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All this prolific growth is made possible by the extreme heat of the summer months aided in the case of those plants and trees which flourish in the fertile soil of Ha Va Su by the sub-irrigation and the spray from the fall. After making an inventory of our provisions we concluded not to try the tedious and uncertain trip up Cataract Creek.
I suppose it sounds odd to hear desert and river in the same breath, but within a few feet of the river the desert begins, where nothing grows but sage and greasewood. In oasis-like spots will be found plenty of grass where the soil is nearer the surface and where sub-irrigation keeps the roots watered. In one of these spots the herd was being held.
The whole system should be laid deep enough in the ground to be secure from frost; but to be most effective it should not be over fourteen to sixteen inches below the surface, hence sub-irrigation cannot be used very successfully in the Northern states. In a sandy loam soil with a clay subsoil it works best at sixteen to twenty-four inches.
With a system of sub-irrigation pipes which deliver foul matters into earth that is subject to the active operation of oxidizing influences, we need fear no contamination of the deep and unaërated soil. It would be better, however, where this system is used for the disposal of the outflow of soil-pipes, to avoid the use of wells.
Every farm has a series of big ditches, three to six feet wide and about five feet deep, running across it. The water is drained off the land with tile into these ditches, but on the other hand these ditches provide with the aforesaid tile a form of sub-irrigation inasmuch as the water in the dry season flows back into the sub-soil through these same tile.
So far as village sewage is concerned, there are three means open for its disposal: to discharge it into running water or into deep tide-water, to use it for the surface irrigation of land, or to distribute it through sub-irrigation pipes placed at little distance below the surface of the soil.
The hill-side, immediately below the gutter, is brought to a true grade and covered with grass. As its inclination is much greater than would be admissible for sub-irrigation drains, these are laid obliquely in parallel lines at intervals of six feet from one end to the other over the whole graded slope.
The arrangement of the sub-irrigation pipes is easily made: Suppose that in land having an inclination of about one in two hundred, occupied by grass or other growth, a trench be dug twelve inches deep, that there be laid upon the bottom of this trench a narrow strip of plank to insure a uniform grade, and that upon this plank is laid a line of common agricultural land-drain tiles, say two inches in diameter.
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