treatment were all not significantly different from normal N application after 15%level of N reduction,while N-inefficient varieties decreased significantly.(3)Straw return to the field could effectively alleviate the reduction in carbon metabolites and key enzyme activities of different N-efficient maize varieties caused by the reduction of N fertilizer application at late reproductive stage.Sucrose,starch and total soluble sugar contents were significantly increased by 20.43%,30.18%and 25.24%,respectively,and sucrose phosphate synthase and sucrose synthase activities were significantly increased by 10.25%and 11.08%,respectively,in NH101 under DPR treatment with 15%N fertilizer reduction compared to CK.The organic carbon content of the N-efficient varieties was not significantly different from that of N3 at the N2 level,while the N-inefficient varieties showed a significant decrease of 7.30%.(4)The reduction in nitrogen metabolites and key enzyme activities of maize caused by the reduction in nitrogen fertilizer application at the late stage of fertility was effectively mitigated by the straw return,33.50%(free amino acids),11.72%(nitrogen accumulation),24.74%(nitrate reductase)and 37.71%(glutamine synthetase)compared to NH101.The N metabolites and key enzyme activities were increased to the greatest extent in the DPR treatment,and all the indicators of XY335 at the N2 level were not significantly different from those of N3.(5)The correlation analysis among carbon and nitrogen metabolites,key enzyme activities,plant photosynthesis and yield indicators of different N-efficient varieties at 30d in straw return conditions were all positively correlated,while the correlation coefficients among carbon and nitrogen ratio,N efficiency and yield indicators were all negatively correlated,with higher correlation coefficients for N-efficient varieties than for N-inefficient varieties;the highest correlation coefficients were found for DPR under different return conditions.(6)The best economic N application rate of different varieties could be effectively reduced by returning the straw to the field in full in successive years.the best economic N application rate under DPR treatment was 256.55 kg/hm~2on average for N-efficient varieties and 293.54 kg/hm~2for N-inefficient varieties.the best N application rate of N-efficient varieties was 12.60%lower than that of N-inefficient varieties,and the yield was increased by 7.46%. |
PDF Full Text Request