the earth cursed twice?

12 When thou tillest the ground, it shall not henceforth yield unto thee her strength

How was this different from the curse upon the ground in Gen 3?
Gen. 3:17 "...cursed is the ground for thy sake; in sorrow shalt thou eat of it all the days of thy life;
Gen. 3:18 Thorns also and thistles shall it bring forth to thee; and thou shalt eat the herb of the field;
Gen. 3:19 In the sweat of thy face shalt thou eat bread..."

[b]it shall not henceforth yield unto thee her strength[/b]; the earth had been cursed for Adam's sin, and was not so fruitful as in its original state; and now it was cursed again for Cain's sin; not the whole earth, but that part which belonged to Cain, and was cultivated by him; and so it must be supposed to be cursed, not only in the spot where he had been settled, but in every other place where he should come and occupy, and which through this additional curse became so barren that it did not yield such good fruits, and such an increase of it as before; it lost its native and vital juice, by which seed cast into it became not so fruitful, and did not increase; but instead of this, though much pains were taken to manure it, and much was sown, yet it brought forth little, at least but little to Cain, whatever it did to others; and therefore it is said, "shall not yield unto thee"; it would not turn much to his account, or yield much profit and increase to him, or bring forth much fruit; see Job 31:38.