The thing we need to remember when comparing feeding a Grow-Bed or Soil-Bed (these terms are used interchangeably) with feeding field crops is that in the garden you are actually feeding 2 rows of plants at a time in a single 18″ bed. So 1 pound of Weekly Feed applied to 30 feet of row is actually feeding 60 feet of plants, since you plant your potatoes 8 inches apart on both sides of the bed, between the ridges.
Beyond that, field crops do not get fertilized as much or as often as garden crops, mainly because it is not practical to do so. In the garden we band the fertilizer in each bed – 4 inches from the plants (right between the two rows in the bed). There are 254 30-foot long beds per acre, so one application would require 254#. That is not much different from the field application rate (240#), and the plants are pretty well-fed if you can band the fertilizers, rather than broadcasting them.
Only 3 applications are given to field crops, because it is impractical to drive a tractor through a field when the plants are fully grown, since many plants would be harmed by the tractor wheels. However, in the garden, we recommend 5 feedings on potatoes, so they ultimately receive almost twice the amount of fertilizer that field-grown potatoes get, and the expected yield is correspondingly higher, which may very well offset the higher labor required.
Just a word about the benefits of Grow-Bed or Soil-Bed gardening: Dr. Mittleider has found that planting two rows of most plants together – about 12 inches apart in the 18 inch bed (the ridges take up the other 6 inches), provides several advantages. First the fertilizer is immediately available to both rows of plants and virtually none is wasted or used to feed the weeds. Second, watering is very efficient, since the ridged level beds keep the water right at the root zone of the plants, and again none is wasted. Third, weeding is much reduced, since no water is applied to the 3 1/2 foot-wide aisles, and the vegetables quickly shade any weeds that might grow in the bed area. The plants grow out into the aisles, so they get plenty of light and air, and the wide aisles make working much easier and more pleasant, without sacrificing productivity.