We noticed methods of checking this loss, namely, pulverizing the soil with the tillage tools and putting organic matter into it to make it absorb the rain more readily.

We noticed that water poured on the sand ran through it very quickly and was apt to be lost by leaching or percolation.  This we found could be checked by rolling the soil and by putting organic matter into it to close the pores.

We learned that roots take water from the soil for the use of the plant and send it up to the leaves, which in turn send it out into the air, or transpire it, as this process is called.  We learned also that the amount transpired is very great.  Now water that is pumped up and transpired by the crops we are growing we consider properly used.  But when weeds grow with the crop and pump and transpire water we consider this water as lost or wasted.

Water may be lost then by being pumped up and transpired by weeds.  And this is the way weeds do their greatest injury to crops during dry weather.  The remedy is easily pointed out.  Kill the weeds or do not let them get a start.

There is another way, which we are not apt to notice, by which water may be lost from the soil.  When the soil in the pans in a previous experiment (page 26) had been wet and set aside a few days it became very dry.  How did the water get out of this soil?  That at the surface of the soil evaporated or was changed into vapor and passed into the air.  Then water from below the surface was pumped up by capillary force to take its place just as the water was pumped up in the tubes of soil.  This in turn was evaporated and the process repeated till all of the water in the soil had passed into the air.  Now this process is going on in the field whenever it is not raining or the ground is not frozen very hard.

Water then may be lost by evaporation.

How can we check this loss?

Suppose we try the experiment of covering the soil with some material that cannot pump water readily.

=Experiment.=—­Take four glass fruit jars, two-quart size, with straight sides.  If you cannot get them with straight sides cut off the tops with a hot iron just below the shoulder; tin pails will do if the glass jars cannot be had.  Fill these with moist soil from the field or garden, packing it till it is as hard as the unplowed or unspaded soil.  Leave one of them in this condition; from two of them remove an inch or two of soil and replace it in the case of one with clean, dry, coarse sand, and in the case of the other with chaff or straw cut into half-inch lengths.  Stir the soil in the fourth one to a depth of one inch, leaving it light and crumbly.  Now weigh the jars and set them aside.  Weigh each day for several days.  The four jars illustrated in Fig. 30 were prepared in this way and allowed to stand seven days.  In that time they lost the following amounts of water: 

Amounts of water lost from jars of prepared soil in seven days.