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五、土壤速效钾测定(一)方法原理:用硫酸钠浸提以置换土壤胶体中的速效钾。加入四苯硼钠,与土壤溶液中钾生成难溶的四苯硼钾混浊,其混浊度与钾含量在一定范围内呈正相关。(二)测定步骤:1.称土壤2克于试管中,加10毫升1N硫酸钠浸提液(酸性土应加0.1克碳酸钙以固定铁、铝),振摇20分钟后过滤。2.吸取2毫升滤液于比色管中,加2滴甲醛—EDTA混合掩蔽剂,再加8滴四苯硼钠,用力振摇,即显白色混浊。放置5分钟,与标准液比浊,定其含量。
Fifth, soil available potassium determination (A) Principle of the method: sodium sulfate leaching to replace the quick-acting potassium in soil colloids. Adding tetraphenyboron sodium, with soil potassium solution to generate insoluble tetraphenylboron potassium turbidity, the turbidity and potassium content within a certain range was positively correlated. (B) Determination steps: 1. Weigh 2 grams of soil in the test tube, add 10 ml of 1N sodium sulfate extract (acidic soil should be added 0.1 g of calcium carbonate to fix the iron, aluminum), shaken for 20 minutes and filtered. 2. Pipette 2 ml filtrate in the cuvette, add 2 drops of formaldehyde-EDTA mixed masking agent, add 8 drops of sodium tetraphenylborate and shake vigorously, which is obvious white turbidity. Place for 5 minutes, turbidity with the standard solution, set its content.