Effects Of Nitrogen Nutrition On Stoichiometric Traits And Production Performance Of Echinochloa Frumentacea Under Saline-alkali Stress

Carbon(C),nitrogen(N),phosphorus(P)and potassium(K)are essential elements for crop growth.Studying the stoichiometric characteristics of key elements such as C,N,P and K of crops is helpful to understand the adaptation law of crops to external environmental changes,and has important theoretical guiding significance for innovating water and fertilizer management technology to regulate crop production.Echinochloa frumentacea is a pioneer forage crop in saline-alkali land improvement.How to scientifically and reasonably fertilize to improve grass yield is the key research content in the cultivation and management of Echinochloa frumentacea in saline-alkali land.At present,the research on the cultivation and management of Echinochloa frumentacea mainly focuses on the introduction and cultivation,yield and quality,and salt tolerance evaluation,etc.There are few reports on the stoichiometry of Echinochloa frumentacea under salt and alkali stress.In this paper,the effects of NaCl and Na2SO4 salt stress at different concentrations(50 mmol·L-1,100 mmol·L-1,150 mmol·L-1)on the stoichiometry of Echinochloa frumentacea were studied by indoor hydroponics and outdoor plot experiments.Effects of different nitrogen types(urea,ammonium sulfate,urea+ammonium sulfate)and different ammonium nitrogen application rates(7500 kg·hm-2,15000 kg·hm-2,30000 kg·hm-2)on stoichiometry of Echinochloa frumentacea in saline-alkali land,The content of C,N,P,K,biomass,plant height,stem diameter and nutritional quality of Echinochloa frumentacea were analyzed and determined.The results showed that:1.The contents of C,N and P in the above-ground and underground parts of Echinochloa frumentacea first increased and then decreased with the increase of salt concentration,but the contents of K in the above-ground and underground parts showed different trends with the increase of salt concentration.No matter NaCl salt or Na2SO4 salt,the contents of C,N and P in above-ground and underground parts of Echinochloa frumentacea reached the maximum when the salt concentration was 50 mmol·L-1.The K content in the underground part of Echinochloa frumentacea increased gradually with the increase of salt concentration,and the K content in the above-ground part increased first and then decreased with the increase of salt concentration,and the K content in the above-ground part reached the maximum when the NaCl and Na2SO4 salt concentrations were 50 mmol·L-1.2.Echinochloa frumentacea C:N,C:P,C:K,N:P,N:K,K:P showed obvious response to salt stress of different concentrations,and the trend of change with the increase of salt concentration was different according to salt species.No matter NaCl salt or Na2SO4 salt,with the increase of salt concentration,C:N in the above-ground and underground parts of Echinochloa frumentacea decreased first and then increased,and C:K,N:P,N:K in the underground part increased first and then decreased.Under Na2SO4 salt stress,C:P,C:K increased with the increase of salt concentration,N:P,N:K,K:P increased first and then decreased.Under NaCl salt stress,above-ground C:P,N:P,K:P showed an increasing trend,and C:K,N:K showed an increasing trend first and then a decreasing trend.3.Different nitrogen fertilizer forms had significant effects on hay yield,contents of crude protein,crude fat,C,N,P,K and stoichiometry of Echinochloa frumentacea.Compared with urea and ammonium sulfate+ urea treatment,ammonium sulfate had the most significant promoting effect on the performance of Echinochloa frumentacea under the same amount of pure nitrogen.The values of C:N,C:P and C:K could be decreased and the values of N:P and N:K could be increased.4.Plant height,stem diameter,crude protein,crude fat and hay yield of Echinochloa frumentacea increased first and then decreased with the increase of ammonium sulfate dosage,and hay yield reached the highest when ammonium sulfate dosage was 7.5t·ha.With the increase of ammonium sulfate dosage,the C:N,C:P,N:P,K:P values of Echinochloa frumentacea showed a trend of decreasing first and then increasing,while the C:K and N:K values showed a trend of decreasing.In conclusion,N:P<14,N:K<2 of Echinochloa frumentacea under salt-alkali stress,indicating that the production performance of Echinochloa frumentacea under salt-alkali stress is mainly limited by N element.Reasonable application of nitrogen fertilizer was beneficial to the growth of millet seed in saline-alkali soil,and the application of ammonium nitrogen(ammonium sulfate)had the most obvious effect on increasing yield.The application of 7500 kg·hm-2 ammonium sulfate as is more conducive to the growth and development of Echinochloa frumentacea in saline-alkali land.