CALCAREOUS MANURES— PUACTICE. • 97 



or four l)ushels of gypsum to the acre - more than enough to produce the 

 greatest known effect on clover— and to prevent any benefit being derived 

 from a subsequent application of gypsum ; because there being already in 

 the soil more gypsum than could act, no additional quantity could be of the 

 slightest benefit. 



Since the publication of the foregoing part of this chapter, in the first 

 edition, my use of gypsum, on land formerly acid, has been more extended, 

 and the results have been such as to give additional confidence in the prac- 

 tice, and, indeed, an assurance of good profit, on the average of such ap- 

 plications. But still, as before, disappointments, either total or nearly so, in 

 the effect of such applications, fiavo sometimes occurred, and without there 

 being any known or apparent cause to which to attribute such disappoint- 

 ment in the results. 



In 1832, nine acres of the same body of ridge land above referred to, 

 adjoining the piece on which the 1st, 2d, 3d and 4th experiments were 

 made, and more lately cleared, were sown in clover in the early part of 

 1831, on wheat. The next spring, French gypsum was sown at the rate 

 of a bushel to the acre, except on four marked adjoining squares, each 

 about one third of an acre, one of which was left without plaster, and the 

 others received it at the several rates of 2, 3, and 4 bushels to the acre. 

 The whole brought a middling crop, and was mowed for hay, except the 

 square lefl without gypsum, which did not produce more than half as much 

 as the adjoining land where gypsum was applied at one bushel the acre. 

 The products of the other pieces were slightly increased by each addition to 

 the gypsum, but by no means in proportion to the increased quantity used ; 

 nor was the effect of the four bushels near equal to that formerly obtained, 

 in several cases, from 20 bushels of gypseous earth taken from the river 

 bank. Hence it seems that' it was not merely the unusual quantity of gyp- 

 sum applied in this earth, which produced such remarkable benefit ; and 

 we must infer that it contains some other quality or ingredient capable of 

 giving additional improvement to clover. 



Since the first publication of the foregoing passage, (in 1832,) and in ac- 

 cordance with the^views there presented, more than 10 tons of good French • 

 gypsum has been used, in different years arid with less effect, in general, 

 than formerly, in the first few years after the marling. This general dimi- 

 nution, and more frequent total failures, may be owing to the longer time 

 that the land has been marled, and, by the increase of its vegetable sup- 

 plies serving as putrescent n^anure, the land being thereby changed from 

 calcareous to neutral, and perhaps in some cases even approaching to be- 

 ing acid. If this supposition be well founded, then a repetition of the marl- 

 ing would not only be profitable in other respects, but would increase or 

 restore the capacity of the soil to receive benefit from gypsum. 



The following are my views of the general causes of the inertness and 

 worthlessness of gypsum as manure, on all acid soils, and for the different 

 and valuable results from gypsum, after the soils have been made calcareous. 



I do not pretend to explain the mode of operation by which gypsum pro- 

 duces its almost magical benefits ; it would be equally hopeless and ridicu- 

 lous for one having so little knowledge of the successful practice to at- 

 tempt an explanation, in which so many good chemists and agriculturists, 

 both scientific and practical, have completely failed. There is no operation 

 6f nature heretofore less understood, or of which the cause, or agent, 

 seems so totally disproportioned to the effect, as the enormous increase of 

 vegetable growth from a very small quantity of gypsum, in circumstances 

 favorable to its action. AH other known manures, whatever may be the 

 nature of their action, require to be applied in quantities very far exceed- 



