RICE EXPERIMENTS IN CALIFORNIA. 51 
that depth until the rice had emerged through the water; then the 
depth was increased to 6 inches and held continuously until the 
rice was ready to drain for harvest. 
Plat 5 was sown broadcast at the rate of 150 pounds per acre on 
May 16 on spring-plowed rice stubble with the same seed-bed prep- 
aration as plat 4. After May 21 this plat was kept wet with some 
water standing on low spots until the rice was about 2 inches high. 
The water was then increased to about 6 inches and held contin- 
uously until the rice was ready to drain for harvest. 
On spring-plowed rice stubble with the same seed-bed preparation 
as plat 4 rice was sown broadcast on plat 6 at the rate of 150 pounds 
per acre and the plat submerged 6 inches deep on May 21. The 
water was held continuously at that depth until the rice was ready 
to drain for harvest. 
Plat 7 was spring-plowed rice stubble with the same seed-bed prep- 
aration as plat 4. This plat was submerged on May 21, and the 
rice was sown broadcast in the water at the rate of 150 pounds per 
acre on May 25. The water was held 6 inches deep continuously 
until the rice was ready to drain for harvest. 
In 1913, 1914, and 1915 the land on which the water-grass control 
experiment was conducted in 1921 was part of a commercial rice 
field, and the last year it was very foul. In 1916 the land was fallow 
with cultural methods for water-grass eradication; in 1917 it was 
sown to grain sorghums and cultivated to kill grass. In 1918 this 
land was sown to rice and the water grass pulled; in 1919 it was 
fallow with cultural methods for water-grass eradication; and in 
1920 it was sown to rice and was very foul with water grass. 
The fact that the grass was pulled in 1918 and no grass was allowed 
to mature seed during the fallow year 1919 would lead one to expect 
the land to be reasonably free from grass in 1920, but instead it was 
very foul. There were no winter floods in 1919 to bring in a new 
supply of grass seed. However, during the 4-year period from 1916 
to 1919 the land had been cultivated rather shallow each year to 
eradicate the grass, while in 1920 it was spring-plowed rather deep. 
This deep plowing apparently brought to the surface a new supply 
of grass seed that had been in the ground below the depth worked 
in previous fallow years, and this seed germinated with the rice 
when irrigated in 1920. 
The yields and agronomic data on the water-grass control experi- 
ments at the Biggs Rice Field Station in 1921 are shown in Table 28. 
The land on which the water-grass control experiments were con- 
ducted apparently increases in fertility from plat 1 to plat 7; there- 
fore, the irrigation methods that were most effective in the control 
of the grass did not necessarily result in the highest yields per acre. 
The rice on all plats had partly emerged through the water on 
June 13, and the elongated plants were lying on the surface. Near 
the levees, where the water was 8 to 10 inches deep, considerable rice 
was killed by the formation of a scum on the surface of the water. 
This scum prevents the rice from emerging through the water. A 
scum is usually present when crops are grown by continuous sub- 
mergence and often causes poor stands on low spots where the water 
is 10 to 12 inches deep. On June 25 the elongated rice plants were 
still floating on the surface of the water, but by July 2 most of the 
plants were erect. The stands ranged from fair to excellent. 
