14 



BULLETIN 157, U. S. DEPARTMENT OF AGRICL'LTTJRE. 



practically the same on all plats during the fallow season: and (4) 

 that the average percentage of moisture in the fall was lower for the 

 plats subsoiled to a depth of 18 inches than for any of the other plats. 

 These facts are shown graphically in figures 5, 6, and 7. 



The points thus brought out show that, so far as soil moisture is 

 concerned, there was no advantage in deep plowing or subsoiling, for 

 the moisture content of the plat plowed 5 inches deep (shallow plow- 

 ing) was as high as that of any of the others. So far as the prepara- 

 tion of a seed bed is concerned, however, it was found that in most 

 cases the shallow plowing was less desirable because the stubble was 

 not turned under as well as by the deeper plowing. Because of this 

 the surface of the shallow-plowed plat usually contained much trash, 



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DEPTH /A/ PE-ET 



Fig. 6. — Graphs comparing the average percentage of moisture in each of the upper 6 feet of soil at the 

 beginning, in the middle, and at the end of the fallow season, as found in the fall depth-of-plowing 

 tests at the Nephi substation, 1909 to 1912, inclusive. 



which interfered somewhat with the operation of the drill when the 

 plat was seeded. 



YIELD OF GRAIN. 



The annual and average yields of the plats in these tests are pre- 

 sented in Table V and are shown graphically in figure 8. 



Table V. — Annual and average yields of winter wheat on plats v^ed in the depth-of- 

 plovnng tests at the Nephi substation, 1910 to 1913, inclusive. 



Treatment. 



Yield per acre of grain (bushels). 



1910 



Average. 



Subsoiled 18 inches deep 

 Subsoiled 15 inches deep 

 Plowed 10 inches deep. .. 

 Plowed 5 inches deep. . . 



16.0 

 16.7 

 17.5 

 17.2 



