512 



the quantity and quality of residues of croi)S returned to soil after the 

 harvest. The latter is considered by the author the main point in 

 question, and in this connection cites the results of the observations of 

 M. Weiske, as follows : 



Cro^s leaving residue upon the soil. 



On comparison of the figures found in the above table, we find that 

 the residue from the 'crop of clover will furnish enough nitrogen to sat- 

 isfy the demands of a crop of wheat producing about 283 bushels per 

 hectare,* and phosphoric acid sufficient for 227 bushels ; the crop of 

 lucerne leaves enough of nitrogen for a crop of 227 bushels, and of phos- 

 I)horic acid, for 113.5 bushels. The wheat and barley would, however, 

 leave sufficient for only 28 bushels. The difference in the value of these 

 crops for the purj^oses mentioned is very evident, since it appears that the 

 leguminous crops leave in a favorable condition for assimilating enough 

 of fertilizing materials to satisfy the demands of several crops of cereals ; 

 while in case of cereal crops nearly all of the elements of plant-food are 

 carried off in the grain. 



In favor of leguminous plants for green manuring, the author advances 

 the idea that besides carrying into the soil these mineral elements of 

 plant-food, they also supply to the soil an amount of moisture corre- 

 sponding to a rain-fall of about three millimeters, or about 0.12 inch. 

 The moisture received by the soil in this way affords an advantage over 

 that supplied by the rain in that it is not so rapidly dissipated by evap- 

 oration. 



In conclusion he considers that the explanation of the good effects of 

 the so-called ameliorating crops does not depend upon any special faculty 

 possessed by certain plants to assimilate atmospheric nitrogen ', that 

 this ameliorating property cannot be taken in an absolute sense, since 

 all plants diminish rather than increase the quantity of materials for 

 X)lantfood in the soil ; that an ameliorating culture should be defined 

 as one which yields to the soil residues, which, by their quantity and 

 quality, may favor the demands of subsequent crops ; that the quantity 

 and quality of the residues of green i^lants are more favorable than those 

 of dead plants; that it is therefore unadvisable to wait for the death of a 

 crop of clover or lucerne before changing the culture ; that the useful- 

 ness of a meadow in rotation and plowing under green vegetation may 

 be explained by the power displayed by each plant to seek, choose, 

 assimilate, and accumulate valuable materials which may be returned 

 to the soil in a readily assimilable form; that plowing under green veg- 

 etation, as well as fertilizers, should be specialized according to the 

 subsequent crop* 



* 2.47 acres. 



