FERTILIZATION AND FERTILIZERS 147 



Liming makes heavy clay or adobe soils easier to 

 work, also helps sandy soils to maintain crumb struc- 

 ture (tilth, see page 63) and to form humus. 



How to use fertilizers. The best fertilizers will be 

 of no use if the roots of the crops cannot reach them. 

 So, if we know that the roots in our land go deep and 

 do not stay near the surface, we must put the fertilizer 

 in deeply also. In humid regions it is usual to put 

 manures on the surface in autumn and let the winter 

 rains wash them partially into the soil before plowing 

 them in. If they are easily dissolved in water (as in 

 the case of Chile saltpeter and potash salts), they need 

 not be plowed in at all. This is because the roots of 

 crops in the humid region remain within a foot or two 

 of the surface. 



But in the arid region, where roots go very deep and 

 most of tEe time have no feeding roots near the sur- 

 face, all fertilizers except saltpeter and potash salts 

 (which are carried deep enough by rain or irrigation 

 water) should be put in deeply also, so that they may 

 nourish the roots during the growing season. 



Generally it is best to spread fertilizers evenly -over 

 the entire surface of the land, so as to favor the spread 

 of the roots all through the ground. Leaving stable 

 ^ manure in piles on the fields is bad practice. Young 

 trees are often at first fertilized in a small circle around 

 he trunk in order to push their growth; but this should 

 not be continued. When planting crops in rows or 



