The storage device for nitrogen-pressurized hydraulic fluid，which is used in closing the blowout preventers is called the（）.
自生固氮菌 free-living nitrogen fixing bacteria
氮同化作用 nitrogen assimilation
硝态氮 nitrate nitrogen
硝铵态氮肥 ammonium and nitrate nitrogen fertilizer
英译中（Translate）：biological nitrogen fixation（）
氮素有效性比率 nitrogen availability ratio
全氮 total nitrogen
酰胺态氮 amide nitrogen
有机氮库 organic nitrogen pool
