10 



BULLETIN 546, U. S. DEPARTMENT OF AGRICULTURE. 



Except for a very slightly lower average moisture content in the 

 first foot of the fall-irrigated plats sampled May 24, the moisture 

 determinations made in 1915 disclosed no differences large enough to 

 be considered significant between the fall-irrigated plats and the 

 checks. As in the spring of 1914, the soil on all the plats sampled con- 

 tained an abundant supply of moisture. As the moisture content of 

 all the plats before the first irrigation was found to be substantially 

 the same, no further moisture determinations were made during the 

 season. 



Soil moisture in 1916. — The first irrigation in 1916 was applied 

 July 6. Soil-moisture determinations were made to a depth of 2 feet 

 on all the plats in oats, wheat, and barley on June 10, and the plats in 

 potatoes, beets, corn, and flax were sampled to the same depth on 

 June 30. The results of the two samplings are summarized in Table 

 VIII, which also shows the probable errors of the averages of mois- 

 ture content. 



Table VIII. — Summary of the results of soil-moisture determinations made in 1916 in 

 the fall-irrigation experiments at the Belle Fourche Experiment Farm. 





Depth. 



Fall-irrigated plats. 



Check plats. 





Date. 



Num- 

 ber of 

 plats 

 aver- 

 aged. 



Moisture 

 content. 



Num- 

 ber of 

 plats 

 aver- 

 aged. 



Moisture 

 content. 



Difference 



in favor 



of fall 



irrigation. 





Feet. 

 1 

 2 

 1 

 2 



6 



6 



8 

 8 



Per cent. 

 27.7±0.6 

 29. 2± .8 

 29. 7± .6 

 30. 2± .3 



6 

 6 



8 

 8 



Per cent. 

 27.4±1.0 

 29. 2± .9 

 29.9±1.2 

 30. 1± .4 



Per cent. 

 +0.3±1.2 



Do 



±1.2 



June 30 



- .2±1.3 



Do : 



+ .1± .5 







The results of the soil-moisture determinations made in 1916 were 

 practically the same as those secured in 1915. The soil on all the 

 plats contained an abundance of moisture at the time of sampling, 

 and there was no significant difference between the moisture content 

 of the fall-irrigated plats and that of the checks. 



The results of the determinations made during the three years may 

 be summarized by the statement that any higher soil-moisture con- 

 tent resulting from fall irrigation was found only at times when the 

 soil on both the fall-irrigated plats and the check plats was well sup- 

 plied with water and that all significant differences in soil moisture 

 disappeared early in the growing season, so that the crops showed no 

 effects of fall irrigation. 



CHARACTER OF SOIL THE DETERMINING FACTOR. 



The fact that fall irrigation produced no effect on crop yields at 

 Belle Fourche while it resulted in decidedly higher yields at Scotts- 

 bluff makes it desirable to compare the rainfall and the soil con- 

 ditions at the two places. The comparison is shown in Table IX. 



