Note 51 — Chapter VIII · SOIL AND SUBSOIL.
Reading edition
Hilgard and Jaffa. On the Nitrogen-content of Soil-humus in the Humid and Arid regions. Rep. Cal. Exp’t Station for 1892-4; Agric. Science, April, 1894; Wollny’s Forsch. Geb. Agr. Phys., 1894.