Note 109 — Chapter XI · THE ORGANIC CONSTITUENTS OF THE SOIL SOLUTION.
Reading edition
Mr. J. G. Smith has made a comparison between the potash and phosphoric acid content of the wheat and following crop of ragweed grown on a farm in Fairfax Co., Va. His unpublished results, with some others found in the literature, are given in the following table:
Material Potash K₂O % Phosphoric acid, P₂O₅ % Analyst
Wheat 0.76 0.52 Smith
Young ragweed 1.78 0.73 Smith
Ragweed in seed 1.28 0.35 Smith
Ragweed in seed and
accompanying plants 1.18 0.39 Smith
Winter wheat in flower 1.796 0.51 Wolff’s tables in Johnson’s
“How Crops Grow,” p. 376.
Ragweed 1.79 0.41 DeRoode,in Bull. 19, W. Va.
Agr. Exp. Sta., 1891
Ragweed 1.809 0.54 Burney, 2d. Ann. rept.
S. C. Stat., 1889, p. 146
On the whole, ragweed seems to require and take from the soil about as much mineral matter as does wheat. It is stated by some of the dairy farmers near Washington, who cut the mixture of ragweed, other weeds and grass following wheat, for a hay crop, that the weight of the ragweed crop is generally heavier than that of the wheat crop. Therefore the ragweed actually removes more mineral matter from the field than does the wheat. These facts lend no support to the popular notion that wheat “exhausts” the soil of its “available” mineral plant nutrients. For analyses of a number of common American weeds, see Analyses of the ashes of certain weeds, by Francis P. Dunnington: Am. Chem. Jour., 2, 24-27, (1880).