RICE CULTURE IN CALIFORNIA 
11 
Table 7 shows the average agronomic data for Caloro rice grown 
by the old method of irrigation (check) and by continuous submer- 
gence for different dates of seeding during the three years 1922, 1923, 
and 1924. All plats were submerged about 6 inches. The check plats 
were drilled on April 25 and the average date of the first irrigation 
was April 27. They were then drained and again irrigated and drained 
at intervals until 30 days after the rice had emerged, when the 
plats were permanently submerged until drained for harvest. The 
other plats were sown broadcast and immediately submerged. After 
submergence the water was held continuously at as nearly a uniform 
depth as possible under field conditions until the land was drained 
for harvest. The average time required from the date of the first 
irrigation to emergence of drilled rice was 17 days and for broadcast 
rice about 21 days. The number of days between the date of first 
irrigation or submergence and maturity varies with the date of seed- 
ing and method of irrigation. Drilled rice irrigated by the old method 
is slower in reaching maturity than rice sown broadcast and immedi- 
ately submerged. The time gained by continuous submergence over 
the old method of irrigation is 5 days for the early-sown rice. The 
comparison for the later dates is not a true measure of the actual dif- 
ference, since all dates of broadcast seeding are compared with the 
early-sown check plats. A check plat sown on each date of seeding 
would give a more accurate comparison. However, the results show 
that rice sown broadcast and immediately submerged requires from 5 
to 10 days less time to reach maturity than rice irrigated in the old way. 
This gain in maturity of from 5 to 10 days by continuous submer- 
gence is a very important point in favor of this method of irrigation 
and in certain years may mean the difference between success and 
failure. It also indicates the possibility of growing later-maturing 
varieties in normal years without unduly delaying harvest, and this 
would probably mean larger acre yields. 
Table 7. — Average agronomic data for Caloro rice grown by the old method of 
irrigation and by continuous submergence immediately after broadcast seeding at 
the Biggs Rice Field Station in 1922, 1923, and 1924-' 
Variety 
Date of- 
Seeding 
Sub- 
merg- 
ence 
Emer- 
gence 
Caloro (check) . Apr. 2." i 
Caloro 
Do 
Do 
Do. 
..do 
May 5 
M xv 15 
May 25 
June 15 
Apr. 26 
May 5 
May 15 
May 25 
May 14 
Juce 4 
June 15 Aug 
heading 
Full 
heading 
First 
ripe 
Ripen- 
ing 
, Days 
from 
, first 
irriga- 
tion 
to ma- 
turity 
Days 
gained 
in 
com- 
parison 
with 
check 
Aug 22 Sept. 1 
Aug. 15 Aug. 26 
Aug. 19 Aug. 29 
Aug. 24 
27 
Sept. 3 
Sept. 6 
Sept. 13 
■ 
Sept. 11 
Sept. 19 
Oct. 3 
Sept. 27 
Sept. 30 
Oct. 9 
154 
142 
137 
The average date of first irrigation was April 27 
COMPARISON OF AIR AND WATER TEMPERATURES 
Rice is commonly sown in California between April 15 and May 15. 
At this time the temperatures of the air. water, and soil usually are 
too low for maximum germination. During the growing season of 
1923 and 1924 a soil thermograph was used to get temperature rec- 
ords on a plat sown broadcast and submerged 6 inches on April 25. 
