To measure mineral uptake by plants, one could dry then burn the leaf, stalk, and roots. Crucibles & hot flame are used in labs. Salts don't easily burn or melt, but all the products of photosynthesis do. These source from water and CO2, which are released by the burn. White ash is not heavy, and that's the amount of fertilizer salts that were taken up for growth. Organic nutrients must be broken down to component salts by micro beasties like bacteria & such, to become soluble & available to the plant whether the plant uses it or not. Organics are always breaking down, but plants use only what they use.
Medium levels fall from this, and compaction. Mostly compaction
She's a good looking little fat girl, fuzzing up nicely.
Lovely progress from a 'found' seed