I've been doing some research about turfgrass nutrient uptake in 2 dimensions at the soil surface (grams of an element harvested per square meter) and how that is related to soil nutrient depletion in 3 dimensions in the soil volume (grams of an element removed from the soil per unit of soil volume). As so often happens in these type of researches, I'm delighted to find that Wayne Kussow already studied this.
The amount of nitrogen supplied to the grass controls how much biomass will be produced. That amount of biomass then determines the amount of other elements that will be used. Kussow et al. summarized this phenomenon in their Evidence, Regulation, and Consequences of Nitrogen-Driven Nutrient Demand by Turfgrass.
In a paper I hadn't seen before, from 1995 in the Wisconsin Soils Report (for more from this excellent column, see here, and here), Kussow wrote about manipulating creeping bentgrass nutrition. What did he find?
By going from 2.0 to 8.0 Ib N/M/season [10 to 40 g N/m2/year], there was a substantial increase in shoot growth. This, in tum, altered the nutrient demand of the turfgrass and clipping concentrations of several nutrients changed accordingly. Without this change in nutrient demand, uptake of nutrients such as P and K remained unchanged even when the nutrients were applied.
And then this choice quote:
How many more times do I have to say that applying nutrients to turfgrass growing on soil already well supplied with the nutrients is a waste of time and money?
I'm studying this, of course, as part of further development and research related to turfgrass nutrient requirements and the MLSN guidelines. One of the innovative approaches we have taken with the MLSN guidelines is to relate the 2-dimensional harvest of nutrients to the 3-dimensial stock of nutrients in the soil. Then we account for that relationship in the resultant fertilizer recommendations. For an example of this, see the mlsn_K calculator to determine K requirement.
With the MLSN guidelines, we can optimize turfgrass performance without wasting time or money.