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T H E JOURNAL, OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y .
hydride expressed on the basis of humus, it will be seen in a general way that as the amount of humus decreases the percentage of phosphoric anhydride in the humus increases (see Table 11). Arranging the soils in groups of three, and averaging the percentages just expressed, this fact is brought out more strikingly (Table 111). These results suggest the possibility that phosphorus in humus is not made available to plants as the humus decomposes, but rather that the phosphorus once in the humic form is unavailable to plants. This point is to be tested on comparable virgin and cropped samples of soils, and in addition further work is contemplated on the changes taking place in a soil during its period of cropping. Acid and non-acid soils will be used, these same soils so far as possible, but the study will be made on the differences that exist in the phosphate compounds between the virgin and the cropped samples. TABLE111. HUMUSAND PHOSPHORIC ACIDIN HUMUS. AVERAGED IN GROUPSOP THREE.
..... . . . . . ... , . . .. .
Humus PnO,in humus
........... . .
1.27 0.93
0.69 2.06
0.48 2.68
0.21 4.17
Summarizing the results, i t is to be observed: First, that acid soils lack available phosphates. Second, that soil acidity seems to cause a lack of available phosphates, since acid soils contain a higher percentage of their total phosphoric acid in iron and aluminum form and less calcium phosphate than do non-acid soils, and particularly a greater ratio of iron and aluminum phosphates t o calcium phosphate. This does not mean that non-acid soils may not be lacking in available phosphates, due to some other cause. Third, that the figures on humus and phosphoric anhydride in humus show an interesting variation, suggesting that humic phosphorus may be unavailable to plants. Fourth, that fifth-normal nitric acid is an excellent indicator of soil needs with respect t o phosphates, due t o the fact that it determines the amount of calcium phosphate in soils. If a soil, in Wisconsin a t least, falls below 0.015 per cent. of phosphoric acid soluble in fifth-normal nitric acid, it will respond to phosphate fertilizer. DEPARTMENT OF SOILS, AGRICULTURAL EXPERIMENT STATION, UNIvsRSlTY OF WISCONSIN,
A REMARKABLE ACCUMULATION OF NITROGEN, CARBON AND HUMUS IN A PRAIRIE SOIL. BY F. J. ALWAYAND
c.
E.
VAIL.
Received November 14, 1908.
Lawes and Gilbert’ in 1885 reported the analysis of a sample of soil from Selkirk, Manitoba, showing 0.618 per cent. of nitrogen in the first foot. This has since been commonly used by writers as an illustration of the extent to which nitrogen may accumulate in virgin prairie soils. “The soil from Selkirk was taken from a farm which had been in cultivation for 2 5 years, but from a portion near the buildings which had never been broken up.” Lawes and Gilbert, neither of whom had seen the farm, recognized the remarkable composition of the sample b u t evidently considered it representative of the soil area. The explanation of the composition of the sample may, however, be the same as that of the still higher percentages in the case of some samples taken by the senior author of this article from near Indian Head, Saskatchewan, in October, 1907. Selkirk is situated in the bed of glacial Lake Agassiz,* now the so-called Red River Valley, the soil being a lacustral clay. The conteniporaneous glacial Lake Saskatchewan3 covered a considerable area in what is now the province of Saskatchewan, which adjoins Manitoba on the west. The characteristic soil covering its bed is likewise a lacustral clay. The soils of these two areas, being formed from similar sources and at the same time as well as having since been subjected to more or less similar climatic conditions, may reasonably be expected to have many characteristics in common. A considerable number of individual samples were taken from a tract of virgin prairie adjacent to the Indian Head experimental farm in order to be able to form some idea as to the differences in composition between the surface soils of the two types before they were brought under cultivation. All the samples were taken with a brass tube 1-3/8 inches in diameter, provided with a wide collar six inches from the end. The tube was driven into the ground until the collar rested firmly on the surface of the soil. Two types of soil occur both in the prairie tract and on the experimental farm, viz., boulder clay Cham. Soc., 1886, Proc.. pp. 380-422. Upham. Lake Agussia, U.S.Geol. Survey, 1886.
1 Jour. 2
* Ibid.
‘
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y . or till as well as lacustral clay. Both types have previously been described. The most clayey parts of the latter, which also form the lowest lying portions, are characterized by small hummocks two or three feet in diameter and about six inches high. These hummocks are often not noticed until one drives over the prairie in a carriage. They are probably similar in origin t o the "hogwallows"2 of the southwestern United States. Three individual samples were taken &om the till, three from the summits of the hummocks and three from the rifts at the edges of the latter. Besides these nine samples, four were taken from modified rifts and divided into one-inch sections,
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the summits of the hummocks, it not being suspected that there would be found the great differences between the two which the analyses have since revealed. The humus was determined by Grandeau's method as modified by Hilgard. To determine the humus nitrogen the ammoniacal solution of humus was evaporated t o a small volume, magnesium oxide added, the solution boiled again and the nitrogen in the residue finally determined by the usual Kjeldahl method. The organic carbon was determined by combustion with copper oxide. There are no marked differences in composition between the till and the soil from the summits
RESULTS OF THEANALYSES.
Soil
Humus. Per cent. 2.73 3.08 2.71
NO. Boulder clay.
7 14 715 716
'
