SUGAR-CANE CULTURE FOR SIRUP PRODUCTION". 13 
of nitrogen, 3 per cent of phosphoric acid, and 2 per cent of potash. 
Tankage is also extensively used, especially at times when the price 
of cottonseed meal is unusually high. Its composition varies accord- 
ing to the proportions of blood, meat, and bone entering into its 
manufacture, but it averages about 7.5 per cent nitrogen and 5.5 per 
cent phosphoric acid. Dried blood and fish scrap are also occa- 
sionally used, mainly for their nitrogen content. In the tropical 
countries ammonium sulphate containing about 22 per cent nitrogen 
is very extensively used. For quickly available nitrogen, nitrate of 
soda (Chile saltpeter), containing about 15 per cent nitrogen, is the 
favorite. Synthetic nitrogen manures have been introduced recently 
to some extent. 
The source of phosphoric acid in the fertilizer mixtures is nearly 
always acid phosphate, except to the extent that it is furnished by 
the nitrogenous manures, such as tankage or cottonseed meal. The 
acid phosphate contains 14 to 16 per cent of phosphoric acid. For 
soils deficient in lime and with an acid tendency, it is better to supply 
the phosphoric acid in the form of basic phosphate (basic slag or 
Thomas slag): 
The potash was supplied in the past almost exclusively in the form 
of potash salts from the mines near Strassfurt, Germany, either the 
natural mineral, especially kainit with 12 to 14 per cent of potash, or 
the more nearly pure salts, the sulphate of potash and the chlorid 
(muriate) of potash, either one containing about 40 to 48 per cent 
of potash. 
Natural manures, such as green crops plowed under and barnyard 
manure, are highly beneficial in increasing the yield of cane, much 
more so than the plant-food elements contained can account for. 
Practically all soils in the sugar-cane localities, both the heavy soils 
like these in Louisiana and the lighter ones of the States farther east, 
are very responsive to increases in the humus content. The farmer 
should therefore be on the alert to plow under vegetable matter 
whenever it is possible without interfering too seriously with culti- 
vation. The tops and leaves from the cane at harvesting were in 
the past usually burned off to make the field cleaner for the cultiva- 
tion of the stubble crop of cane during the next season and in the 
hope of thereby destroying insect pests. Recently, however, since 
the entomologists of this department have collected evidence which 
tends to show that the damage from insect pests is not reduced by 
burning the trash, many planters have adopted the plan of incorpo- 
rating it with the soil without burning it. Whether or not this prac- 
tice, and whether returning to the field the bagasse, suitably rotted 
or chopped fine, tends to increase the damage from diseases, re- 
mains yet to be determined, and experiments along this line are being 
