398 PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE. 



Rate of Humification of Green Manure. 



R. H. Carr 



Since the use of green manures is becoming a more common aid in main- 

 taining the fertility of the soil, many questions have arisen regarding the 

 availability of the plant food they contain as compared with that of foods in 

 artificial manures, farm manures, etc. Another question concerns the pos- 

 sible acidity of the soil produced by fermentation of manures turned under 

 when in a very green condition. The writer first became interested in the 

 acidity side of green manures on noting the different results in crop yield in 

 two parts of a 14 acre clover field. About one half of the field had been 

 plowed when the crop was green. The inner half had been plowed after the 

 crop had been left to ripen for seed. Then the whole field was put in wheat . 

 The wheat and clover were a failure on the outer half, but the inner half 

 produced 22 bushels to the acre and also a good stand of clover was secured. 

 Several years passed before a good stand of clover on the outer part of the 

 field was obtained. Hence it was thought the soil had been soured by the 

 large amount of green manure turned under. A number of writers comment 

 on the possiblity of souring the soil by the use of green manures. In circular 

 10 of Iowa Experiment Station is found the following statement regarding 

 green manures: 



"In its (organic matter) decomposition, acids may be in'oduced in con- 

 siderable amounts and the soil becomes acid or sour in redaction." 

 Ohjkct of Expkrimknt 



The object of this experiment was first, to determine th(* rate of decomp- 

 osition as measured !)>■ the rate of humification and growth of crops, second, 

 to determine the amount of acid formed wiieti (lilTereiit green manures de- 

 compose. 



Plan Followed 



Clay soil that was verj' deficient in organic matter, or luinuis hungry, 

 was chosen for the experiment. The soil was placed in boxes holding ap- 

 jn'oximately a cubic foot and was mixed with diffcrciil green or dry manures 

 as follows: 



Box 1, green cow pea stalks ;i, 000 grams, chopped up, well mixed with soil. 

 Box 2, green cow pea stalks H.OOO gi'ams, layer in middle of })ox, soil above 



and below. 

 Box 8, green cow pea stalks '.i,()(]0 grams, layer in middle of box lined with 



100 grams CaCos. 

 Box 4, green alfalfa 2,250 grams, layer in middle of box and 100 grains 



ca CO3 and soil. 

 Box 5, green alfalfa 2,2r)0 grams layer not limed plus soil. 

 Box (). green alfalfa 2,2.")0 grains, cho])ped and mixed willi soil. 



