Rice Production in Southwestern Louisiana 19 
1,213 pounds greater than the average yield obtained by the use of 
acid phosphate alone. It also is 711 pounds greater than the average 
yield from the* combination of sulphate of ammonia and sulphate of 
potash, which gave the highest yield of any commercial fertilizer 
that was applied. At the beginning of these experiments this soil 
was well supplied with organic matter and in a good physical condi- 
tion, owing to the previous growing of soybeans. The production 
of the season of 1919 was not maintained, because the soybean crop- 
ping was discontinued. At the end of five years the unfertilized 
plats produced an average acre yield of 915 pounds less than the 
plats where the soybean rotation was continued. From these ex- 
periments it is safe to conclude that the Crowley silt loam is not 
as yet deficient in mineral plant foods and that yields may be main- 
tained and increased if this soil is adequately drained and supplied 
with organic matter. 
A virgin soil is fertile because of the availability of the plant-food 
elements. In the cultivation of the soil the plant food is removed 
year by year through leaching and by the growing crops. It must be 
replaced or the mineral elements within the soil must be made avail- 
able if profitable production is to be maintained. 
Plant food is made available by chemical and biological processes 
which take place naturally in an aerated soil supplied with humus. 
The products of these processes include various organic and inor- 
ganic acids which are effective as solvents for the mineral plant food. 
The production of these solvents is greater in soils with a supply of 
humus than in soils deficient in decayed organic matter. 
Humus, which is so essential for soil fertility, is the product of de- 
composed organic matter that has lost the physical structure of the 
materials from which it was made and has been thoroughly incorpo- 
rated in the soil mass. Its supply can be increased in the prairie soils 
of southwestern Louisiana by growing the Biloxi soybean, to be 
plowed under after harvest. Any legume that will grow well under 
rice-field conditions may be used for the same purpose. 
During the early period of the rice industry in southwestern Louisi- 
ana the natural drainage of these level prairies was not sufficient to 
permit the proper preparation of the land for seeding or for harvest- 
ing the crop. This was shown in poor average stands and in losses 
that always occurred at harvest, because irrigation water could not 
be removed promptly enough for the use of machinery before the 
grain began to shatter. About 15 years ago, however, the importance 
of efficient drainage was recognized, and drainage districts were or- 
ganized. These projects resulted in an important general improve- 
ment in the rice-producing areas. Subsequent experience has shown 
that the soils of these prairies when well drained respond to good 
tillage and produce good crops of rice without the use of commercial 
fertilizers. The average yield of 33.7 bushels of rice per acre for 
southwestern Louisiana during the 13-year period from 1911 to 1923, 
inclusive, has been maintained largely by the better soil conditions 
produced by good drainage. 
IRRIGATION EXPERIMENTS 
Fresh water in large quantities is needed to meet the requirements 
of the rice crop. In southwestern Louisiana the supply must be large 
