472 AMNUAL, KEPOKT OF TilK Off. Doc. 



the effect of the lime is to cement the particles together and make 

 the soil more compact, which increases its absorptive properties 

 and a consequently greater retention in and utilization of the food 

 in the soil by the plant. 



The third function of lime, in to neutralize any acid that may be 

 present in the soil, and which not only injuriously affects the growth 

 of certain kinds of plants, but which is destructive to the life and 

 growth of many of the lower organisms. Naturally this function 

 of lime will be exerted whenever the lime is used for the other 

 purposes mentioned, still there are cases where it would be desira- 

 ble to use it only for this purpose, in which case the application 

 may be much less. The advantage of lime in the growth of legumi- 

 nous crops, for example, is not altogether because of the fact that 

 this class of plants requires an abundance of lime, but because the 

 lime exercises a favorable influence upon the physical character of 

 a soil, besides making it neutral, and thus a better medium for the 

 growth and development of the soil organisms, which have the 

 power of gathering nitrogen from the air and which cannot thrive 

 without air or in an acid medium. 



The Importance of Vegetable Matter. 



The lines of practice which have been suggested, in order both 

 to prevent losses from soils and to improve their physical character, 

 namely, the continuous cropping system, which holds fast to the 

 available food in the soil, liable to be lost when the land is uncropped, 

 and the addition of amendments which assist in making the neces- 

 sary changes, also includes the further advantage of adding to the 

 soil that which it did not before possess, viz: vegetable matter, 

 or humus-forming material, which also improves the soil, not only 

 in its absorptive properties for both moisture and plant food, but 

 which contributes to the store of active essential constituents. The 

 various crops that may be used to attain the first mentioned pur- 

 pose, however, do not possess an equal value in this respect, and 

 unless the principles which govern and the conditions under which 

 they are grown, as well as the influence of the crops grown upon 

 future productivity are well known the results obtained may not 

 be always satisfactory. 



Kind of Crops to Grow. 



In the first place, the crops that may be used are divided into two 

 distinct groups, in one group are included those plants which can 

 obtain the necessary nitrogen for their growth only from soil sources 

 and called ^'nitrogen consumers," and, therefore, when plowed down 

 do not add to the soil any essential constituent element and are only 



