Effect Of Nitrogen Application Under Salt Stress On Physiological And Biochemical Characteristics And Quality Of Forage Rapeseed

Object:Soil salinization,as one of the major bottlenecks limiting sustainable agricultural development,can cause ionic toxicity and physiological drought to crops,disrupting their normal metabolism and thus affecting their yield and quality.Nitrogen is the most demanded element among essential nutrients in crops,which not only actively participates in a variety of physiological metabolic activities in crops,but also promotes crop growth and development,relieves stress,and ensures high and excellent crop yield.Soil salinization is common in Xinjiang,and the problem of winter forage shortage in animal husbandry is prominent.Forage rape has the advantages of short reproductive period,high biomass and high nutritional value,and exploring the cultivation of high-quality forage rape in saline land can provide new ideas to alleviate the shortage of overwintering forage for animal husbandry and the synergistic development of animal husbandry in agricultural areas.Based on this,this study analyzed the physiological and biochemical response characteristics of applied nitrogen on the growth and development,nitrogen accumulation and alleviation of salt stress in oilseed rape,clarified the effect of nitrogen on the quality of forage oilseed rape under salt stress conditions,and provided a theoretical basis for the rational application of nitrogen fertilizer to forage oilseed rape and the improvement of salt tolerance in forage oilseed rape.Methods:The experiment was conducted with“Hua You Za No.62”as the test material,and the two factors of sodium chloride（Na Cl）and nitrogen application were added outside the pot setting,and the amount of Na Cl added was 0（S₀）,3.5（S₁）,5.5（S₂）,7.5（S₃）g·kg^-1;the amount of nitrogen（pure N）were added at 0（N₀）,0.15（N₁）,0.3（N₂）and 0.45（N₃）g·kg^-1 for 16 treatments,with 10 replicates for each treatment.The growth index,physiological index,photosynthetic index and quality index of forage rape were measured at seedling stage,bud stage,early flowering stage and full flowering stage,and the nitrogen utilization efficiency of forage rape was measured at full flowering stage.Results:（1）With the increase of salt content,the water content,plant height,dry matter accumulation,nitrogen concentration in different parts and nitrogen utilization rate of forage rape decreased,so that the growth and development of rape were hindered;with the increase of nitrogen application,the plant height,dry matter accumulation and nitrogen concentration in different parts of forage rape increased significantly,and the water content and nitrogen utilization rate showed a trend of first increasing and then decreasing.As fertility progressed,dry matter accumulation and plant height gradually increased,water content showed a trend of first increasing and then decreasing,and nitrogen concentration in different parts gradually decreased.（2）With the increase of salt content,MDA,relative conductivity and Na⁺content increased and SS and K⁺content decreased significantly in forage rape;after the application of nitrogen,the activities of enzymes POD,SOD and CAT in ROS scavenging system showed a trend of increasing and then decreasing with the increase of nitrogen application,while the contents of non-enzymes ASA,GSH and Car continued to increase;SP,SS and K⁺in osmoregulatory system showed a trend of increasing and then decreasing,while Pro content gradually accumulated.Correlation analysis showed that there were highly significant correlations between different physiological indicators of ROS scavenging system and osmoregulatory system（ROS scavenging system with Pro,Na⁺and K⁺,enzyme system with SP,etc.）.（3）With the increase of salt content,photosynthesis of forage rape was hindered,and after the application of nitrogen,the content of photosynthetic pigments（Chl_a,Chl_b and Chl）in forage rape leaves gradually increased with the increase of nitrogen application;P_n,g_s and T_r showed a trend of increasing and then decreasing,while C_i showed a trend of decreasing and then increasing;q P,ΦPSII,F_v/F_m and F_v/F₀continued to increase,while NPQ continued to decrease.Correlation analysis showed that different physiological indicators were significantly correlated with photosynthetic indicators（enzyme system,ASA and SS with chlorophyll,K⁺with gas exchange parameters,SS with chlorophyll fluorescence kinetic parameters,etc.）within both the ROS scavenging system and the osmoregulatory system.（4）The high salt treatment reduced the quality of forage rape,crude protein,starch and crude fat content decreased with increasing salt content,while crude ash,acidic detergent fiber and neutral detergent fiber content showed an increasing trend.The application of nitrogen under salt stress significantly improved the quality of rapeseed.Crude fat and crude protein content increased with the increase of nitrogen application,and starch content showed a trend of first increasing and then decreasing;crude ash,acidic detergent fiber and neutral detergent fiber content showed a trend of first decreasing and then increasing,and excessive application of nitrogen would affect the quality of rapeseed to decrease.As fertility progressed,crude protein and crude fat content were highest at first flowering,acidic detergent fiber and neutral detergent fiber were lowest,and starch content was highest and crude ash was lowest at full flowering.Conclusion:With the increase of soil salt content,the growth and development,dry matter accumulation and forage quality of forage oilseed rape decreased significantly.Suitable nitrogen application can improve the rate of ROS scavenging in forage oilseed rape,maintain the osmotic balance inside and outside the cell and promote photosynthesis,enhance salt tolerance,alleviate the harm caused by salt stress throughosmoregulation,ROS scavenging and photosynthetic synergy,and improve the quality of forage oilseed rape.