1. Although agricultural production can be increased by use of machinery such as tractors and the addition of fertilizer, the land ultimately can produce only so much food and no more.
    虽然使用拖拉机等机械以及施用化肥可以提高农业产量，但是土地最终所能产出的粮食只有那么多，不会再增加。

2. Farmers add fertilizer to the soil to make plants grow better, or spray poison to kill plant pests.
    农民为了使作物长得更好而给土壤施化肥或者为了杀死害虫而喷撒农药.