(I am not linked to this site in any way)
I was reading about how to improve yield of plants such as carrots that grow underground (known as root crops), and aside from regular stuff about maintaining the required supply of different nutrients in the soil through rotation, I came across this site (on a forum, there were a couple of people recommending this site, so thought I will pass it on).
The site is called Gardens Alive and this specific page is about the Root Crops fertilizer (link to site).
From the site:
Root crops- such as onions, beets, carrots, potatoes and turnips- need the support of soil that’s rich in potassium and phosphorus. So we’ve packed Root Crops Alive! with these essential nutrients in just the right balance needed by root crops. And, unlike greensand-based fertilizers, the potassium in Root Crops Alive! is plant-based, so root crops benefit immediately.
Apply 2-3 lbs. per 100 sq. ft. when you prepare the soil, or side-dress when plants emerge to get greater coverage per pound. For best results, feed again in midseason.
I do not recommend or dismiss this item, just read about it and thought I will pass it along.