The sources of nitrogen in the soil generally have the following aspects: chemical nitrogen fertilizers and organic fertilizers applied to the soil, the return of animal and plant residues, biological nitrogen fixation, lightning rainfall, etc. At present, the fertilizer applied to the soil is the main source of soil nitrogen. Today, P. Lihui Biology has sorted out how to determine soil hydrolyzed nitrogen by alkali diffusion method:
1. Reagents
(1) 1.0mol/L sodium hydroxide solution: Weigh 40 g of chemically pure sodium hydroxide, dissolve it with distilled water and cool it to a fixed capacity of 1000 ml.
(2) 1.2mol/L sodium hydroxide solution: Weigh 48 g of chemically pure sodium hydroxide and dissolve it with distilled water to 1000 ml.
(3) 1.8mol/L sodium hydroxide solution: Weigh chemically pure sodium hydroxide 72 g, dissolve with distilled water and cool to a capacity of 1000 ml.
(4) 2% boric acid solution: weigh 20 g of boric acid, dissolve with hot distilled water (about 60 ° C), dilute to 1000 ml after cooling, adjust the pH to 4.5 with dilute hydrochloric acid or dilute sodium hydroxide (nitrogen mixture indicator shows wine red).
(5) 0.005mol/L (1/2 H2SO4) sulfuric acid standard solution: take the amount of H2SO4 2.83 mL, dilute it to 5000 mL with distilled water, and then calibrate it with standard alkali or boric acid, which is 0.0200mol/L (1/2 H2SO4) standard solution, and then accurately dilute this standard solution by 4 times to obtain a standard solution of 0.0050mol/L (1/2 H2SO4).
(6) Nitrogen mixed indicator: 0.5 g bromocresol green and 0.1 g methyl red dissolved in 100 ml ethanol.
(7) Special glue: gum arabic (weigh 40g of powdered gum, dissolved in 50 ml distilled water) in a beaker warm to 70-80 ° C, stirring to promote solubilization, about 1 hour after cooling. Add 20 mL of glycerol, 20 mL of saturated aqueous potassium carbonate solution, stir and let cool. Centrifuge to remove foam and insoluble matter, and store the clear liquid in a stoppered glass bottle for later use. (Preferably placed in a dryer containing concentrated sulfuric acid to remove ammonia)
(8) Ferrous sulfate (powdered): The analysis of pure ferrous sulfate mill is stored in a cool and dry place.
Second, the main instruments
Diffusion dish, microtiter, 1/1000 analytical balance, incubator, glass rod, ground glass, leather band, straw (2 ml and 10 ml), waxed paper, corner spoon, porcelain dish.
Third, the preparation of the specimen
Weigh 2.000 g (accurate to 0.001 g) and 1 g of ferrous sulfate powder by air-dried by sieve No. 18 (pore size 1 mm), spread evenly in the outer chamber of the diffusion dish, and gently rotate the diffusion dish horizontally to flatten the sample. (Paddy soil samples do not have to add ferrous sulfate.) )
Fourth, the analysis steps
1. Aspirate 2 ml of 2% boric acid solution with a straw, add to the inner chamber of the diffusion dish, and add 1 titration nitrogen mixture indicator dropwise, then coat the edge of the outer chamber of the dish with special glue, cover the ground glass, and rotate several times so that the ground glass is completely bonded to the edge of the dish, and then slowly turn the side of the ground glass, so that the diffusion dish exposes a slit, quickly add 10 ml of 1.8 mol/L sodium hydroxide to the outer chamber of the dish with a pipette (paddy soil samples add 10 ml of 1.2 mol/L sodium hydroxide), and immediately cover it with frosted glass.
2. Gently rotate the diffusion dish horizontally so that the alkali solution is well mixed with the soil, fixed with a rubber band, labeled, and then placed in a 40 °C incubator. After 24 hours, remove, and then titrate the amount of nitrogen absorbed in the inner chamber with a micro-burette in 0.01 mol/L HCl standard solution, and the solution is dripped from blue to slightly red as the end point, and the amount of hydrochloric acid is written down to the number V of ml. At the same time, a blank test is done, and the amount of hydrochloric acid used for titration is V0.
5. Calculation of results
where:
Molar concentration of C-0.005mol/L (1/2 H2SO4) standard sulfuric acid;
V—the number of milliliters of hydrochloric acid used to titrate the sample;
b—the number of milliliters of standard hydrochloric acid consumed by the blank test;
m—initial sample weight;
14—Molar mass mg/mol of nitrogen atoms;
1000—Converted to the number of mg of nitrogen per 100 g sample.
Source: Chengdu Baihui Biological Finishing