Effect of N application on nitrate accumulation and nitrogen recovery ratio in grass forage

A pot experiment was conducted to investigate the effects of different N applied rates(100,200,300,and 400 kg/hm2) on nitrate accumulation in leaves and roots,protein content in stems and leaves,and the N utilization rates by pennisetum americanum×P.purpureum and Euchlaena mexicana during different growing stages.There was a positive correlation between the leaf nitrate content of the two forages and N application rate,but N rates had no significant influence on root nitrate content.With growth of the forages,leaf nitrate content increased slightly,and root nitrate content rose at first then declined,but the nitrate contents of the forages during all stages of this experiment were below the poisonous limit of 0.25%.The DMPE,CPPE and NARR contents of the two forages diminished with increased N application but protein content showed an upward tendency with the highest protein contents of P.americanum×P.purpureum and of E.mexicanna reaching 23.23% and 25.80% respectively.This means that N utilization rates decreased with increased N application rates,resulting in a gradual decrease of the protein content with growth of the forages.In a comprehensive assessment,the recommended dose of fertilizer N for P.americanum×P.purpureum and E.mexicanna was 200 kg/hm2 in hilly areas of red soil.