ia6 Bulletin 394 



(19 14) has been referred to. These investigators studied the rate of 

 decay of sann hemp, using the accumulation of nitrates as the measure. 

 The plants were turned under at different stages of growth. The per- 

 centage of nitrification was found to decrease markedly with age. 



The work of the last-named investigators, together with that of Hill, 

 ■ shows the application of the study of nitrate formation to the problem 

 of the rate of decay of a green manure. The method is open to several 

 objections, but so are the other methods devised. The process of nitrate 

 formation is very sensitive to soil and atmospheric conditions, but this 

 objection to the method is less serious in pot experiments in the green- 

 house, where conditions can be carefully controlled and no nitrates are 

 lost by leaching. 



In the present investigation the crude-fiber content of sweet clover 

 was considered. It is believed that the amount of carbohydrate material 

 present has a bearing on the rate of decay. Hill (191 5) found that pure 

 cellulose and paper retarded nitrification. Paterson and Scott (19 12) 

 found that starch and sugar retarded nitrification. Hutchinson and 

 Milligan (19 14) state that the rate of decay of plant material depends 

 on the percentage of vascular ring and lignified parts. Brown and 

 Allison (19 16) found that straw did not increase nitrification as much 

 as did green manures; however, they found no relation between the 

 nitrogen-carbon ratio and nitrification. Wright (19 15) found that plow- 

 ing under materials such as old hay, leaves, and strawy manure, and 

 even green manure which had become dry, reduced the quantity of 

 available nitrogen in the soil. It appears that crops at later stages of 

 growth decay less rapidly, not only because they contain more fiber but 

 also because they contain less water. 



EXPERIMENTAL WORK 



The experimental work described in this paper extended over two 

 seasons. In 1914 a general study was made of crop yield and rate of 

 decay at different stages of growth and under different conditions as 

 regards liming. In 19 16 a further study was made of the period of 

 growth which seemed most desirable on the basis of the results obtained 

 the previous season. 



SOIL USED 



The soil used in the experiments was classified by the United States 

 Bureau of Soils as Volusia silt loam. The Volusia series occupy an 

 estimated area of about 10,000,000 acres in the United States, principally 

 in New York, Ohio, Indiana, and Pennsylvania. These soils occur 

 in New York State to the extent of over 20 per cent of the total area, 

 comprising about 35 per cent of the tillable land. Regarding the general 



238 



