The answer is D) desertification and deforestation
To know the answer you can rule out the non-possibilities. A is not correct because farmers use them all the time. B is not correct because water and pesticides can flow downstream and carry and deposit sediment. C is not correct because farmers can flood their own farms. When they plant things and a food comes, all of those plants will die or their roots will detach which lowers the food that can be sold. D is correct because farmers don't farm in the desert or the forest, so it would not be an impact of farming.