i8 
Colorado Experiment Station 
be in the ground previous to the irrigation. This process is com¬ 
monly called “irrigating up.” 
In the San Luis V?dley spring, seeding should always be prac¬ 
ticed. It is usually advisable to delay seeding until the latter part 
of April or early in May, as the soil is then warmer and the crop 
' 'will start up more vigorously if other conditions are right. 
' ? . ' Irrigating .—The first year, especially, care should be taken in 
watering. The object should be to make root rather than top de¬ 
velopment. To accomplish this there must be water in the subsur¬ 
face and subsoil, because the roots will not grow downward into a 
dry soil. 'Frequently very light irrigations will keep the crop grow¬ 
ing, but will riot tend to produce root deevlopment. Relatively 
heavy irrigations, followed by lighter ones, will tend to produce a 
heavy root growth. , 
One of the most serious dangers to alfalfa is winter killing or 
more properly, spring killing, due to the dry, cold windy springs. 
To reduce this danger, it is advisable to irrigate in late September 
or early October, so as to have some moisture in the ground upon 
the approach of winter. A crop so irrigated will start off vigorously 
in the spring. Irrigation should be suph as to keep the crop growing 
energetically thruout the season. When the spring is dry, early 
irrigation is necessary. Where considerable winter or spring preci¬ 
pitation has fallen so that abundant moisture is in the soil it is ad¬ 
visable to withhold the early spring irrigation because the water at 
. this season is exceedingly cold and will retard plant growth. 
Usually three cuttings may be obtained in a season, or two 
cuttings and enough later growth to make considerable pasture, 
the latter often amounting in value to more than half a cutting. 
For this amount of growth, two or three irrigations will ordinarily 
be sufficient. On new land which has not been irrigated previously 
or on land very deficient in vegetable matter, more than one and 
one-half acre 'feet of water will probably be needed to produce 
maximum crops. Under most other conditions, however, one and 
one-half acre-feet will probably be.“ ample to grow a maximum crop 
and may be found to be more than is absolutely necessary in the 
short seasons which prevail in these altitudes. Alfalfa will give 
heavier yields and will survive much longer if proper methods O'f 
surface application of water are followed. It will make better root 
development, and with better root development is capable of giving 
better 3n*elds. Sub-irrigation frequently used in the Valley holds 
stagnant water in contact with the subsoil for long periods. Al¬ 
falfa roots are killed out in such standing subsoil water, but they 
will grow to great depths in moist subsoils which do not have suf¬ 
ficient water to stagnate. 
