Moisture of the Soil. 483 



be rendered available. Few soils are so lacking in fertility that 

 they would not grow crops could the mineral plant food which 

 they contain be unlocked and brought into fit condition for use. 

 This important operation, as well as nitrification, — or the con- 

 version of nitrogen compounds into the form of nitrates, — can 

 proceed only in the presence of moisture. Crops plowed under 

 for green manuring, and barn manures, can be made available 

 only w^hen there is sufficient moisture in the soil to cause break- 

 ing down and decomposition. With moisture in the soil, there 

 is a constant movement towards the plant roots to restore the 

 equilibrium, or to make good that used by the plant. This move- 

 ment of the moisture brings to the roots the soluble plant food. 



The living root itself has the power of disintregating and 

 decomposing the particles of soil and of dissolving and extracting 

 some of the plant food. This powerful action, by w^hich the solid 

 rock is broken down and its plant food liberated and by which 

 even polished marble can be corroded, goes on only in the pres- 

 ence of moisture. Supply the plant with moisture, and its roots 

 are able to set free from the particles of the soil a part of the 

 mineral elements required for its growth. Supply even our 

 sandy desert plains with abundant moisture and immediately 

 they change from a desert to a garden. 



An acre of soil to the depth of one foot weighs approximately 

 1,800 tons. If 25 per cent, of this is moisture, we should have 

 450 tons of water per acre. An acre of soil to the depth of eight 

 inches weighs about 1,200 tons. If 25 per cent, of moisture were 

 found here it would contain per acre 300 tons of water. Plants 

 can maintain themselves with as low as 5 per cent, of water, 

 but their growth seems tO' go on most rapidly in soils whose 

 water content is from 13 to 25 per cent. 



The conservation or saving of moisture. 



The annual rainfall in New York is sufficient for the require- 

 ments of plants, could it be distributed or conserved during the 

 growing season. The experiments conducted by the U. S. Dept. 

 of Agriculture with a view to controlling the distribution of rain- 

 fall, proved that it was beyond control by any means known at 

 present. Dependence must then be placed upon irrigation or 



