22 
BULLETIN 1387, U. S. DEPARTMENT OF AGRICULTURE 
The soil on which these yields were obtained is Stockton clay- 
adobe. From 1913 to 1920, inclusive, the land was fall plowed 
(except in 1918), well prepared in the spring, and kept free from 
water grass and cat-tail. For the 1918, 1922, and 1923 crops the 
land was spring plowed, and for the 1924 crop the land was winter 
plowed. In each of these years a reasonably good seed bed was pre- 
pared after plowing. From 1913 to 1920, inclusive, the rice was 
grown by the old method of irrigation, all rice was sown with a drill, 
and water grass and cat-tail were hand pulled. In 1922, 1923, and 
1924 the five plats averaged for the yearly yield were treated as fol- 
lows: One plat was drilled on April 25 and irrigated in the old way* 
a second plat was sown broadcast on April 25 and immediately sub- 
merged 8 inches; a third plat was sown broadcast on May 15 and 
immediately submerged 4 inches; a fourth plat was sown broadcast 
in 6 inches of 
water on May 16; 
and a fifth plat was 
sown broadcast 
and immediately 
submerged on 
May 25. The av- 
erage acre yields 
of these five plats 
are lower than 
they should be 
each year, because 
both good and 
poor methods of 
production are in- 
volved, and only 
the best method 
should be consid- 
ered in such an 
experiment. 
Land on which 
Fig. 5.— Annual yields of rice grown continuously at the Biggs Rice Field riCe ^ aS n °^ Deen 
Station on the same land from 1913 to 1924, with one intervening vear of PTOWIl before USU- 
fallow in 1921 & , i j 
ally produces 
about 30 per cent more per acre than second-year or third-year land. 
The annual yields presented in Table 13 do not show a gradual 
decline with continued cropping, but they show erratic changes prob- 
ably due to favorable or unfavorable weather conditions in different 
years. The yield in 1914 on second-year land was less than that for 
1915 on third-year land. Likewise, the yield for 1916 on fourth-year 
land was less than that for 1917 on fifth-year land, and the yield in 
1917 was just about the same as that for 1914. Such fluctuations in 
yield from year to year are to be expected, and they emphasize the 
important effect of seasonal conditions as well as soil upon crop yields. 
^ SOOO 
\ 
I 
. tooo 
I 
\ 
3 zooo 
\ 
\ 
\ 
* 
\ 
1 
\ 
\ 
GO/VT^/SVC/CHS^ C>eO/2f>//VG TO JZ/C£r 
