VI.] INTERPRETATION OF ANALYSIS 189 



be taken to liberate some of the reserves, as by 

 the judicious use of lime or of organic manures which 

 will generate carbonic and other acids within the 

 soil. 



Rainfall and water supply are important factors in 

 determining the choice of phosphates ; basic slag proves 

 less useful than superphosphates on dry soils ; but at 

 least as useful on moister soils or under higher rainfall. 

 The amount of calcium carbonate in the soil is not the 

 determining factor, but the water supply; if, as often 

 happens, a chalky soil is dry, superphosphate will prove 

 the more useful ; where the rainfall is greater, basic slag 

 is as good. In all cases where much purchased food is 

 fed upon the land, phosphates are of advantage to the 

 succeeding crop, and on all wet cold soils, a free supply 

 of phosphates aids in the early maturity and ripening of 

 the crop. 



The need' of soils for potash depends even more 

 upon the water supply. On a dry soil crops are likely 

 to cease growing, and ripen much faster than in a 

 moister district. Now, potash manures tend to prolong 

 the vegetative development of a plant, and in a dry 

 district, or on a dry soil, will keep it growing after it 

 would otherwise have stopped ; in consequence, they 

 give increased, if later, crops. Other things being 

 equal, dry soils are more likely to respond to potassic 

 manuring than others better supplied with moisture, 

 but no richer in available potash. In reclaiming the 

 very dry heaths of the Eastern Counties, the production 

 of profitable crops depends upon a liberal and regular 

 use of potash manures. 



No sequence has ever been traced between the 

 content of the soil in oxide of iron and its fertility. 

 The red soils of Great Britain, which are often of high 

 repute, may show less than the usual proportion of 



