134 EFFECTS CONTINUED. 



The crops of wheat were throughout less injured by the excess 

 of marl than the corn. 



For the crop of 1828, ploughed with three mules to each plough, 

 from six to seven inches deep seldom turning up any sub-soil 

 (which was formerly within three inches of the surface), and the 

 soil appearing still darker and richer than when preparing for the 

 crops of 1824. The ploughing of the square not marled (A) no- 

 where exceeded six inches; yet that depth -must have injured the 

 land, as I can impute to no other cause the remarkable diminution 

 of product, through four courses of the mild four-shift rotation. 

 It was evident that a still greater depth of furrow was not hurtful 

 to the marled land. A strip across the field, in another place, was 

 in 1828 ploughed eight inches deep for experiment, by the side of 

 another of four inches, and the corn on the deepest ploughing was 

 the best. Another strip was trench-ploughed twelve inches deep, 

 without showing any perceptible difference, either of product or in 

 the effects of damage from the excess of marl. 



This square left without marl was the land previously referred to 

 (page 44) as showing a diminished product through three succes- 

 sive courses of the rotation recommended bv- the author of f Arator' 

 as enriching. Since, another crop has been made and measured, 

 and found to be still smaller than any previous. To whatever 

 cause this continued falling of, for 16 years, may be attributed, it 

 is at least a remarkable contradiction to the doctrine of vegetable 

 matter serving alone to make poor land rich. 



Much trouble has been encountered in attending to this experi- 

 ment, and much loss of product submitted to, since its commence- 

 ment, for the purpose of knowing the progress and extent of the 

 evil caused by the excess of marl. But another portion of the 

 field, marled as heavily in 1824, and where equal damage was ex- 

 pected to ensue, has been entirely relieved by intermitting the corn 

 crop of 1828, sowing clover, which (by manuring with gypseous 

 earth, or green-sand earth, at 20 bushels to the acre) produced 

 well, and which was left to fall and rot on the land. The next 

 growth of corn on this part of the field (1832) was free from dis- 

 ease, and though irregular, seemed to the eye to amount to full 

 twenty-five bushels to the acre. 1835.] 



[After 1836, the rotation and management of this field ceased 

 to be regular or uniform, as previously ; and also, by cross plough- 

 ing, &c., during so many years, marl had necessarily become 

 slightly diffused over the space designed to remain without marl. 

 Therefore no more measurements were made, as they could no 

 longer be relied on for accurate comparison. The unmarled part, 

 even with its slight accidental gain of marl from the surrounding 

 ground, and half the piece having also been dressed with putres- 

 cent manure in 1832 (as stated above), is but very little improved 



