1918.] SOILS FERTILIZERS. 721 



Experiments on the formation of so-called humin acid in mixtures of leaves 

 with various organic substances showed that liguin, tannic acid, and albuminous 

 substances, and some vegetable oils are sources of humin acid, while cellulose, 

 starch, glucose, gum, and cork are not. The amount of humin acid was greatly 

 decreased by the elimination of substances soluble in water and alcohol from 

 decomposed vegetable remnants. More humin acid was washed into the soil 

 from steppe grass than from the same amount of forest litter. 



Papilionaceous plants gave only humin acid soluble in water. 



The decomposition of sweet clover (Melilotus alba) as a green manure 

 under greenhouse conditions, L. A. Maynakd {New York Cornell Sta. Bui. 

 S94 (1911), pp. 121-149, figs. S).— This reports the results of investigations con- 

 ducted during 1914 and 1916 relating to the use of sweet clover as a green- 

 manure crop, with special reference to the ability of the plant to gather nitro- 

 gen and the rate of decay of the plant when incorporated with the soil. Volusia 

 silt loam soil was employed in the experiments, the plants being grown in pots 

 in the greenhouse. The soil was inoculated with a pure culture of the sweet 

 clover organism. In one series of pots the lime requirement was satisfied by 

 the use of slaked lime, in a second series by finely ground limestone, while a 

 third series was left unlimed. Seed tested for germination showed a germina- 

 tion percentage after four days of from 28 to 32 for untreated seed, and of 

 from 95 to 98 for seed treated by the sulphuric-acid method described by Love 

 and Leighty (E. S. R., 27, p. .524). 



The investigations during 1914 comprised a study of the yield and composi- 

 tion of the sweet-clover pliint after a period of growth of 62, 89, and 118 days, 

 respectively, for both the limed and unlimed pots. Data are also presented on 

 the formation of nitrates in pots having the plants removed or turned under 

 after a growth of 89 and of 118 days for a four-month period. 



The 1914 results having indicated that the four-month period of growth gave 

 the best results from the standpoint of the amount of available green manure 

 produced, it was decided to grow the plants for that period in 1916 before turn- 

 ing them under. Data similar to that noted above are, therefore, presented for 

 plants grown 116 days. 



In discussing the results obtained statistical methods are employed so far as 

 possible with regard to the production of dry matter and nitrogen, percentage of 

 fiber, and rate of decay. 



Recognizing the desirability of repeating the experiments under field condi- 

 tions before drawing general conclusions, the author summarizes his studies as 

 follows : " These experiments show that sweet clover will make a satisfactory 

 growth for use as a green manure in three or four months on a worn-out soil, 

 provided the lime requirement is satisfied. When the crop is harvested at 

 either of these periods it compares favorably in nitrogen content with other 

 legumes, and sufficient fiber has not developed to inhibit rapid decay. Growing 

 the crop for the longer period does not result in an increased proportion of 

 fiber. 



" The plant responds readily to inoculation with the appropriate organism. 

 To secure a good stand the seed bed should be compact and treated seed should 

 be used. The use of treated seed is important also from the standpoint of 

 ecoDomy. Treating the seed with acid increases the percentage of germination 

 threefold, and seed so treated does not lose its increased germinating power for 

 at least ten months. Satisfying the lime requirement of the soil was found to 

 increase the yield 50 per cent for the crop grown four months. . . . 



" Sweet clover grown for three or four months decays rapidly when used as 

 green manure. It was found that in the limed pots sufficient nitrates had been 



