20 
BULLETIN 138*L U. S. DEPARTMENT OF AGRICULTURE 
each variety probably will produce its maximum average yield at 
some constant rate of seeding. It is not possible to conduct a rate- 
of-seeding experiment for each variety, because of the large number 
of varieties. Recommendations as to the best rate of seeding are 
therefore usually based on the results of rate-of-seeding experiments 
with one or two of the leading commercial varieties grown in a 
given area. 
The rate of seeding rice is influenced by many factors, some of the 
most important of which are variety, age of seed, quality of seed, 
date of seeding (temperature), depth of seeding, method of seeding, 
condition of the seed bed, method of irrigation, and kind of land, 
whether new or old, rich or poor. 
In 1921 a rate-of-seeding experiment was started, including three 
varieties of rice — Selection No. 175, Caloro, and Wataribune (C. I. 
No. 1561). The land 
^^° used for this experi- 
ment was fallowed in 
1920. The 1921 crop 
was therefore grown 
on fallow land, and 
the 1922 and 1923 
crops were grown on 
spring-plowed stub- 
ble land. 
Each varietal rate- 
of-seeding experiment 
was located on the 
same plat each year. 
A reasonably good 
seed bed was pre- 
pared before seeding. 
The rates of seeding 
for each variety 
ranged from 85 to 175 
pounds per acre. The 
rice on all plats was 
Tls sown with a drill on 
the same date each 
Fig. 4. — Average yields of three rice varieties grown in rate-of-seed- year. 
iug experiments at the Biggs Rice Field Station in 1921, 1922, and After Secdin " all 
plats were irrigated 
and drained at frequent intervals until 30 days after the rice emerged. 
The land then was submerged about 6 inches and the water held 
at this depth until the land was drained for harvest. Each year 
the water grass which appeared was hand pulled before it reached 
maturity. 
YIELD DATA 
Table 12 presents the annual and average acre yields for the rate- 
of-seeding experiment with Selection No. 175, Caloro, and Watari- 
bune in 1921, 1922, and 1923. The average data are shown graphi- 
cally in Figure 4. For Selection No. 175 the average acre yield 
increased for each increased rate of seeding from 85 to 150 pounds 
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