GREEN-MANURES 543 



duction is dominant and the amount of the humous materials 

 increases. In the second stage, humus production and humus 

 destruction are more or less balanced, while in the third stage 

 humus destruction is in the ascendant. The amount of humus 

 is on the decrease in the latter stage. The length of these 

 stages will vary with the season, with soil conditions, 1 and 

 with the character of the crop turned under. Obviously, the 

 influence of decomposing green-manure on the chemical and 

 biological activities of the soil will vary as the decay cycle 

 progresses. In general, over one-half of the organic matter 

 of the average green-manure disappears during the first nine 

 months after application. 



313. Influence of decaying green-manure. — In the first 

 stage of decay, which should be a rapid one, many complex 

 compounds are generated along with carbon dioxide and other 

 simple products. The complex materials, which result partly 

 from protein decomposition and partly from the breaking 

 down of easily attacked carbohydrates, may be harmful to 

 ordinary crops. Germinating seeds and young plants are 

 especially susceptible, and detrimental influences are some- 

 times noticed immediately after the turning under of a green- 

 manure. Fred 2 found that the germination of oily seeds, 

 such as cotton and soybean, was much reduced. Starchy 

 seeds, such as maize, oats, and wheat, were little affected. The 

 germination of flax, hemp, mustard, and clover was some- 

 what reduced. An actual contact of the seed with the de- 

 caying material was usually necessary for serious damage. 

 The detrimental influence always occurred during the first 

 two or three weeks after the green-crop was turned under. 

 Obviously the more succulent the crop, the shorter will this 

 period be. 



1 Eussell, E. J., and Appleyard, A., The Influence of Soil Conditions 

 on the Decomposition of Organic Matter in the Soil; Jour. Agr. Sci., 

 Vol. VIII, Part 3, pp. 385-417, 1917. 



3 Fred, E. B., Relation of Green Manure to the Failure of Certain 

 Seedlings; Jour. Agr. Res., Vol. V, No. 25, pp. 1161-1176, Mar., 1916. 



