270 PLANT BIOCHEMISTRY 



be accounted for by its content of the three principal fertilizer ele- 

 ments, nitrogen, phosphorus, and potassium. 



Composition of farm manure. Fresh farm manure consists of solid 

 and liquid components, the former approximating 75 per cent and the 

 latter 25 per cent of the total weight. As a rule about one-half the 

 nitrogen and potassium and nearly all the phosphorus are found in 

 the solid portion. The feces may contain a considerable amount of 

 undigested matter in the form of the original compounds of the ration. 

 However, the urine does not contain undigested feed but contains 

 waste products from the organs and tissues of the body. The com- 

 pounds eaten by animals are hydrolyzed in the alimentary tract 

 through the action of digestive or bacterial enzymes. As a result much 

 of the fresh excrement consists of compounds less complex than the 

 compounds ingested. The manvne as voided contains numerous 

 microbial species, including fungi, actinomycetes, and, particularly, 

 bacteria. A relatively large part of the total weight of manure con- 

 sists of the bodies of living and dead bacteria. The most resistant con- 

 stituents of feedstuffs, from the standpoint of digestibility, are the 

 various plant lignins, although considerable quantities of cellulose and 

 hemicellulose also escape digestion. In the intestinal tracts of animals 

 lignin combines with proteins (chiefly bacterial proteins) to form 

 lignoprotein complexes, called humus. The humus of manure ap- 

 parently is identical with the humus which is found in soils. It has been 

 estimated that 25 per cent of the organic matter of cow manure is 

 humus. 



The composition of fresh or decomposed manure varies greatly and 

 can be only approximately stated. Its content of N, P, and K is com- 

 parable to that of a low-analysis fertilizer and may not exceed 0.5 per 

 cent N, 0.25 per cent PoO-,, and 0.5 per cent KoO. Only about one- 

 half the nitrogen and potassium and about one-sixth the phosphorus 

 are readily available to plants. Since the phosphorus is present in 

 smallest amount and is less available than the other elements, it is 

 evident that manure is not a balanced fertilizer and should be sup- 

 plemented with a source of phosphorus. The amount of phosphate 

 fertilizers that should be added to a ton of manure depends upon the 

 acre-rate of application of the latter. If 10 tons is to be spread on an 

 acre of land, each ton should be re-enforced with at least 50 lb. of 20 

 per cent superphosphate. 



In addition to nitrogen, phosphorus, and potassium, manure con- 

 tains substantial amounts of calcium, magnesium, and sulfur, and 

 varying amounts of the micronutrient elements. 



The factors that influence the composition of farm manure include 



