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is especially the case iii poor sandy soils, and a good dose of lime or 

 marl, followed by barn-yard manure or guano has a most beneficial ef- 

 fect. By this means the valuable portion of the manure or guano, the 

 ammonia, potash, and phosphoric acid, are retained in fhe land, whilst 

 the others combine with the lime and are gradually washed out. 



Ferric oxide is found in all soils, and causes the reddish color so very 

 common in a great many of them. To its presence is chiefly due the 

 retention of the phosphoric acid, an insoluble basic phosphate of iron 

 being produced. On its state of oxidation depends its favorable influ- 

 ence on the soil, that of ferric, sesqui, or per oxide, better known as the 

 red rust of iron, being the most suitable. In its less perfectly oxidized 

 forms, which are, however, soluble in organic acids, it exists very often 

 in the subsoil, and becomes peroxidized on exposure to the air. Its ac- 

 tion is both physical and chemical. The preference of farmers for " red 

 lands. " arises from their experience of its beneficial action in the soil. 



From 1.5 to 4 per cent, of ferric oxide is ordinarily found in soils 

 but slightly tinted. Ordinary ferruginous loams vary from 3.5 to 7 

 per cent., highly colored " red lands " have irom 7 to 12 per cent., and 

 occasionally 20 per cent, and more. The efficiency of the ferric oxide 

 depends upon its mechanical condition ; when encrusting the grains of 

 sand, or occurring as nodules, whilst the chemical analysis inaj show a 

 large percentage of it present, it exerts little or no influence upon the 

 soil, but when in a state of fine division these advantages are realized. 



Soils containing a large percentage of ferric oxide have generally a 

 low percentage of organic matter, but, notwithstanding, are as a rule 

 very fertile. In clay lands especially its presence is very beneficial as 

 tending to made them easier for tillage ; its color tends to the absorp- 

 tion of heat and of oxygen. Such soils, however, suffer from floods or 

 bad drainage, the ferric oxide becoming reduced under such circum- 

 stances to the ferrous state. (Hilgard.) 



Phosphoric acid is contained in all good soils, but in very small quan- 

 tities when compared with the other principal ingredients, and exists 

 in combination with lime, iron, and alumina, phosphate of lime being 

 its most common form. In general, even in the most fertile soils, it is 

 found in very minute quantities, on an average less than a half per cent.; 

 in clay lands this may rise to 1 per cent. Its value in fertilizers de- 

 pends on its state of combination, whether it is soluble and immediately 

 available for plant food, as the superphosphates, or slowly soluble, 

 like the lime phosphates, forming a reserve store of food for the future. 

 It occurs in all soils that have been formed from such rocks as the gran- 

 ites, gneisses, limestones, and dolomites, which contain it without excep- 

 tion; volcanic soils possess it in large quantity, whilst alluvial soils and 

 those lands that are periodically swept by floods are much poorer. 

 Soils containing less than 0.05 per cent, of it will be sterile and unfer- 

 tile, as a general rule, unless accompanied by a large amount of lime. 



