SUPPOSED PROGRESS OP ACTION. . 219 



product had risen from ten to thirty bushels of corn to the acre. 

 The soil has then become neutral. It can never lose its ability 

 (under the mild rotation supposed) of producing thirty bushels ; 

 but it has no power to rise above that product. Vegetable food 

 for plants continues to form, but is mostly wasted, because the 

 salts of lime are already combined with as much as they can act 

 on ; and whatever excess of vegetable matter remains in the soil, 

 is kept useless by acid also newly formed, and left free and noxious 

 as before the application of calcareous earth. But though this 

 excess of acid may balance and keep useless the excess of vegeta- 

 ble matter, it cannot affect the previously fixed fertility, nor lessen 

 the power of the soil to yield its then maximum product of thirty 

 bushels. In this state of things, sorrel may again begin to grow, 

 and its return may be taken as notice that a new marling is needed, 

 and will afford additional profit, in the same manner as before, by 

 destroying the last formed acid, and fixing the last supply of vege- 

 table matter* Thus perhaps five or ten bushels more may be 

 added to the previous product, and a power given to the soil gra- 

 dually to increase as much more, before it will stop again for 

 similar reasons, at a second maximum product of forty or fifty 

 bushels. I pretend not to fix the time necessary for the completion 

 of one or more of these gradual changes ; but as the termination 

 of each, and the consequent additional marling, will add new pro- 

 fits, they ought to be desired by the farmer, instead of his wishing 

 that his first labour of marling each acre may also be the last re- 

 quired. Every permanent addition of five bushels of corn, to the 

 previous average crop, will more than repay the heaviest expenses 

 that have yet been encountered in marling. But whether a second 

 application of marl is made or not, I cannot imagine such a con- 

 sequence, under judicious tillage, as the actual decrease of the 

 product once obtained. My earliest marled land has been severely 

 cropped, compared to the rotation supposed above, and yet has 

 continued to improve, though at a slow rate. The part first marled, 

 in 1818, had only four years of rest in the next fifteen; and 

 yielded nine crops of grain, one of cotton, and one year clover 

 twice mowed. This piece, however, besides being sown with 

 gypsum (with little benefit), once received a light cover of rotted 

 corn-stalk manure. The balance of the same piece of land (Exp. 

 1) was marled for the crop of 1821 has borne the same treat- 

 ment since, and has had no other manure, except gypsum once 

 (given in the natural gypseous earth found on the farm),* in 1830, 

 which acted well. These periods of twelve and fifteen years (even 

 though now extended to and confirmed by nine years more of ex- 

 perience) are very short to serve as grounds to decide r n the 



* See accounts of this bed of "gypseous earth" in vol. 1 of Farmers' 

 Register, and of its effects, in success and failure, in vol. 10. 



