18 Bulletin 1356, U. S. Department of Agriculture 
Sulphate of ammonia, nitrate of soda, and cottonseed meal also 
were used in these experiments as sources of nitrogen, but when 
applied alone they did not increase yields. Sulphate of ammonia 
applied at the rate of 100 pounds per acre with 100 pounds of sul- 
phate of potash, however, caused an increase in yield slightly above 
that produced by sulphate of potash alone. 
Sulphate of potash applied at the rate of 100 pounds per acre 
produced an increase in yield when used alone and with sulphate of 
ammonia. These yields might be interpreted to mean that the 
Crowley silt loam is deficient in potassium, yet the increased yields 
obtained after a crop of soybeans indicate that this element prob- 
ably is present in sufficient quantities to meet the requirements of 
rice and becomes available when vegetable matter is added to the soil. 
An application of 2,000 pounds of horse manure gave a greater 
average yield of rice than was obtained from plats that did not 
receive any kind of fertilizer. Manure is an excellent source of plant 
food, and its effect on the physical condition of the soil and the 
availability of soil plant food is beneficial. The quantity of horse 
manure on a rice farm, however, is too small to be of practical service 
to the producer of rice. 
In the experiment to determine the effect of lime on the yield of 
rice, limestone was applied only in 1919. 1920. and 1923. The low 
yields obtained after this treatment in 1920 probably were due to an 
excess of lime, and on that interpretation no limestone was applied in 
1921 and 1922. The better yields of 1921 probably were due to the 
removal of any excess of lime added to the soil in 1919 and 1920 and 
to the stimulating effect from the smaller quantity still remaining in 
the soil. In 1923 limestone did not increase the yield of rice. Lime- 
stone at the rate of 6.000 pounds per acre retards the growth of the 
young rice plants. The same effect is produced when limestone is 
applied each year at the rate of 2,000 and 1.000 pounds per acre. 
Sedges which often become troublesome weeds are greatly reduced in 
number when lime is applied. The results indicate that the yield of 
rice may be increased by the application of limited quantities of 
limestone at intervals of several years. 
The average yield of rice obtained from the use of a complete 
commercial fertilizer was 205 pounds less than the average yield ob- 
tained without the use of any fertilizer. A complete commercial 
fertilizer with limestone at 1.000 pounds per acre produced a larger 
average yield than with no limestone but still 24 pounds less than the 
average yield when no fertilizer was used. 
The best yields of rice in these experiments were obtained not by 
the use of fertilizers but by growing the crop in rotation with soy- 
beans. The data show that yields produced from the use of manure 
and limestone and from the use of commercial fertilizers applied 
alone and in combination were each year much smaller than the 
yield- when the crop was grown in the soybean rotation. TTith the 
exception of dried blood and sulphate of potash alone and in com- 
bination with sulphate of ammonia, the use of commercial fertilizers 
did not increase rice yields on Crowley silt loam which had been 
effectively drained and well prepared for seeding. whereas the turn- 
ing under of the mature soybean plants greatly increased rice yields. 
An average yield of 2,353 pounds of rice' per acre was secured 
when the crop was grown in rotation with sovbeans. This vield is 
