318 SOUTHERN FIELD CROPS 



supply all the phosphoric acid removed in a crop of seed 

 and lint of the size indicated. 



In fact, such figures give no idea of the amounts and 

 kinds of fertilizer actually found to be advantageous for 

 the cotton plant. For example, in practice the usual 

 amount of acid phosphate is at least 120 to 200 pounds per 

 acre, which supplies several times the amount of phos- 

 phoric acid removed by seed and lint in a crop yielding 300 

 pounds of lint. The necessity for applying much larger 

 amounts of phosphoric acid than apparently required by 

 the composition of the cotton plant is largely due to the 

 fact that a large proportion of the phosphoric acid is con- 

 verted in the soil into compounds that are not promptly 

 available. 



Means of determining the fertilizer required by cotton 

 on different soils are discussed in succeeding paragraphs. 



284. Phosphoric acid. There are no indications either 

 from the appearance of the soil or from the appearance 

 of the plant as to whether phosphoric acid is needed. 

 However, in regions where the use of commercial fertilizers 

 for cotton is general, experiments and experience have 

 indicated that the need for the application of phosphates 

 is almost universal. Usually a fertilizer for cotton should 

 contain more acid phosphate than any other single chem- 

 ical fertilizer. 



285. Potash. In determining the probable require- 

 ment of cotton for potash, note should be made of the 

 proportion of clay or silt compared with the proportion of 

 sand. Clay and silt are frequently formed from materials 

 rich in potash ; hence the more clay or silt the soil con- 

 tains, the less, as a rule, is the need for potash. 



