IRRIGATION OF FIELD CROPS. 109 



sary to use water sooner than on unmanured soil. One 

 good watering will often mature a crop of potatoes, but 

 if the growth of vines is heavy and shades the ground 

 well, two, or even three, waterings will increase the 

 yield and can in no ordinary case injure it. Each appli- 

 cation of water should be followed immediately with 

 thorough cultivation, until the vines are too large or 

 the tubers too near grown to permit of it. Nothing is 

 so damaging to a growing crop as to leave the furrow or 

 gutter in which the water has run to bake and dry in 

 the sun. Even when the advanced growth of the vines 

 and tubers will not permit it near the base of the hill, 

 cultivation may still continue with profit as long as the 

 furrow is in sight in the middle of the row. 



In watering, it is best not to try to run water 

 through too long rows. As a rule it is best not to have 

 the rows over 40 rods in length. If the ground is very- 

 steep, of course the water will run quickly through, but 

 it will have to run longer than in a row with less fall, 

 to give it time to soak in ; and if the rows are too long, 

 by the time the water is through and the lower 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 



