That may be so, but with all respect, the fact that Tolkien does not mention elven agriculture does not imply that he simply didn't bother to tell us but that it must have existed anyway. Elven life seems very much at harmony with nature. Maybe it would be against Elven nature to hold an animal captive against it's will, or even crops, but rather gather the fruits of free living plants, maybe enhancing their qualities by their skills. After all, Lembas were not large or heavy, yet very nourishing. Maybe such food was sufficient to feed elves, enhanced by fruits and berries. Lembas itself could be made from the grains of free plants found in the woods.