_The Nitrogen-Content of Humus._—Since soil-humus is doubtless the chief depository of soil-nitrogen, and the main source from which, through the process of nitrification, the nitrogen-supply to plants is usually derived, its content of that element is a matter of great interest. It has been customary to estimate approximately the nitrogen-content of soils by the proportion of humus-substance present; and as the light tints of the soils of the arid region indicate a small humus-content, a scarcity of nitrogen seemed to be also indicated for these lands. As this in a number of cases did not seem to accord with actual experience, an investigation of the subject was made at the California experiment station,[51] with the results shown in the subjoined table. In considering these results it must be kept in mind that while arid conditions can rarely be fulfilled in the humid region, humid conditions are quite frequently locally represented in the arid, in lowlands and on high mountains; while moderately moist benchlands represent the semi-arid regime. [51] _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. HUMUS PERCENTAGE AND NITROGEN CONTENT IN SOILS OF THE ARID AND HUMID REGIONS. =====+==============================================+=====+========+======== | |Humus|Nitrogen|Nitrogen Station| Soils arranged in order of nitrogen | in | in | in Number| percentages in humus. |soil,| Humus, |soil, | | per | per | per | |cent.| cent. |cent. -----+----------------------------------------------+-----+--------+-------- | SOILS OF THE ARID REGION (California). | | | | | | | 2061 |Dark clay loam, Arroyo Grande Valley, | 3.06| 22.00 | .670 | San Luis County | | | 2291 |Red soil, Orland, Glenn Co. | .71| 21.10 | .150 1904 |Sediment Soil, Porterville, Tulare Co. | .90| 19.50 | .180 1901 |Sandy soil near Ceres, Stanislaus Co. | .64| 18.75 | .120 704 |Sandy soil of plains, near Fresno, Fresno Co. | .60| 18.66 | .112 6 |Black adobe soil, Stockton, San Joaquin Co. | 1.05| 18.66 | .196 1679 |Black adobe soil, Berkeley, Alameda Co. | 1.20| 18.58 | .203 2324 |Clay soil of desert, Imperial, San Diego Co. | .38| 18.40 | .070 1167 |Black clay loam soil, near Tulare, Tulare Co. | 1.66| 18.19 | .302 1536 |Brown loam soil, Windsor Tract, Riverside, | .20| 18.00 | .036