186 EXPERIMENT STATION EECOED. 



tions the valley silt loumwas found to have a maximum capillary water content 

 of about 34 per cent, a maximum content for proper cultivation of about 27 

 per cent, an optimum water content of about 23 per cent, a drought point 

 content of about 14 per cent, and a minimum moisture content of about 11 

 per cent. 



Irrigation caused a higher seasonal moisture content but was associated with 

 temporary loss in moisture in the subsoil, which was, however, regained between 

 irrigations. The highest seasonal moisture content in irrigated plats was 

 obtained in connection with early spring plowing, manuring, crop rotations, 

 including legumes, and frequent cultivation. Irrigation caused a lowering of 

 the temperature of the surface soil as much as 4° in cultiv.ited plats and 10° 

 in meadows, but caused an increase in yield of all crops, which averaged about 

 65 per cent for a 7-year period. 



Kale, clover, and beets did better with one irrigation than with two and the 

 reverse was true for potatoes. The use of 4 acre-inches of water per acre in 

 the wet season and of about 6 acre-inches in the dry season pi'oduced the most 

 economical increase of alfalfa, while the maximum yield was obtained with 

 6 in. in a wet season and 12 in. in a dry season. The most economical return 

 with potatoes was obtained with 2 in. in a wet season and with 3 or 4 in. in a 

 di-y season, while the maximum yield with potatoes was secured with 3 in. in 

 a wet season and 6 in. in a dry season. Clover was best irrigated on gray 

 silt loam when the moisture content of the first 2 ft. dropped to about 14 per 

 cent, while potatoes were best irrigated on this soil when the moisture content 

 of the first foot dropped to 20 per cent. Potatoes did best with a uniform 

 moisture content. Water was best distributed over this soil by the corrugation 

 method. 



" Irrigation has made it xiossible to raise two difi'erent crops in one season, 

 and not only to get a cutting from new seeding of clover or alfalfa the first 

 season, but also to secure a more perfect stand. It was found that under field 

 conditions the use of a moderate amount of irrigation greatly reduced the 

 water cost of dry matter, which varied about as the most economical returns 

 per acre-inch, above which the water cost increases. The time and frequency 

 of irrigation also afifected the water cost. Growing crops in an irrigated rota- 

 tion, including a legume, greatly decreased the water cost of dry matter as 

 compared to growing crops in an uuirrigated rotation following an unirrigated 

 legume crop. The water cost under field conditions varied with the different 

 crops and crop varieties. Kale and potatoes proved to be crops of high water 

 requirement, while the reverse was true with corn and beans. 



At a maximum price of $1 per acre-inch, irrigation ^ith pumped water ap- 

 plied to ordinary field crops made an average profit of $2.66 per acre-inch. 

 Electricity proved more economical than gasoline as a source of eueregy for 

 a small pumping plant where labor cost was more important than fuel cost. 



Proper irrigation did not injure the palatability of potatoes, decreased the 

 percentage of culls, and did not increase the moisture content of crops except 

 where irrigation was excessive.. However, it altered the shape and size of 

 plants, caused better shaped ears and a higher percentage germination in corn, 

 a lower percentage germination in beans, and altered the percentage of market- 

 able product, causing more beans in proportion to plant, more beets in propor- 

 tion to top, but more vines in proportion to potatoes. 



Irrigation caused a slight decrease in soil water capacity, an increase in 

 volume weight where rank field crops were grown, but caused an impro\enient 

 in this respect where soil-building crops were grown. It had little appreciable 

 effect on the acidity or the available plant food content, and caused a decided 

 increase in organic content where leguminous crops wex'e grown. 



