The above results show that 16 to- 20 inches of water will give a yield 

 nearly as great and in some cases greater than a larger quantity. This is 

 also corroborated by measurements made by D. H. Bark in Idaho in 1910. 

 The results obtained are given below. 



These potatoes were planted June 1st and 2nd at the rate of 1,000 Ibs. 

 to the acre on fall plowed land which had been in grain during the season 

 of 1909. The land received one irrigation before planting. The water was 

 applied in deep furrows 220 feet long and the land was cultivated six times. 

 Mr. Bark states that the yields were very unsatisfactory owing to the poor 

 stand secured, but it is thought that the amounts applied would have been 

 sufficient for maximum crops had the stand been good. 



While these experiments are not conclusive, they are of value in showing 

 that the bigger yields are not always obtained with the largest quantity of 

 water and that above a certain depth of water the increase in yield, if any, 

 is small as compared to the increase in quantity of water applied. The 

 yield does not depend entirely on the quantity of water applied but on the 

 time of application and the care in planting and cultivation. 



6. Time to Irrigate. 



Soil which is moist and retentive does not need any irrigation before 

 planting, but for dry soil or for late planting one irrigation before planting 

 followed by cultivation, is necessary. During the first stages of growth 

 thorough cultivation is more important than irrigation and no irrigation 

 may be necessary until July. The number of irrigations will vary from 

 two to four for ordinary sandy loam, but on porous, sandy soil or on shal- 

 low soil which does not retain moisture, five or even six shallow irriga- 

 tins may be preferable. Frequent irrigation, especially early in the season 

 when the water is cold, will retard the growth. The moisture in the soil 

 should be kept fairly uniform until the tubers begin to form, when a large 

 quantity of water is required. The need of irrigation may be indicated by 



