Understanding Turfgrass Nutrient Requirements
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Calcium deficiency in turfgrass, an imaginary problem?

Short_cutt-1The inimitable Dr. Frank Rossi from Cornell University spoke about supplemental calcium for turfgrass in the 28 May 2012 ShortCUTT podcast, saying it is time to stop worrying about "imaginary problems." So is a shortage of calcium really an imaginary problem? Basically, yes.

The new MLSN soil nutrient guidelines, a joint project of PACE Turf and the Asian Turfgrass Center, include a soil calcium level of 331 ppm (Mehlich 3 extractant) as a guideline – if the soil has less than 331 ppm calcium, add enough to increase the soil to that level.

But in almost all turfgrass soils, even in the low cation exchange capacity sands used for many golf course putting greens or sports fields, the soil calcium will be more than 331 ppm. Using the MLSN guidelines, we can say that calcium is not required as fertilizer in that situation in order to produce high quality turfgrass. Let's make a few calculations to show why.

Actively growing putting green turf may produce on average about 100 g of dry matter per square meter harvested as clippings each month. 

If the dried clippings contain 0.5% calcium, a more than sufficient amount, that is a monthly harvest of 0.5 g calcium per square meter per month. That is what the grass is using. And that is how much calcium the soil must supply.

Calcium, of course, is primarily supplied to the roots by mass flow, moving to the roots with water, dissolved in the soil solution. The water use of the grass can be estimated by evapotranspiration (ET). The ET varies with grass type and weather conditions, but let's assume the ET averages 5 mm per day. That is equivalent to 5 L of water used per day per square meter of turf. 

With 5 L of water per day, and 30 days in a month, we have 150 L of water used per month, and that water needs to contain at least 0.5 g of calcium to supply what is harvested through clipping removal. What is that concentration then, in soil solution? It is 0.5 g / 150 L = 500 mg / 150 L = 3.3 ppm. What is the typical range of calcium concentration in soil solutions? About 40 to 400 ppm. So there is typically a much higher (by a factor of about 10) level of calcium in soil solution than the grass requires. 

That is why Dr. Rossi can call calcium deficiencies or perceived shortages of calcium an imaginary problem.

For more about calcium and turfgrass see these links:

Understanding Turfgrass Nutrient Requirements

A New Look at Calculating Calcium Requirements

Calcium for Turfgrass: is there enough in the soil?

How Much Calcium Does Turfgrass Require? with video

And here is a recent video that poses the question, is supplemental calcium necessary?

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