136 Bulletin 394 



It has already been stated that no method has been devised which 

 will measure the rate of decay of organic matter thru all its stages, and 

 that none of the methods in use at the present time for studying this 

 problem are free from objections. The question arose as to whether a 

 more satisfactory method could be devised. In this connection it seemed 

 possible that some modification of the alkaline permanganate method as 

 devised by Jones (191 2) might be appHcable. In this method a sample 

 containing 50 milligrams of water-insoluble organic nitrogen is washed 

 free from soluble salts, and digested below the distillation point with a 

 definite amount of alkaline permanganate of definite strength for thirty 

 minutes. The temperature is then raised, and during the next sixty 

 minutes 95 cubic centimeters of the sample is distilled over into standard 

 acid. The nitrogen thus obtained is designated as active water-insoluble 

 nitrogen. It is considered to be that portion which will rapidly become 

 available for plant use. The method has demonstrated its value in 

 differentiating between high- and low-grade sources of nitrogen in com- 

 mercial fertilizers. Its disadvantages are that it is empirical and may 

 give varying results with different investigators. As regards its adapt- 

 ability to the determination of the availability of soil nitrogen, it seemed 

 possible that with a given soil and a given source of organic matter the 

 rate of decay might be indicated by the increasing amounts of ammonia 

 distilled from the permanganate solution. It seemed that if the manipu- 

 lations were carried out with exactness, results comparable with one another 

 might be obtained. The possibility was considered worthy of experiment. 



After a number of trials of the alkaline permanganate method, it was 

 found to be inapplicable to the purpose desired. A few of the results 

 obtained are given, because of their bearing in explaining the failtire 

 of the method. A sample of soil containing the prescribed amount of 

 organic nitrogen was treated according to the procedure outlined for a 

 fertilizer material. Similarly, a sample of plant material was examined. 

 Next, a composite sample of soil and plant material containing the 

 required amount of organic nitrogen was run. The active nitrogen 

 obtained was about 25 per cent below the theoretical amount on the 

 basis of the materials examined separately. Using a larger amount of 

 permanganate solution, the results were somewhat higher but still did 

 not equal the theoretical. Samples of soil 'were next examined with 

 varying amounts of the reagent. The following results were obtained: 



Amount of reagent Active nitrogen 



(cubic centimeters) (grams) 



100 (prescribed amount) 0.01876 



125 0.02072 



150 0.02310 



200 o . 02501 



248 



