The Weight Of Soils

This depends upon their composition and compactness. It is of interest to the farmer chiefly as an indication of the amount of vegetable matter that a soil contains, because this influences its value for cropping. The coarser the grains, the heavier the soil; humus makes a soil lighter. A heavy soil — one weighing over 80 lbs. per cubic foot — is likely to be benefited by the addition of humus. As the term is commonly used, however, a heavy soil is one that is tenacious, and refers to texture, not to weight. Schubler gives the average weight of a cubic foot of dry soil as follows :
Sand 100 lbs.
Garden Soil rich in humus 70 lbs.
Peat Soil 30—50 lbs.

The weight of the soil on an acre of land is so great that if a very small percentage of it is plant food this may amount to a very large quantity per acre. An acre of clay loam, nine inches deep, weighs about 3,000,000 to 3,500,000 lbs. Suppose this soil contains only one-tenth of one per cent, of nitrogen, which is an average amount of that plant food; the acre would contain, in the first nine inches only, 3,000 to 3,500 lbs. of nitrogen. Compared with this amount, the 30 to 75 lbs. of nitrogen that we apply as a fertiliser to an acre of impoverished land is a mere bagatelle.