The article said use 3 lbs of 10-10-10 but no other info. per row? per square foot? per acre? per beet?
Application rates are usually per 1,000 sq ft. I'm a big fan of soil testing to find out exact fertilizer needs. Many soils are naturally high in phosphorus and adding more with a balanced fertilizer like 10-10-10 can actually slowly increase phosphorus to harmful levels - harmful to plant growth, not human health. Every state has a cooperative extension service based at your land grant Agriculture school. They do testing for a nominal fee and allow you to designate what you are growing. Results include pH, phosphorus, and potash levels (sometimes more nutrients like magnesium) and how much NPK is needed annually. If phos or potash are low, corrective measures are listed. It is the same if pH is out of acceptable range for the crop. Beets need compost and/or manure added to the soil annually to keep them sweet tasting. Since you have probably already planted, add a top-dressing with 2 inches of compost.