Participating in the Carbon Farming Solution by Eric Toensmeier, study group here on permies.com, I discovered that this book has no glossary. Admittedly, I'm out of date when it comes to textbooks, so this might be common practice these days. However, I think it would really help if we were all working from the same definitions.
Let's make our own glossary.
Whenever we find a word or term we aren't familiar with, let's record it here with the definition that Toensmeier gives.
I expect to be talking about two related subjects, which are often confused (and I'm as guilty of this as any because I've had so much trouble with explaining the difference in the past and simply conflated the two, because it was easier). Understanding the distinction is going to be crucial for understanding the discussion. I know the difference, but there have been a lot of issues with false conflation. It's time we sorted it out. I'm not using Toensmeier's definitions, but these are carefully defined in ecology and agronomy.
Net primary productivity (NPP)
is defined as the net flux of carbon from the atmosphere into green plants per unit time. NPP refers to a rate process, i.e., the amount of vegetable matter produced (net primary production) per day, week, or year.
(also known as "agricultural output") refers to both the measure of the yield of a crop per unit area of land cultivation, and the seed generation of the plant itself (e.g. if three grains are harvested for each grain seeded, the resulting yield is 1:3).
I'll be using the term "yield" mostly in the first sense. If I find myself needing to use the latter, I will say so.
The Yield is one subset of NPP.
The concept of a yield in permaculture is broader, and ill-defined, so if I use the term in this sense I will endeavour to be clear about what I'm talking about.