Instrument equipment and reagents:

1Fully automatic nitrogen analyzer SKD-1000 (Shanghai Peiou Analytical Instrument Co., Ltd.)

2Digestive Furnace SKD-20S2 (Shanghai Peiou Analytical Instrument Co., Ltd.)

3One ten thousandth scale

Standard sulfuric acid concentration: 0.01mol/L

40%Sodium hydroxide aqueous solution

2%A mixed indicator of boric acid, methyl red, and olfactory cresol green

Catalyst (a mixture of copper sulfate and potassium sulfate in a ratio of 1:10)

distilled water

The sample is a soil standard provided by Shanghai Fisheries Research Institute: 665mgN/KG(Allowable error ± 50mg)