92 



the appearance of the plants such as the darkening of the leaves, or prefer- 

 ably by an examination of the soil under the surface where the tubers form. 

 The soil is in good condition when a ball of earth squeezed in the hand 

 will retain its shape. 



The last irrigation should be applied before the growth of tuber ceases 

 in order to give about one month and a half to two months for ripening in 

 dry earth. Where potatoes are grown between tree rows, late irrigation 

 and cultivation after the first of August will keep the orchard in growing 

 condition too late in the fall and will not give tte wood sufficient time to 

 mature before the first hard frosts. 



7. Method of Irriagtion. 



Potatoes are irrigated by furrows made midway between the rows. The 

 furrows are made by a double mouldboard plow which forms a V trench, 

 the bottom of which should be about 6 to 12 inches below the crown of the 

 plant. The length of the furrows should not be over 200 or 300 feet for 

 porous sandy soil and not over 500 to 6CO feet for more retentive loam. 

 Greater lengths give unequal distribution of soil moisture with an excess 

 or waste at the upper end due to deep percolation. 



A common practice in Colorado is to open alternate furrows for the first 

 irrigation, and for the next irrigation open the furrows in the intervals 

 between rows which were left unopened in the first irrigation. For more 

 than two irrigation the alternation is repeated. 



The division of water between furrows, the size of the stream delivered 

 to each furrow, t^e length of time the stream is run into the furrows, are 

 the saire and controlled by the same factors as the irrigation of orchard 

 and alfalfa by furrows previously described. 



Potato vines are shallow rooted and the frequent application of cold 

 water no doubt retards their growth; for this reason some irrigators prefer 

 to apply the water at night when the soil and water have had all day to 

 warm up in the sun. This practice also has the advantage that the loss of 

 moisture by evaporation is decreased. Many growers object to night irri- 

 gation because of the night work necessary to distribute the water. How- 

 ever, this may be cut down to a minimum by a proper preparation of the 

 ground and the regulation of the water delivered to the furrows by placing 

 spouts in the banks of the head ditch at the head of each furrow or by 

 using for tte head ditch a flume with auger holes as described for orchard 

 irrigMion. 



Additional information on the agricultural phase of potato growing 

 may be otbained by consulting the following bulletins: 



Potato Investigations, Bulletin No. 94, Agricultural Experiment Sta- 

 tion, Pullman, Washington. 



Potato Culture on Irrigated Farms of the West, Farmers' Bulletin 386, 

 U. S. Department of Agriculture, Washington, D. C. 



VII. IRRIGATION OF ALFALFA. 



The value of alfalfa as a forage crop and as a foundation crop for 

 orchards or potatoes to be grown on soils lacking fertility, make it desir- 

 able that information on the proper methods of irrigation of this crop be 

 included in this bulletin. The growing of alfalfa is not widespread in 

 British Columbia, but its rapid spread in almost every state of the United 

 States makes it reasonable to expect that it will become a more import- 

 ant crop 



