18 
BULLETIN 1155, U. S. DEPARTMENT OF AGRICULTURE. 
highest yield was obtained by submerging the land 2 inches deep 
during the period of submergence. 
The highest average yield, 3,925 pounds per acre, was obtained 
by submerging the land 6 inches deep throughout the submergence 
period. The average yields in the depth-of -submergence experi- 
ments are shown graphically in Figure 8. 
^ 6\ 
Al/EftAG£ WELD P£ft A?/?£ (P0l/Af0s) 
\ 3,7 6 9 
M 3,339 
■■ 3925 
3,634- 
Fig. 8.— Average acre yields of Wataribune rice obtained in the depth-of-submergence experiments at 
the Biggs Rice Field Station during the 8-year period from 1914 to 1921, inclusive. 
The average increase in yield of the 6-inch submergence over the 
4-inch submergence was 86 pounds per acre; over the 8-inch sub- 
mergence, 91 pounds per acre; and over the 2-inch submergence, 156 
pounds per acre. These are small average increases. However, in 
1914 and 1915 on new and second-year land there was a distinct 
advantage from holding deep rather than shallow water. On old 
land, if water-grass control is not involved, shallow submergence 
appears to be just about as good as deep submergence. The average 
yields for the 8-year period show that the 6-inch depth ranks first, 
the 4-inch depth second, the 8-inch depth third, and the 2-inch depth 
fourth. 
Table 13. — Annual and average yields obtained in the irrigation depth-of-submergence 
experiments with Wataribune rice at the Biggs Rice Field Station, Biggs, Calif., from, 
1914 to 1921, inclusive. 
Depth of submergence. 
Yield per acre (pounds). 
L 
1914 
1915 
1916 
1917 
1918 
1919 
1920 
1921 
Average. 
5,010 
5,490 
5,670 
5,220 
4,030 
4,290 
4,510 
4,400 
3,620 
3,760 
4,260 
4.440 
4,635 
4. 215 
3,000 
2.990 
2,655 
2,655 
2,435 
2,690 
2,940 
2,875 
3,280 
3,220 
3,769 
3,839 
3,925 
3,834 
3,900 4.520 4.035 3.050 
8 inches 
3,940 
4,480 
4,t)15 
2,710 
i Yields from single fifth-acre plats in 1914, 1915, 1916, 1918, and 1920, and from duplicated tenth-acre 
plats, in 1917, 1919, and 1921. 
The data available indicate that on new land the water should be 
held at least 6 inches deep, while on old land it should be held from 
4 to 6 inches deep. 
STAGNANT AND SLOWLY CHANGING WATER. 
Table 14 shows the yields obtained from the different water treat- 
ments during the 8-year period from 1914 to 1921, inclusive. The 
average yields are shown graphically in Figure 9. During the sub- 
mergence period, under ordinary conditions water is entering the 
checks continuously. The quantity of water used, if carefully 
handled, is just enough to keep the checks submerged to a constant 
depth. In other words, enough water is entering the field each day 
to replace that lost by evaporation, transpiration, and seepage. 
