FERTILIZERS, ROTATIONS FOR COTTON 89 



It also contains considerable quantities of magnesium 

 suKate and magnesium chloride. It is highly probable 

 that part of the effect produced from adding kainit is due 

 to the stimulating effects of these magnesium salts. 



Muriate of potash and sulfate of potash are high-grade 

 materials containing approximately 50 per cent of actual 

 potash. For this reason it often happens that potash ca;n 

 be purchased cheaper in these materials than in kainit 

 because of the decreased freight rate a unit of potash 

 secured. All of these potash fertilizers have been secured 

 from extensive salt deposits in the region of the Harz 

 Mountains in northern Germany. 



98. Need of cotton soils for potash. — Soils of the 

 cotton-belt are in less need of potassic fertilizers than of 

 phosphatic or nitrogenous materials. The principal rea- 

 sons for this are: (1) these soils, in-general, contain larger 

 natural supplies of potash than of nitrogen or phosphoric 

 acid; and (2) in ordinary farm practice the stalks of cotton, 

 corn, and the like which contain most of the potash 

 taken up by the crop are more often returned to the soil 

 than the seed or seed products, which contain most of 

 the nitrogen and phosphoric acid. 



The sandy soils and often the sandy loams are usually 

 deficient in potash and consequently respond profitably 

 to potassic fertilizers. Clay soils, owing to the fact that 

 they have been produced largely from the weathering of 

 potassic feldspars are usually rich in potash. 



99. Potash fertilizers check rust. — Experience has 

 shown that potash fertilizers often greatly decrease the 

 injury produced by cotton rust. As to whether this is 

 due to a fungicidal action of the potash or whether it 

 merely gives the cotton plants greater power of rust- 

 resistance is not known. It seems to help the plants to 



