THE TEXTURE OP THE SOIL 43 



plant-food, and that the rock contains a most abundant supply 

 of potash and about half as much phosphoric acid as the good 

 bean soil. 



"All this, after all, is not surprising, when we come to think 

 of it. Every good farmer knows that a hard and lumpy soil 

 will not grow good crops, no matter how much plant-food it 

 may contain. A clay soil which has been producing good crops 

 for any number of years may be so seriously injured by one 

 injudicious plowing in a wet time as to ruin it for the grow- 

 ing of crops for two or three years. The injury lies in the 

 modification of its physical structure, not in the lessening of its 

 plant-food. A sandy soil may also be seriously impaired for 

 the growing of any crop if the humus, or decaying organic 

 matter, 'is allowed to burn out of it. It then becomes leachy, 

 it quickly loses its moisture, and it becomes excessively hot 

 in bright sunny weather. Similar remarks may be applied to 

 all soils. That is, the terture and structure or physical condition of 

 the antl is nearly always more important than its mere richness in 

 plant- food. 



" The first step in the enrichment of unproductive laud is 

 to improve its physical condition by means of careful and 

 thorough tillage, by the addition of humus, and, perhaps, by 

 under-drainage. It must first be put in stu-h condition that plants 

 an grow in it. After that, the addition of chemical fertilizers 

 may pay by giving additional or redundant growth." 



53a. Read Chapter ii. in King's "Soil." The following is 

 quoted from that work, p. 72: "Suppose we take a marble 

 exactly one inch in diameter. It will just slip inside a cube 

 one inch on a side, and will hold a film of water 3.1416 square 

 inches in area. But reduce the diameters of the marbles to one- 

 tenth of an inch, and at least 1,000 of them will be required to 

 fill the cubic inch, and their aggregate surface area will be 

 31.41G square inches. If, however, the diameters of these spheres 

 be reduced to one-hundredth of an inch, 1,000,000 of them 

 will be required to make a cubic inch, and their total surface 

 area will then be 314.16 square inches. Suppose, again, the soil 

 particles to have a diameter of one-thousandth of an inch. It 



