CONTINUED EFFECTS OF MARL. 193 



I ascribe to, and shall claim for, calcareous manures; nor are these 

 facts presented for that purpose. Still, even this comparatively short 

 experience shows an undiminished duration of benefit from calx- 

 ing, which is long compared to that of any other manuring. And, 

 therefore, for practical instruction, these and other like facts, if 

 brought from other sources, may be of more- use than any reason- 

 ing upon theoretical grounds, though going to prove a degree of 

 duration of calcareous manures immeasurably greater than any ex- 

 perience of man. 



At this time of my writing (1852), thirty-four years havo 

 passed since my first application of marl (in January 1818), and 

 which was the beginning of regular and continued labours in the 

 same way. The dressings given in 1818, and also in 1819, were 

 all very light ; and were soon inferred to be insufficient, even for 

 the immediate wants of the land. Therefore, more marl was added 

 to all these places, with the next succeeding tillage crop. This 

 early repetition prevented any observation of the oldest dressings, 

 as to their separate and continued effects. In 1820, my error as 

 to quantity was in the opposite extreme, the marl being then laid 

 on so heavily as to produce injury to the crops, after some years. 

 For these different reasons, the marling for the corn of 1821 is the 

 oldest of my applications which was both heavy enough, and not 

 so excessive as to cause any subsequent abatement (by disease) of 

 the increase of crops produced in the first few years. No second, 

 marling has there been given. The crops were increased always 

 in the first year after the marling ; and continued to show more and 

 more increase for ten or more years afterwards. Nor has there 

 been any known diminution of the highest productive power thus 

 obtained, to this time, in thirty-one years of tillage and rest, ac- 

 cording to the rotations in use, since the first marling. These re- 

 marks apply especially and strictly to the eleven acres of newly 

 cleared (and then poor and acid) land, forming the subject of ex- 

 periment 1 (page 117 of this edition) ; and the like results, 

 though for different shorter times, have been experienced on the 

 adjoining and similar land, subsequently cleared and marled, 

 to the amount of eighty or ninety acres. Of nearly all the other 

 lands, also marled, on Coggins farm, for crops of 1821, or soon 

 after, of different soils and conditions, the same statements should 

 be made, in respect to there having been no known abatement of 

 the early increase of crops. To this general rule there are two 

 limited exceptions, apparent or real. The first has just been ad- 

 verted to, and was before described at length (p. 155). This injury, 

 by disease, however great, was not at all a diminution of effect of 

 the marl, but the result of excess of quantity, and of improper 

 effect. With time, and supplying vegetable matter in proportion, 

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