64 Agricultural Chemistry. 



loss will vary greatly with the nature of the soil. When the land 

 is under crop this loss of nitrates by drainage is greatly reduced, 

 these being constantly taken up by the roots and employed as 

 plant food. In an experiment at Grignon, France, the yearly 

 loss of nitrogen per acre on a soil bearing rye grass was but 

 2.3 pounds. 



The losses of calcium carbonate vary considerably, dependent 

 upon the nature of the soil. From soils of igneous origin its 

 amount has been estimated at 500 pounds per acre per year, 

 while from limestone soils the loss has been estimated at as much 

 as 2700 pounds per acre. The amount lost is increased when 

 ammonium compounds are used as fertilizer. 



The loss of phosphoric acid is probably very small, except in 

 the case of peaty soils, which though often very deficient in this 

 constituent generally lose much in the drainage. This is prob- 

 ably due to the presence of vegetable acids and carbon dioxide 

 produced by the decay of organic matter, which would intensify 

 the solvent action of water. German experiments report an 

 annual loss per acre of from about 8 pounds for clay soils to 

 19.6 pounds for peaty soils. 



The loss of potash is variable, but small in amount. From ex- 

 periments at Rothamsted, the annual losses in potash per acre 

 were found to vary from 3 to 12 pounds. The losses of sulphur 

 by drainage from soils may be considerable. At Rothamsted it 

 was found that about 50 pounds per acre per year of sulphur, 

 calculated as sulphur trioxide, escaped into the drainage water. 



Highly manured land will sustain larger absolute losses of 

 plant food than lands in an average state of fertility. 



Soil as a source of plant food. The proportion of plant food 

 present in soils' is very small even when the soil is extremely 

 fertile, the bulk of the soil serving as a support for the plant and 

 as a sponge to hold the water. Many chemical analyses of soils 

 have been made and these show a considerable variation in the 

 composition of soil. A good arable loam may contain 0.15 per 

 cent of total nitrogen, 0.15 per cent of total phosphoric acid, 



