Nature-Study Agriculture 



Super- 

 phosphate 



Potash 



Potash- 

 loving 

 crops 



Sources of 

 potash 



Why lime 

 may be 

 lacking 



material is treated with sulf uric -acid. It is then called. 

 " acid phosphate " or " superphosphate." The acid that 

 is used is neutralized by the lime in the bone or rock, so 

 that it does no harm to the soil. 



Potassium. There are large quantities of potassium 

 in the soil, but it is always in compounds. And most 

 of these are so insoluble that the plants 'cannot benefit 

 by them. For this reason it is often necessary to fer- 

 tilize the ground with soluble potash compounds, which 

 the plants can readily absorb. 



Clover and the other leguminous crops need potash, 

 and fruit trees in bearing should be well supplied with 

 it. More than half of the mineral matter of fruit is 

 potash. The potato, also, is a potash-loving plant. 



To obtain potash as a fertilizer, the simplest method is 

 to use wood ashes. (Exp. 4.) But the supply of these 

 ashes is very limited, and coal ashes do not contain 

 enough potash to make them of any value. The chief 

 commercial source of this fertilizer is a vast deposit of 

 various potash salts near Stassfurt, Germany. During 

 the war we could not get German potash, and for that 

 reason began to develop our own potash resources. 

 Most of the home supply has been obtained from the 

 brine of salt lakes in Nebraska, Utah, and California. 



Lime. In nearly all regions of heavy rainfall, lime, 

 which is somewhat soluble, is likely to be deficient in 

 the soil (Fig. 137). In such places crops would be 

 greatly benefited by its use. Lime is applied rather to 

 improve the soil than to supply a plant-food material, 

 though it serves both purposes. 



When used on soils that need it, lime has the follow- 



