20 
BULLETIN 1155, U. S. DEPARTMENT OF AGRICULTURE. 
per acre, in 1920, to 2,860 pounds per acre, in 1918. The average 
yield for the 8-year period was 1,925 pounds per acre (Table 14). 
Rice grown in this way stools less than that grown on submerged 
land, does not grow as tall, has shorter and fewer heads per plant, is 
not as vigorous, and produces grain of inferior quality. This method 
of irrigating rice should not be attempted commercially in California, 
because plenty of water for irrigation and submergence is essential 
for successful rice production. 
FERTILIZER EXPERIMENTS. 
For many years previous to the introduction of rice growing, the 
Stockton clay adobe soil in the Gridley and Biggs area was used for 
dry-land grain farming, pasture, and hay production. The 18 to 36 
inches of black surface soil rest upon a gray calcareous hardpan 
which is practically impervious to water. No leguminous crops do 
well on this soil, and for that reason the limiting element in crop 
production is likely to be nitrogen. 
Loughridge 6 shows the humus and humus nitrogen of California 
soils to be as stated in Table 15. 
Table 15. — Humus and humus nitrogen in the soil of the Sacramento Valley. 
Soil content (per cent). 
Humus. 
Humus nitrogen. 
Nature of soil. 
First 
foot. 
Upper 
3 feet. 
12 feet. 
First 
foot. 
Upper 
3 feet. 
Average 
per foot . 
Sum. 
Average 
per foot. 
Sum. 
Alluvial soils 
1.47 
1.16 
.95 
.47 
0.92 
.73 
.77 
.30 
2.76 
2.20 
2.39 
.90 
0.67 
.31 
7.50 
3.62 
0.08 
.06 
.05 
.03 
0.06 
Black clay adobe 
.04 
Gray clay loams 
.42 ! 5.02 
.15 1-43 
.05 
Red mesa lands 
.02 
Doctor Loughridge comments on the humus content of Sacra- 
mento Valley soils as follows : 
It would naturally be supposed that because of their deep color the black clay 
adobe soils would contain more humus than any other soil, but the above results 
show that such is not the case, for the alluvial soils are richer, and even the gray 
loams have nearly as much as the black adobe m the first foot and are a little richer in 
the rest of the column. The color of a soil, then, is no certain guide as to the relative 
amount of humus it contains. Humification is retarded in close compact adobe clays, 
and the amount of humus is less than in lighter loam and sandy soils. 
Fertilizer experiments were started at Biggs in the spring of 1914. 
The original plan followed during 1914, 1915, and 1916 was to apply 
the fertilizer to the land before seeding. In 1917 the plan was 
changed, and the fertilizers were applied at three dates during the 
growth of the rice crop, namely, (a) when the rice was 3 inches in 
height, (b) when the heads were emerging, and (c) two weeks after 
the first heads appeared. This plan was followed during 1917, 1918, 
and 1919. 
6 Loughridge, R. H. Humus in California soils. Calif. Agr. Exp. Sta. Bui. 242, p. 62. 1914. 
