He says that is because the farmer used rich soil to produce the sod, so it might not do well in clay soils.

VOA: special.2009.07.07

Soil was being eroded and wasted along the Eastern seaboard, and they were using up the great soils of the Mississippi Valley and over time that slave system just somehow wasn't going to work out.

东部沿海地区的土地因被侵蚀而荒废掉,密西西比河谷地区的土地资源即将被耗尽,但就在这种情况下,奴隶制依然能维持南方的经济

耶鲁公开课 - 美国内战与重建课程节选

In June,students at the Agroecology Summer Intensive Program begin taking courses like Introduction to Soils.

VOA: special.2009.04.14

Cindy Haynes says little or no fertilizer is needed in fertile soils.

VOA: special.2009.02.17

She says that the goods and services provided by nature - like clean air, rain or fertile soils - should not be taken for granted.

VOA: standard.2010.02.24