Viridescent - the Asian Turfgrass Center blog

Soil Nutrient Guidelines and Turfgrass Nutrient Requirements

When managing turfgrass, we want to make sure there are adequate nutrients available in the soil to meet the requirements of the grass, and we must be especially careful about this in sand rootzones. Why is that? Because sand rootzones are relatively low in nutrient-holding capacity. 

With this in mind, Dr. Larry Stowell from PACE Turf and I have developed the Minimum Level for Sustainable Nutrition (MLSN) guidelines for turfgrass. This is an approach to managing soil nutrient levels that can help decrease fertilizer inputs and costs, while still maintaining excellent turfgrass performance.

These guidelines are based on a review of data from 6500 turfgrass soils rated average to good by turf managers, along with some relevant research and observations to fine-tune the guidelines specifically for nitrogen, phosphorus, and potassium, the three most important elements applied as fertilizer.

These are conservative guidelines, meaning that even though the MLSN guidelines are considerably lower than previously-published guidelines for turf, we are confident that with these levels of soil nutrients, there are still ample amounts to provide what the grass needs. 

Let's take calcium as an example. The MLSN guideline is 330 ppm, meaning that if soil calcium is at 330 ppm or more, plenty of calcium will be available to meet the needs of the grass, and no calcium is required as fertilizer. I've already explained how the quantity of calcium in the soil is related to expected plant use — with 330 ppm calcium in the soil, that is approximately how much calcium the grass would use in 30 years. 

We can think about this another way. Grasses use water from the soil as water comes in through the roots, moves up through the plant, and the water is transpired through the leaves during the day as the stomata are open. Let's imagine a hypothetical turfgrass area with transpirational water loss of 1,000 mm over the course of one growing season. That is water use by the plant of 1,000 L for every square meter of turf, 1,000 L of water going into the roots over the course of a growing season. 

That same square meter of turf may produce about 400 g of clipping yield (dry weight) per year. And if we have calcium in the clippings at 0.5%, on average, that makes a total harvest of 2 grams of calcium per square meter per year. 

We have the plant using 2 grams of calcium and 1,000 L of water per year. But remember, in the soil solution, we don't have pure H₂O — there are minerals such as calcium in the water also. As that water flows to the root, and into the root, all the calcium the plant requires will be supplied by mass flow* if the soil solution maintains an average calcium concentration of just 2 ppm. 

*mass flow is the movement of nutrients through the soil to the root in the flow of water caused by plant water absorption (Stanley Barber, Soil Nutrient Bioavailability, 1995)

In one square meter of rootzone, to a depth of 10 cm, we may have 150 kg of soil, thus giving us 49.5 grams of available calcium when the calcium is at the MLSN guideline of 330 ppm. In that same square meter of rootzone, assuming soil water content is 20%, we have 20 L of water (or soil solution), and assuming the calcium concentration of the soil solution is 2 ppm, which supplies all the calcium the grass requires, then we have 40 mg of calcium in solution in that one square meter.

The 330 ppm MLSN guideline gives us 49.5 grams of calcium which is 1,237 times more than the 40 mg of calcium that is in solution and meeting all the needs of the plant.

MLSN guidelines may seem low compared to previous guidelines, but a few simple calculations and we see that these guidelines are still conservative in ensuring that plenty of nutrients are available to the grass. And these guidelines were developed based on evaluating an extensive international dataset of thousands of good performing turfgrass sites, so these are the real nutrient levels in thousands of high-quality putting greens around the world. Download your own copy of the guidelines here.

Coming in April, Turfgrass Seminars from Singapore to Beijing with Dr. John Kaminski

I'm excited to announce the Asian Turfgrass Roadshow 2012. With seminars at Singapore, Bangkok, Ho Chi Minh City, Manila, Hong Kong, and Beijing, Dr. John Kaminski and I will traverse much of East and Southeast Asia in just nine days for these turfgrass science seminars.

Dr. Kaminski is Director of the Golf Course Turfgrass Management Program at Penn State and will be speaking about control of turfgrass diseases, specifically algae and dollar spot, while also providing information about turfgrass information and educational opportunities. I'll be speaking about turfgrass research projects, and their results, in Asia.

The seminars are being presented in cooperation with the Thai GCSA, the Philippine Turfgrass Association, the South China Turf Managers Association, and north China's GreenCare Association. These seminars are also being supported by The Toro Co.

I hope you will be able to join us for one of these events in April. Download the information sheet about the seminars here.

How Much Calcium Does Turfgrass Require?

Even in soils that contain relatively low amounts of plant-available calcium, that is still enough to supply all the calcium the grass requires. Why is that? Turfgrass uses relatively small amounts of calcium, somewhere in the range of 1.5 to 5 grams of calcium per square meter per year (0.3 to 1 pound calcium per 1000 ft² per year). Sandy soils with a low cation exchange capacity have the lowest levels of plant-available calcium, but that amount is still 10, 20, sometimes 30 times more than the grass will use in an entire year.

Nitrogen, conversely, is present in the soil at about 1/100^th the concentration of calcium, yet nitrogen is used by grass in about 10 times the amount as is calcium. In fact, at any one time during the year, a typical golf course putting green contains only about 5% of the nitrogen that the grass will use during the the year. Thus, we always get a response to nitrogen fertilizer, but it would be extremely rare to see a response to added calcium.

Working with Dr. Larry Stowell from PACE Turf, the Minimum Level for Sustainable Nutrition (MLSN) guidelines have been developed to provide information about managing soil nutrient levels that can help decrease inputs and costs, while still maintaining desired turf quality and playability levels. This video describes the MLSN approach to nutrient management and discusses the specific guidelines for calcium.

Sunshine, Zoysia, and Grass Performance in Asia

There are four grasses in the image above (click on it to get a larger view). We are looking at Tifeagle and Novotek (both are Cynodon hybrids), Sea Isle Supreme (Paspalum vaginatum), and a fine-bladed zoysia, probably Zoysia pacifica. This is a test on a shaded green in Manila. The green is maintained for seashore paspalum. The seashore paspalum can handle this shade, although it has a relatively coarse leaf blade compared to the zoysia. Both types of Cynodon fail to produce an acceptable putting surface in this type of shaded condition under which both seashore paspalum and zoysia can produce a good stand of turf.

In fact, this zoysia produces a really superb putting surface, as seen at right, a photo I took on the 18^th green at Wack Wack Golf and Country Club during last week's Philippine Open. It requires very little in the way of fertilizer, few pesticides, and is able to tolerate the low sunshine levels and tree or building shade that can cause Cynodon, with its higher light requirement, to fail. Wack Wack recently underwent a renovation and the Club made a wise choice to keep the native zoysia on greens and the native carpetgrass everywhere else. There are beautiful mature trees across the property, and other grasses would not produce such fine surfaces in these low light conditions, but the zoysia and Axonopus thrive.

Many people ask me "what type of zoysia is that?" My best answer is that it is probably a type of Zoysia pacifica (previously called Zoysia tenuifolia), and I base that on a paper published in 2005 by Akamine et al. in volume 33 of the Journal of the Japanese Society of Turfgrass Science entitled "Morphological Characteristics of Zoysia tenuifolia Willd." In the research project reported in that paper, Akamine et al. found that Z. pacifica leaves are folded in the sheath, as compared to Z. matrella leaves which are rolled in the sheath. Upon close inspection, I found that the fine-bladed zoysia from the greens at Wack Wack has folded leaves, while the leaves of a typical Zoysia matrella from Japan were rolled.

For more information about sunshine, shade, turfgrass performance in Asia, and links to a lot more information about assessing the sunshine hours close to your location, here is a video I've recorded with Dr. Larry Stowell from PACE Turf about light.

Calcium for Turfgrass: is there enough in the soil?

The answer, almost certainly, is yes. These calculations of how much calcium the grass uses, compared to how much plant-available calcium is in the soil, leave little doubt that there is almost always more than enough calcium in the soil to meet the needs of the grass.

How much calcium does grass use?

Let's take a turfgrass site at which clippings are removed, and estimate how much calcium is removed, or harvested, in one year. A reasonable estimate for annual clipping yield of maintained turfgrass is about 400 g m^-2. A reasonable estimate for calcium in the dry matter of turfgrass clippings is about 4500 ppm = 4.5 g kg^-1 = 0.45%. So if we harvest, over the course of a year, 400 grams of clippings from each square meter, and if those clippings contain on average 0.45% calcium, then the mass of calcium harvested from one square meter each year is:

400 g x 0.0045 = 1.8 grams of calcium removed each year

How much calcium is in the soil?

We've just calculated that in the situation where we remove the clippings from a maintained turfgrass area, we may be removing about 1.8 grams of calcium from each square meter each year. Let's now imagine that our root system is 10 cm deep, and that the bulk density of the soil is 1.5 g cm^-3. In one square meter, then, to a depth of 10 cm, we have a volume of 100 L, and a mass of 150 kg. Let's say this is a sandy soil, with a relatively low cation exchange capacity, and that the plant-available calcium (the calcium that is in soil solution and on cation exchange sites) is at a concentration of 400 ppm = 400 mg kg^-1. How much calcium is that?

150 kg of soil x 400 mg/kg = 60,000 mg of calcium = 60 g of calcium

Three Decades

That's how long it would take, 33.3 years, to be precise, for the grass to use 60 grams of calcium if harvested at the rate of 1.8 grams of calcium per year. There is much more calcium in the soil than is required for healthy turfgrass, even in soils that have relatively low amounts of calcium.

World Cities Plotted by Climatological Normals, February

February is another good month, on average, to grow grass in Bangkok, Chennai, Colombo, and Mumbai. Why? With average temperatures more than 25°C and sunshine well above 200 hours for the month, the growth of warm-season grasses can easily be controlled by turfgrass managers through adjustments in the amount of water and nitrogen applied. 

Hainan Island is sometimes referred to as the "Hawaii" of China, but Sanya is considerably cooler and has a lot less sunshine than does Honolulu in February. For about six months of the year, Sanya is a lot more like Hilo than Honolulu, and that means slightly cooler temperatures and significantly less sunshine.