SULPHATE OF LIME IN ESSEX SOILS AND SUBSOILS. 



63 



through the superficial layers in order to replace water evaporated 

 from the surface soil. When this occurs the sulphate of lime is 

 left behind, either as an efflorescence on the surface or, it seems 

 possible, as crystals of selenite in the subsoil. 



In considering the source of the sulphate of lime in shallow 

 wells and superficial strata of the London-clay, it will be necessary 

 to enquire to what extent sulphate of lime exists in the surface 

 soils of Essex. In conjunction with my former colleague, Mr. 

 Frank Hughes, now of the Khedivial Agricultural Society of 

 Egypt, I analyzed for sulphate some twenty Essex soils. The 

 results of these analyses are expressed as sulphuric acid (SO s ) per 

 cent. ; one per cent, of sulphuric acid is equal to 17 per cent, of 

 sulphate of lime. 



Taking the top 9 inches of soil to weigh 3,000,000 lbs. per 

 acre, the average quantity of sulphate of lime in the surface soil 

 amounts to 2,610 lbs. The drainage through naturally or 

 artificially well-drained land in a year of average rainfall in 

 Essex probably amounts to 150,000 gallons per acre. From 

 analyses of surface drainage waters the sulphate of lime contained 

 in such a quantity of drainage water would amount to nearly 

 200 lbs., so that in a period of thirteen years the whole of the 

 sulphate of lime would be exhausted. 



Sulphate is as necessary an ingredient of plant food as 

 phosphate. Taking the average produce of an Essex farm, an 

 amount of sulphate will be used by crops each year equal to 44. 

 lbs. of sulphate of lime per acre. The question may well be 

 asked whether, in view of the exhaustion by drainage of the 

 sulphate of the soil, Essex soils are not deficient in this ingredient 

 of plant food. A series of field experiments have been carried 

 out_by the Essex Education Committee on the subject, but it 



