Here are some tips for growing turnips:

Site, soil type:

Turnips like loose and quite fertile soil.   Turnips prefer cool weather.

They benefit from partial shade in summer.

Planting requirements:

Turnips can be planted early, as soon as the ground can be worked.    Turnips are frost tolerant.

Sow seeds ¼ inch deep and eventually thinning to 5 inches apart.

Row cover will help warm the soil and seeds for quicker germination.

Nutrition/Fertilizer needs:

Add one cup of complete organic fertilizer per 10 feet of row.

Water needs:

Keep soil moist at all times for healthy plants.

Other tips:

Turnips can be bothered by flea beetles, disfiguring the leaves but not affecting the roots.  Use row cover if this is a problem.

Root maggots can be prevented with a row cover installed on the day of planting.

For a great vegetable treat, grow Hakurei.  They are sweet and fruity.