Making A Ton of Hay!
And now for an interesting tidbit about alfalfa production! A ton of hay requires 4 to 5 inches of water pumped through the plant. Typically, in a three cut management system, 35-45% of the yield is produced during the first growth cycle, before July 1. The second growth cycle will produce 30-35% of the yield, while the third growth cycle will produce the remaining yield. The yield of the second cut is limited by the hot, dry weather, while the yield of the third cut is limited by growing season, decreasing heat units, and day length.
So, if each ton of alfalfa hay requires 4 to 5 inches of water, the alfalfa crop will need 12 inches for a 3 ton yield in the first cut. Assuming you can start with a moist soil depth of three feet at the beginning of the season, two 3" irrigations, spaced two weeks apart (June 1 and June 15), is a good start. Immediately after the first cut, apply 6" of water. Wait three weeks and apply three inches of water. Immediately after the second harvest, apply 6 inches of water. Wait three weeks and apply three inches of water. In total, you should have applied 24 inches (two acre feet) of water. You removed an additional 3-6 inches of water from the soil. Total water (not counting rainfall during the season) was 27-30 inches. At a water use requirement of 5 inches per ton, this would provide the water for a 6 ton per acre crop, assuming good fertility and no loss to weevils or grasshoppers.