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. Kecently, 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 



