24 The Coeorado Experiment Station. 
use the larger sizes. Where cut seed is used, as is most commonly 
the case, the pieces should contain one or two good eyes each, and 
should be large enough to. nourish the young plant until it takes 
hold of the soil. The growth of the young plant from germination 
until a root system is formed is dependent entirely on the stored 
food contained in the seed piece. 
Cultivation .—Cultivation should begin soon after the crop is 
planted—sometimes before the plants are up. The soil becomes 
packed during planting, and immediate cultivation is advisable in 
order to conserve moisture and aerate the soil. 
Before the crop is up the ground should be well harrowed with 
a spike-tooth harrow. This may be profitably repeated after the 
plants are well up, and without any injury to the growing crop. 
The next two cultivations should be deep, and close to the rows. 
This leaves a loose medium for the potatoes to grow in. After 
this, surface cultivation which keeps down weeds and maintains a 
soil mulch, should be the rule. 
Irrigation .—It is usually unnecessary to irrigate during the 
early stages of the crop, as there is enough rainfall, ordinarily, to 
cause the seed to germinate and bring the plants to the stage where 
the tubers begin to form. From then until about the time the crop 
matures, irrigation is necessary. The number of irrigations needed 
will, of course, vary with the weather conditions. The general ten¬ 
dency seems to be to give too much, rather than too little water. 
The water may be allowed to run down every other furrow the 
first irrigation and down alternate furrows the next time. 
In dry seasons, however, it will be necessary to apply water to 
get the plants up. When this is the case, the water should be run 
in a furrow a few inches from the row and allowed to soak through 
to the soil around the seed. After that, it will probably not be nec¬ 
essary to irrigate again until the potatoes commence to form. As 
soon as the surface soil is dry enough, after each irrigation, it 
should be cultivated in order to check evaporation. 
It is sometimes necessary with varieties which set their tubers 
shallow, to employ protective ditching, by which soil is thrown over 
the hills, in order to protect the potatoes from frost. This is ac¬ 
complished by running through the middles some implement which 
makes a narrow, straight-sided ditch, throwing the soil from the 
ditch over the hills. Of course, none of the tubers must be dis¬ 
turbed by this operation. 
Harvesting .—The dates after which it is dangerous to leave 
potatoes in the ground vary with the altitude, from October ist to 
