THi: roXTENTS OK TIIK SOIL 21 



friabl«> soil ricli in vcgotabh' mattci*, the original 

 l»asis of which is san«l ; a clay loam is one simi- 

 larly amclioratctl, the Ijasis of which is clay. 

 "Worn-out" lands usually suffer more from 

 lack of hunms ihan fi-oni lack of actual ]»hint- 

 food, and this explains why the apjilication of 

 stable-manure is so eHicaci(»us. 



'M. There are three general ways in which 

 hunms is obtained in farm-i)ractice : (1) By 

 means of the vegetable matt<'r which is left on 

 or in the ground after the crop is rcnio\rd (as 

 r(3ots, stubbl(>, si»d, gar<it'ii i-cfuse); (2) by 

 means of cr«»i»s grown and jdowed un<ler for 

 that particular purpose (grecn-manui'ing) ; (.*]) by 

 means of dire<'t ajiplications to the land (as com- 

 post and stable-manure). The deeper and nioic 

 extensiv<» the root-system of any i>lan!, the 

 greater, in general, is its value as an ameliorator 

 of soil, both be<'ause it itself exerts a nioie wide- 

 spread inlluence (.'!()), and because when it de- 

 cays it ext<'nds tlie ameliorating e<Teet< ..f hunms 

 to greater depths. 



.'J."). Aside from these x.nied coinpoiinit ele- 

 ments, fertile soil is inhabited by countless nmn- 

 bers of micr«»seopic oriranisms, which are peculiar 

 to it, and without which its various chemical 

 activities can not proceed. These germs con- 

 tribute to the breaking <lown of the soil particles 

 and to the decay of the organi«" mat«'rials, and 



