[u]Potatoes sweet potatoes arrowroot Jerusalem artichokes parsnips turnips swedes[/u
Build up organic materials in the soil.
Need perfect drainage.
Moderate nitrogen requirements (not too much or it will just turn into leaves with not much bulb/root).
Adequate supplies of phosphorous potassium and trace elements essential and can be got from aged manure and seaweed rock phosphate sulphate of potash.
Good to cycle after crops of leafy crops such as lettuce or spinach)