COTTON FEETILIZEBS 333 



profitable use of potash. At the several experiment stations and 

 substations in Mississippi and Louisiana its use was unprofit- 

 able ; the South Carolina and Georgia stations recommend it 

 only in relatively small amounts ; and the Alabama Station has 

 found it often profitable, but more useful as a preventive of rust 

 on certain soils than as an ordinary plant-food. 



307. Potash as a means of checking cotton-rust. — On 

 soils very liable to severe injury by attacks of cotton-rust 

 the use of potash is recommended ; for on such soils 

 potash, ordinarily in the form of kainit, has conspicuously 

 decreased the amount of rust and greatly increased the 

 jields. Rust occurs most frequenth' on poor sandy soils, 

 such as are especially common in the class known as the 

 Norfolk soils, which constitute a large proportion of the 

 area of the southeastern part of the cotton-belt. Hence, 

 on such poor sandy soils, potash is more frequently than 

 elsewhere needed for cotton. 



In several hundred local tests conducted bj' the Alabama 

 Experiment Station, 100 pounds of kainit per acre has 

 been highly effective in restraining cotton-rust, apparently 

 about as effective as 200 pounds. 



In one test 60 pounds of kainit effected a noticeable 

 decrease in the injury from this disease. Apparently it 

 is safer to use at least 80 pounds per acre where the pur- 

 pose is to combat rust. 



In the fertilizer experiments in Alabama two facts relative 

 to kainit and cotton-rust are noticeable, viz. (1) the usual favor- 

 able effect of kainit in checking rust, and (2) Its occasional failure 

 on some soils and in some seasons to reduce the injury resulting 

 from this disease. Just how potash decreases rust is not well 

 understood. It enables the cotton plant to remain green and 

 thrifty through periods of unfavorable weather. Probably it 



