26 BULLETIN 1387, U. S. DEPARTMENT OF AGRICULTURE 
represented by Selection No. 115, ranked second, and the long-grain 
mid-season group, represented by Selection No. 113, ranked third in 
yield. The only divergence from the six-year averages noted in the 
shorter periods is in the replacement of the medium-grain mid-season 
Early Prolific, occupying fourth place during the first three-year 
period, by the short-grain early group, represented by Colusa, during 
the second three-year period. The change in relative rank of these 
two groups during the second three-year period also was great enough 
to give a similar ranking for the five-year period from 1920 to 1924, 
inclusive. 
The average yields of the highest producing mid-season and late 
short-grain rices during the six-year period from 1919 to 1924, inclu- 
sive, are nearly the same. The difference in average yield of the 
highest yielding varieties in these two groups is probably not sig- 
nificant. The highest yielding mid-season and late-maturing short- 
grain varieties, however, undoubtedly are superior to the mid-season 
medium-grain variety Early Prolific, the late long-grain variety 
Honduras, and the early short-grain variety Colusa, while the dif- 
ferences in the average yields of the three varieties last named are 
probably not significant. 
On old rice land the mid-season and late-maturing short-grain 
varieties produce about the same average acre yields, whereas on new 
or rich land the late-maturing varieties are usually most productive. 
This indicates that with continued production the fertility factor is of 
some importance. On the soil at the station rice yields have been 
materially increased by the application of 100 pounds of ammonium 
sulphate per acre or by plowing under a bur-clover crop just before 
sowing the rice. This indicates that this soil (Stockton clay adobe) 
is somewhat deficient in nitrogen, at least to the extent that this 
plant food is a limiting factor in the yields of rice. If nitrogen is 
the limiting factor in rice production on this soil, and if there is only 
sufficient available nitrogen to produce an average acre yield of 3,000 
pounds of paddy rice, then the mid-season short-grain varieties are as 
likely to produce a maximum yield as are the late short-grain varieties. 
That this assumption is correct is shown by the fact that varieties in 
either group are capable under suitable conditions of producing much 
higher average acre yields. 
The leading commercial variety at the present time is Caloro, a 
short-grain mid-season rice. Next in importance is Early Wataribune, 
also of the short-grain mid-season group. The two short-grain early- 
maturing varieties, Colusa (C. I. No. 1600) and Onsen, also are of 
commercial importance. Caloro and Early Wataribune are grown 
both on new and old rice land; Colusa and Onsen are grown only on 
new land or on old land of high fertility. On most of the old rice 
lands the two latter varieties do not yield well because of their 
earliness. 
Table 15 gives the average agronomic data for six varieties of rice 
grown at the station during the seven-year period from 1918 to 1924, 
inclusive. The average date of sowing was April 27, the average 
date of first irrigation was May 2, and the average date of emer- 
gence was May 17, except that for Caloro the date of seeding and 
emergence averaged one day later. 
