IRRIGATION AND DRAINAGE 155 



of winter irrigation. The precipitation usually occurs in winter 

 in the form of rain, and large quantities of creek water are then 

 available. This water is spread over the orchards in January, 

 February, and March, when the deciduous trees are dormant. 

 The most favorable conditions for this practice are a mild winter 

 climate, a deep, retentive soil which will hold the greater part 

 of the water applied, deep-rooted trees, and a soil moist from 

 frequent rains. 



In the colder parts of the arid region winter irrigation is like- 

 wise being practiced with satisfactory results. The purpose is not 

 only to store water in the soil but to prevent the winter-killing of 

 trees. Experience has shown that it is not best to apply much 

 water to orchards during the latter part of the growing season, 

 for this tends to produce immature growth, which is easily dam- 

 aged by frost. In many of the orchards of Montana, no water is 

 applied in summer irrigation after August 20. However, owing 

 to the prevalence of warm Chinook winds, which not only melt the 

 snow in a night but rob the exposed soil of much of its moisture, 

 one or two irrigations are frequently necessary in midwinter. 



Drainage in irrigated orchards. The loss of water is not the 

 only effect of deep percolation. The water which escapes in this 

 and other ways usually moves through the soil rather slowly until 

 it reaches some underground body of water at a lower level. If 

 orchards have been planted at these lower levels when the subsoil 

 was dry, the rise of the ground-water level should be carefully 

 watched. The small post-hole auger is one of the most convenient 

 tools to use in making test wells to keep track of the behavior of 

 the ground water. Before the deepest roots of the fruit trees are 

 submerged, artificial drainage ought to be provided, otherwise 

 the ground water will at first lessen the yield and finally destroy 

 the trees. 



The drainage of orchard tracts is usually accomplished in more 

 or less distinct and separate stages. When the ground water 

 begins to be a menace the natural ravines in the vicinity are 

 cleared of weeds and other rubbish and deepened. If the ground 

 water continues to rise, the open drains are deepened and extended 

 or else the excess water is withdrawn through covered drains. 

 Open drains in orchards occupy valuable land, obstruct field work, 



