680 PRINCIPLES OF SOIL MICROBIOLOGY 



the final products of the reaction: viz., carbon dioxide, ammonia or 

 nitrate. These are the easiest and most reliable methods; carbon diox- 

 ide is the end product of energy utilization and respiration of microorgan- 

 isms; NH 3 is the product of the nitrogen metabolism of microorganisms; 

 since some or all of the ammonia is rapidly oxidized in the soil to nitrates, 

 both ammonia and nitrates should be determined in the latter case. 

 (3) Methods for measuring the formation or accumulation of the less 

 readily decomposable organic materials in the soil, namely the so-called 

 "humus" and the related compounds. 



Decomposition of the various constituents of the organic matter added to 

 the soil. In view of the fact that the most important constituents of 

 natural organic materials added to the soil are the celluloses, pentosans, 

 lignins, proteins and their derivatives, fats, waxes, and the lower sac- 

 charides, the quantitative determination of these substances is sufficient 

 to indicate the course of transformation of the organic matter added. 

 The methods for making these determinations are described in another 

 chapter. However, these methods have to be modified for certain of 

 the complex natural organic materials, such as straw, corn stover, and 

 forest products. Organic matter or the soil containing it is dried to con- 

 stant weight, extracted with ether to remove the fats, waxes and resins. 

 The material is then treated with cold and hot water to remove the pro- 

 tein degradation products, the sugars and starches. This is followed by 

 alkali extraction (2 to 5 per cent NaOH, for forty-eight hours in the cold 

 or for thirty minutes at 15 pounds pressure), which removes the lignins, 

 proteins, and, in the case of soil, the humus-like substances. The pen- 

 tosans are determined in 1 gram of organic matter or in an aliquot portion 

 of soil by distilling with 12 per cent hydrochloric acid, until a pink 

 color is no longer given with aniline acetate paper, then precipitating as 

 phloroglucide. The cellulose can be determined 24 by treating a separate 

 portion of the soil (20 grams) at 98° to 100°C. in flowing steam for 72 

 hours (for straw and manure) or 192 hours (for sawdust and moss) 

 with 100 cc. of a solution which contains 80 grams NaHS0 3 and 200 cc. 

 normal HC1 per liter, in flasks with patent rubber clamp stoppers; 

 the material is filtered through hardened filter paper, then washed with 

 water till colorless, dried at 50°C, and extracted with Schweizer's 

 reagent, then precipitating the cellulose with hydrochloric acid, washing 

 and drying as usual. Instead of this procedure, the soil containing the 

 organic material may be extracted with ether, water, 2 per cent NaOH 



24 Bengtsson, N. Bestamming av inkrusterad cellulosa i jord. Meddl. f. 

 Centralanst. forsoksv. jordbruks. Bakt. Avd. No. 37. 1925. 



