I need some clarification on this addage. Are you saying that a pint
f sand is going to weigh the same as a pint of peat? I think my
weekly feed picked up some weight after I made it up as it has
absorbed a lot of moisture. If I put it on the scales to weigh out a
pound for weekly feed purposes is it going to affect the nutrients my
plants are getting or do I need to apply the WF based on volume and
forget about the actual weight?
I really appreciate the insightful study, which leads to such good questions from you, Dave, as well as from several others. This helps us all to learn and be better gardeners.
The statement "a pint is a pound the world around" is obviously not strictly accurate, and is quite inaccurate when applied to the comparison of dirt and sawdust, and other very dissimilar materials.
I didn't coin the phrase, and so can't know for sure the motivations behind it. However, I have noticed that all around the world tin cans are available that hold about the same amount of material. In America it's 1 pint, or 16 fluid ounces, and in other countries, where the metric system holds sway, it is a 450 gram can that is essentially the same size.
You'll be purchasing your fertilizers by weight, and if you have a scale it's certainly best to weigh each component when mixing, In fact if you were adding all of the micro's individually you would end up using much more than necessary of a couple of them if you were to use volume measurements instead of actual weight, because they are very heavy.
If all you have access to is measuring cups and pint-sized cans, and if you are combining compounds, such as the pre-mixed micro-nutrients from the Foundation, you won't be off far enough to ruin your garden.
When applying materials to your garden you can use volume measurements without worrying. And if your fertilizers ever get wet it's especially beneficial to use the volume, because of the substantial difference in weight between wet and dry fertilizers.