164 REPOKT OF THE COMMISSIONER OF AGRICULTURE. 



ally contain from 1 to 3 per cent, of the carbonate. Less than 1 per 

 cent, may be regarded as a defective quantity. In the lightest sandy 

 soils the percentage of lime should not fall below .100, in clay loams 

 not below .250, and in heavy clay soils not below .500. Where a soil 

 is deficient in lime, the little there is of it is present in combiEatiou with 

 the organic acids, and is more abundant on the surface than in the sub- 

 soil. It preserves the particles of clay in a separate coagulated condi- 

 tion, and thus allows them to exercise their absorbent powers on various 

 salts, which otherwise would escax)e their action. It also promotes the 

 decomposition of vegetable matter and the formation of nitrates in the 

 soil. 



Most green cro^s are often subject to disease when grown on soils 

 deficient in lime, even when they have been well manured. Up to a 

 certain stage, the cereal or other crops appear to thrive well, but as the 

 season advances they sustain a check and yield a poor harvest. This 

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

 marl, followed by barnyard manure or guano, has a most beneficial 

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

 ammonia, potash, and phosphoric acid, are retained in the 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 x)roduced. On its state of oxidation depends its favoi>able 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 that exist very 

 often in the subsoil, it becomes peroxidized on exposure to the air. Its 

 action 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 from 7 to 12 per cent., and 

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

 depends upon its mechanical condition ; when incrusting the grains of 

 sand or occurring as nodules, whilst the chemical analysis may 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 as a rule, 

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

 tending to make 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. 



Phosphoric add 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 depends 

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

 ble 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 granites, 



