Last year I shared an elemental cartogram of relative mineral nutrient amounts in turfgrass leaves. An elemental cartogram is a periodic table of the elements with the area of each element modified by a theme, and in this chart the area is modified by the amount of mineral nutrients.
One thing I notice on the cartogram of mineral nutrients in bentgrass leaves is this: where are the micronutrients? We can see the macronutrients clearly: N, K, and P. Then the secondary nutrients: Ca, Mg, and S. But the micronutrients are in the leaves in such small concentrations that they don't register on this cartogram, in which their quantity is compared to those of the macronutrients and secondary nutrients.
The quantity of an element required as fertilizer is the difference between the amount the grass requires and the amount present. I wondered how the cartogram of elements in leaves would compare to a cartogram of nutrients in the soil. For that, I looked up the Global Soil Survey data, and generated a cartogram using the median values of the elements measured in the Global Soil Survey.
This looks a bit different, and is illustrative of a couple things related to fertilizer. First, N is low in the soil, but the plant uses a lot of N. Comparing the two charts makes it clear why N is applied as fertilizer to most turfgrass sites. Second, K is relatively large in the cartogram for leaves, and much smaller in the cartogram for soil. Because the plant demand for K is relatively high, compared to the amount in the soil, K is often required as fertilizer. Third, Ca and Mg and some micronutrients are much higher in the soil than they are in the leaves, providing an illustration of why these elements are rarely required as fertilizer.
Waterfall charts provide a more explicit example of these calculations, but the cartograms are kind of fun to look at.