Nutrients, calcium, potassium, and Park Grass at Eastern PA Turfgrass Conference, January 2014
This information supplements the presentations made on these topics by Micah Woods at the Eastern Pennsylvania Turfgrass Conference and Trade Show on 7 and 8 January 2014.
For general information about turfgrass management, see the Asian Turfgrass Center website. Follow Micah Woods on Twitter @asianturfgrass for turfgrass photos, links to interesting articles, and new information about turf management.
Minimum Nutrient Requirements for Putting Green Turf
Some turf nutrition classes or seminars focus on the role of individual elements. Each element is important, but if it is present in adequate amounts, then it really doesn’t matter what the function of that element is. Turfgrass managers must answer two important questions about each essential element:
- Is this element present in adequate amounts?
- If the answer to the first question is no, then how much of this element must be supplied to meet the grass requirements?
The approach described in this presentation utilizes the minimum levels for sustainable nutrition (MLSN) soil nutrient guidelines. These guidelines were developed as a joint project of PACE Turf and the Asian Turfgrass Center. For a full explanation of the development and practical application of these guidelines, see Just what the grass requires: using minimum levels for sustainable nutrition from the January 2014 issue of Golf Course Management.
We can use a four step process to determine the nutrient requirements for a particular site. This process involves estimating how much of an element the grass will use, and then determining how much can be supplied by the soil, and how much must be applied as fertilizer.
1. The elemental content of fertilized turfgrass leaves is relatively constant
For creeping bentgrass and annual bluegrass (Poa annua), the macronutrients and secondary nutrients will tend to be present in these amounts.
| Element | Percent in leaf dry matter (%) |
|---|---|
| Nitrogen | 4 |
| Potassium | 2 |
| Phosphorus | 0.5 |
| Calcium | 0.45 |
| Magnesium | 0.2 |
This gives us a nitrogen to phosphorus to potassium ratio of 8:1:4.
2. The amount of nitrogen supplied to the grass controls growth and uptake of the other nutrients
Adding more nitrogen makes the grass grow more. As more nitrogen is applied, the grass use of other elements will increase.
``N supply was the primary determinant of turfgrass growth rate, plant nutrient demand, and nutrient uptake. Nitrogen uptake accounted for over 88% of uptake of all other nutrients. Uptake of P and K were strongly related to tissue N content irrespective of soil test levels."
3. A temperature-based growth potential can predict how much nitrogen the grass will use
Grass won’t grow when it is too hot or too cold. Growth potential is a function of temperature, and the temperature-based growth potential was developed by PACE Turf to produce a number from 0 to 1 (or from 0 to 100%), indicating how close the temperature is to the optimum photosynthetic temperature. Because the leaves will have a relatively consistent nitrogen and nutrient content, the growth potential can be used to estimate grass use of nitrogen and the other essential elements.
Article from 2005 Golf Course Management explaining growth potential
This is the growth potential equation:
$$ \begin{aligned} GP = e^{-0.5(\frac{t-t_o}{var})^2} \end{aligned} $$
where,
GP = growth potential, on a scale of 0 to 1
e = 2.71828, the base of the natural logarithm
t = actual temperature
to = optimum temperature
var = adjusts the change in GP as temperature moves away from to
That looks a bit complicated, but it is easily calculated in a spreadsheet. PACE Turf have prepared just that, in the climate appraisal form of their PACE IPM planning tools.
I’ve written about growth potential, the most detailed version being Using temperature to predict turfgrass growth potential (GP) and to estimate turfgrass nitrogen use.
I also wrote an article about this for the Spanish Greenkeepers Association. This article was published in Spanish: Predecir los requerimientos nutricionales y el crecimiento del cesped.
4. The MLSN guidelines ensure that soil nutrient levels remain high enough to produce excellent turf conditions
The MLSN guidelines ensure that soil nutrient levels remain high enough to produce excellent turfgrass conditions. Simply make sure that the the selected element is at or above the MLSN guideline, and you can have a high confidence that there will be enough of that element availble to the grass to produce high performance turfgrass.
MLSN article from January 2014 GCM
MLSN project page and current guidelines
Through some simple mass balance calculations, we can determine how much fertilizer, on an element by element basis, is required. This is done by estimating the harvest of clippings, which contain nutrients, measuring how much of an element is present in the soil, and determining if the element will remain at or above the MLSN guideline with that estimated nutrient harvest through grass clippings.
Long-Term Management of Lawns to Reduce Weeds: Lessons from the Park Grass Experiment
The Park Grass experiment at Rothamsted is the oldest experiment on permanent grassland in the world. Frank Rossi and I wrote an article about this experiment and its application to turfgrass management: The Park Grass Experiment and the Fight Against Dogma.
For a link to an experiment description and links to many other articles and data about this experiment, see the electronic Rothamsted Archive Park Grass page.
From the very start of the experiment, in 1856, it was apparent that the fertilizers (called manure in language of the time) applied caused different plant species to grow.
``Perhaps the most remarkable and interesting of the effects of the different descriptions of manure, upon the complex herbage of which the experimental meadow was composed, was the very varying degree in which they respectively developed the different kinds of plants … In fact, the plots had each so distinctive a character in regard to the prevalence of different plants, that the expirimental ground looked almost as much as if it were devoted to trials with different seeds as with different manures."
Lawes & Gilbert, 1859. Description of plants developed by different manures. Journal of the Royal Agricultural Society of England.
Recognizing that the plants and soils of England are different than this region, and also that lawns are mown frequently, while the Park Grass experiment is mown twice annually (treated as hay), the results at Park Grass are such that we can draw some general conclusions:
Addition of nitrogen will generally favor grasses over broadleaf weeds and will reduce the number of species present.
Withholding potassium will allow most grasses to grow and if the soil potassium gets low enough, dandelion will not grow.
Addition of nitrogen only will favor grasses, while addition of complete fertilizers will allow more species to grow.
Acidifying the soil will reduce the number of species present and will also tend to favor grasses; adding lime will increase the number of species present.
For more about potassium and dandelion, see the paper of Tilman et al..
``for soils with low potassium levels, the use of potassium-free lawn fertilizer is predicted to decrease Taraxacum because of competition from grasses like Festuca rubra."
How Much Calcium and Potassium are Required as Fertilizer?
Utilizing the approach outlined in the presentation on putting green nutrient requirements, one can estimate how much potassium and calcium the grass can use. By measuring how much of each element can be provided by the soil, it is possible to determine how much must be applied as fertilizer. For examples, see:
Calcium
- How much calcium does turfgrass require?
- Calcium for Turfgrass: is there enough in the soil?
- Calcium deficiency in turfgrass, an imaginary problem?
- A new look at calculating calcium requirements
- Waterfall chart of putting green calcium levels
Potassium
- How much potassium does grass require?
- How much potassium does turfgrass need?
- Potassium for turfgrass: interview with Larry Stowell of PACE Turf
- Using waterfall charts to look at soil nutrient levels: potassium as an example
- Making use of nutrients in the soil
Additional info
For even more on these topic, see posts on the ATC website tagged fertilizer.
In this video from the Australian Turfgrass Conference, I talked about turfgrass nutrient requirements and the role of nitrogen.
This GCSAA webcast on Putting Green Nutrient Use & Requirements is available to watch on-demand.
An excellent introduction to the relative importance of soil physical, chemical, and biological conditions, along with an introduction to this topic, is given in a video by Dr. Doug Soldat from the University of Wisconsin Department of Soil Science. His GCSAA webcast on Managing Soil to Maximize Plant Health provides practical information while putting these various aspects of soil management into context.