An applicability of Teorell's method (Biochem. Ztschr., 248 : 246,1932), a micro-analytical method for ammonia in blood to the soil extract was tested first, and the formation of ammonia in the paddy-field soil was followed up by using the said method, and found as follows : (1) NaBrO and HBr reagents should not be older than a week but their use immediately after their preparation should be avoided ; (2) the method is applicable to determine ammonia in (NH_4) SO_4,NH_4Cl, NH_4NO_3 solution ; (3) best quantity of sample to be used is 0.5-5.0 cc., judging from the experimental error ; (4) within pH 3.0-8.0 range, the method can be used ; (5) for the solution containing Ca, K, Mg, Fe, SO_4,PO_4 and NO_3 ions, the soil water extract and putrefied solution of manures, the method is applicable ; (6) by using the method, the change of NH_3-N of ammonium sulfate, fish cake, soy-bean cake, fresh and ripened compost straw in the soil, was determined for thirteen weeks and found : (a) a large quantity of NH_3-N was found at an early period in all cases and decreases rapidly with the time, and after six weeks it becomes Practically constant viz. 1-2 mg. NH_3-N ; (b) the presence of various organic matter has no marked influence on the NH_3-N of ammonium sulfate, and the decompositin of soybean cake and fish cake is rather slow.
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