236 IRRIGATION FARMING. 



end is wet enough, the upper end will have had too 

 much. If the ground has too little fall, the least clod 

 will clog up the rows and flood the surface. See that 

 there is a free opening at the lower end of each row, or 

 the water will back up in row after row for rods, and 

 flood and ruin the crop. In sandy soils water should 

 not continue to run more than three or four hours, 

 while in tenacious soils the irrigation may continue 

 eight or ten hours at a time. 



After once irrigating it is very important that the 

 ground should never be allowed to become dry, thus 

 stopping the growth of the potato. For if we permit 

 the growth of a potato to stop, and by irrigation it 

 again starts to grow, it will either increase irregularly 

 in size or set a second crop, thus giving a large number 

 of small potatoes or a crop of ill-shaped ones. The 

 irrigation is usually discontinued about the first of 

 September, although if it is a dry fall a later irrigation 

 may be needed. A potato field under irrigation is the 

 subjecft of Fig. 61. 



Around Greeley, Colorado, where potatoes are so 

 successfully raised, though they may appear to need 

 water, the farmers are careful not to irrigate them until 

 after the young tubers are set. The reason for this is 

 obvious. When irrigated immediately before setting, 

 a greater number of potatoes will be formed than the 

 plant can properly support, few of them becoming large 

 enough for market. When the tubers are allowed to 

 form first and are irrigated afterwards, fewer potatoes 

 will form in each hill, but a large crop of marketable 

 tubers is the result. Keeping the ground mellow by 

 thorough and deep cultivation is important. If the 



