54 HINTS ON SOILS AND FERTILIZERS 
to a fertile soil, if maximum yields are to be 
expected. We must have a sufficient amount 
of moisture in the soil, because we have seen 
how the plant takes its food in the form of a 
weak solution. If this moisture is not present 
£& the soil, then, no matter how much plant 
food is present in the soil, it will be of little 
value to the plant, because it has to depend 
upon moisture to supply its food in a form in 
which it can utilize it. In s6me of the dry 
sections of the country, this moisture is sup¬ 
plied by means of irrigation, where certain wa¬ 
ter paths are provided, running down ^through 
the field at regular intervals. This furnishes 
the moisture necessary to dissolve the elements 
in the soil, so that the small rootlets of the 
plants can absorb the moisture containing the 
plant food. Many of our best crops are raised 
in these irrigated districts. Sometimes, how¬ 
ever, we find that we have too much moisture 
in the soil. This is especially true in low 
places. It then becomes necessary to drain the 
soil of this excess moisture, so that the spaces 
between the soil grains are not clogged with 
water, and that sufficient air may be present. 
It has been estimated that considerably over 
one-fifth of the land in this country, capable 
of being cultivated, needs drainage, and that 
in the near future all this land will be drained, 
to supply the ever-increasing demand of farm¬ 
ing-land. 
If the spaces between the soil particles are 
filled with water, it is obvious that air cannot 
be present in the soil. Strange as it may seem, 
a certain amount of air is essential in the soil, 
