Work the soil to a depth of 18 inches if possible. This allows good root and tuber development. Some humus can be very beneficial for potato production. Potatoes prefer slightly acidic soil, alkaline soil can lead to somewhat scabby potatoes. Potatoes respond to calcium and a balanced fertilizer program of nitrogen, phosphorus and potassium.
Some varieties prefer splitting the total nitrogen application.
Consult the varieties profiles for details . If you want to grow organically, working in 100 lbs. In both cases work the fertilizer in well before planting. Fertilizer can also be banded beneath the seed at planting time which works very well in alkaline soils. Potatoes can be planted before the last frost date since their first 25 - 40 days are spent underground protected by the soil from frosts.