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 (S03) per
cent.; one per cent. of sulphuric acid is equal to 1.7 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 oy 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