After 28 days, grow-in and salinity differences


I've been growing grasses in a plastic house with a lot of help from colleagues at the Thailand Institute of Scientific and Technological Research (TISTR). The idea was to see how these grasses grow in after being planted as stolons, and to see what happens when salt is added in the irrigation water. I'll be discussing this experiment at the field day in Chonburi next week.

The picture above shows the grasses that receive the irrigation with 330 ppm total dissolved solids (TDS), 28 days after planting. The seashore paspalum looks the best, and the nuwan noi manilagrass has grown-in almost as fast. The hosoba korai, which is a beautiful grass once established, still hasn't covered much of the pot.

Another thing I've found interesting is measurements of salinity in the soil with the new TDR-350. All the pots are supplied with the same quantity of water. But different sets of pots get different amounts of salt in the water.


The soil salinity in these pots is changing depending on which irrigation water is applied. That's just as expected.

For more about the TDR-350, see this webinar.


High expectations


I've rarely been so excited to read an article. Last week when I saw Energy use and greenhouse gas emissions from turf management of two Swedish golf courses, by Tidåker et al., I immediately dropped what I was doing and read it.

If you've talked with me about turfgrass management sometime in the past 18 months, our conversation may have touched on differences in energy use, and the difference in carbon emissions, caused by differences in grass selection and maintenance practices. In fact, this is one of the topics Dave Wilber and I discussed as part of our wide-ranging conversation during episode 14 of the Turfgrass Zealot Project. I don't know how to make these calculations yet, but finally with this article I've read something that provides the calculations, and that I can study so I can figure out how to do this myself.

Gelernter et al. wrote in 2014 about quantifying sustainability on golf courses. We suggested measuring and tracking the annual:

  • quantity of fertilizers applied
  • quantity and toxicity of pesticides applied
  • quantity of water used
  • fuel volume
  • labor hours
  • electricity used

One can keep track of those quantities, together with the associated costs, and from that one can check the efficiency of the operation. These quantities also serve as some of the basic data requirements for the GEO OnCourse program.

But the quantities we wrote about in the GCM article are all different: kg of N, kg of fungicide, L of water, L of diesel, kWh of electricity. By expressing all the turf maintenance activities in units of greenhouse gas emissions (expressed as CO2 equivalents) or energy use, one then has a single number for the entire course, or for an area of the course, or per square meter, that can be used to compare to other courses next door or around the world. And the use extends well beyond comparisons to other golf courses; one can use these units to compare the maintenance of a golf course to anything that has greenhouse gas emissions or energy use.

I had high expectations for the article, and I wasn't disappointed. The authors described the fertilizer rates, topdressing rates, water use, mowing frequencies, and much more, for the two courses, and then expressed those units in GHG or energy use. N rates were up to 22 g/m2, as were K rates (I think the rates for golf course turf in Sweden should usually be less than reported in the article -- using precision fertilization, or temperature-based growth potential and MLSN, will lead to lower recommended amounts of fertilizer). Sand topdressing on greens was about 10 mm/year. Irrigation of greens was about 300 mm/year. Mowing of fairways was about 85 times/year, and greens were mown about 180 times/year.


I think this is fascinating because one can consider Sweden to have relatively low inputs. If you're familiar with golf course maintenance in a tropical environment, let's say in Phuket, you might expect fairways to be mown more than 150 times a year, greens more than 300 times, about double the fertilizer, and more than twice the water use. Now imagine what happens when comparing irrigated vs non-irrigated rough? Seashore paspalum wall-to-wall vs. manilagrass? A 60 ha sandcapped golf courses vs. one with drainage and 2 cm of sand topdressing? Overseeded vs. not? The differences in energy use and greenhouse gas emissions will be huge.

What did Tidåker et al. find in their analysis? The entire paper is worth a careful study, but in summary they found mowing was the most energy-consuming activity, and mowing together with the production and application of fertilizers (especially N) contributed the most to greenhouse gas emissions. They suggest:

Appropriate measures for reducing energy use and carbon footprint from lawn management are thus: i) reduced mowing frequency when applicable, ii) investment in electrified machinery, iii) lowering the mineral N fertiliser rate (especially on fairways) and iv) reducing the amount and transport of sand for dressing. Lowering the mineral fertiliser rate is of particular importance, since GHG emissions originate from both the manufacturing phase and from N turnover after application.

Jason Haines has some interesting reads about how turf condition can be improved while at the same time reducing inputs:

More on the daily soil water balance


How much irrigation is required at a particular location? That is an interesting question, and one gets widely different answers depending on the method used for calculation.

The standard method involves taking the consumptive water use and subtracting the effective rainfall. That seems like it would be an effective way to calculate how much irrigation is required. However, that method doesn't explicitly consider the depth of the rootzone. Because managed turfgrass has a relatively shallow rootzone caused by low mowing heights, I think it makes more sense when making the calculations for turfgrass to find the irrigation requirement by using a daily soil water balance.

For a little background on this, see:

Last week I made calculations of the daily soil water balance and from that calculated the irrigation water requirement.

As an example, this is the volumetric water content (VWC) of a 15 cm deep rootzone at Fukuoka this year, assuming irrigation was supplied when the soil would drop below a VWC of 10%, and that the quantity of irrigation supplied at each irrigation event was enough to fill the soil to field capacity.


To get the quantity of water required for irrigation, one adds up the water required for each of the irrigation events. By using the weather data for a particular location, and by adjusting the rootzone depth and field capacity and irrigation rules for that location, the daily soil water balance gives a value for the irrigation requirement that should be close to the real one. By irrigation rules, I mean how much water is applied at each irrigation event, and what the threshold VWC is for applying irrigation.

For example, I calculated this for a 15 cm rootzone at Sapporo for the months of July, August, and September, using weather data for the past 10 years.


When I calculate the daily soil water balance and then add up the amount of water required as irrigation for a 15 cm rootzone depth with the rules as shown on the chart, only 2 of the 30 months on the chart had an irrigation requirement of zero. Those are September 2015 and September 2016. The month with the highest irrigation requirement was August of 2008, with 82.7 mm; July 2007 had an 82.3 mm irrigation requirement. The median irrigation requirement for those summer months at Sapporo for the past 10 years was 42.5 mm/month.

After I shared some charts of the VWC calculated from a soil water balance, @turfstuf asked me about showing the annual quantity of plant water use together with the quantity of water required as irrigation. Those charts look like this for Sapporo, Fukuoka, and Naha:




It rains a lot in Japan, so for a normal year, a large amount of the plant water requirement can be supplied by rainfall. That's why the irrigation requirement and the plant water requirement lines are separated. The gap between the lines represents the amount of water that is supplied by effective precipitation.

The rootzone depth and the irrigation rules will also have an effect on the quantity of irrigation water required. The previous charts were for a 15 cm rootzone depth. This shows the difference between a 10 and 20 cm rootzone Fukuoka for the past 10 years.


What about locations with less rainfall? Have a look at this chart with data from Stovepipe Wells in Death Valley, where it doesn't rain much, and you'll see the irrigation requirement by the daily soil water balance method is almost the same as the plant water requirement.

Stovepipe wells

Gelernter et al. used a daily soil water balance in their analysis of water use on golf courses in the United States. This approach has many applications. For example, one can predict an irrigation requirement given past weather data. One can also compare the actual irrigation amount to the predicted amount. And one can adjust irrigation rules and other parameters in the daily soil water balance calculations to find what the change in irrigation requirement would be if those adjustments were made.

Daily versus monthly calculations of ET and irrigation requirement

I showed how weather data can be used to calculate a daily soil water balance. One can adjust the rootzone characteristics, and the timing and amount of irrigation, so that the calculations are representative of what one wants to know.

By keeping track of what the soil water content would be on each day, given the actual weather conditions, and given the water holding capacity of the specified rootzone, one can find how much irrigation water would be required.

I've also made calculations using the standard method, which takes the evapotranspiration (ET) and subtracts the effective rainfall. I've used this method before to make calculations, and it made sense to me, but I've realized that this method doesn't account for rootzone depth. For turfgrass, one should probably adjust the effective rainfall calculation for each site based on the rootzone depth.

I wondered if these methods give a similar result in predicting the irrigation requirement. I had daily data from Sapporo from 2013 to 2015, and I also got the monthly averages or totals for the same time period. I've just made some calculations to find out.


I looked at the months from April to October in each year. That's a total of 21 months.

For the ET, the result is almost the same whether it is calculated daily, and summed for a month, or whether one calculates ET using the monthly data.


For the irrigation requirement, there is not a consistent agreement. I made these calculations based on an approximation of a loam soil with a 10 cm rootzone depth, a field capacity of 40% (by volume), with irrigation supplied to return the soil to field capacity when soil water content would drop below 20%.


I've got some more calculations to make about this. The standard method seemed pretty good to me until I started making the daily calculations.

The daily soil water balance at Sapporo from 2013 to 2016

One can calculate a water budget for a particular location to get an estimate of how much irrigation water is required. This article from the Green Section Record describes those calculations.

If one considers the depth of the rootzone, and then steps day by day through the year, the irrigation water requirement can be calculated as part of the daily soil water balance.


I downloaded data for Sapporo for the past few years. Since the ground is covered in snow during the winter, I'll just show the daily water balance from 1 April to 31 October. This is for a simulated 10 cm rootzone with a field capacity of 23% and irrigation applied to keep the soil from dropping below 10%. That will be something like a golf course putting green. The blue line shows the soil water content. The black circles show the irrigation events. Interesting stuff.





Two fine articles about two important topics

When I visit Japan, I like to try the various flavors of soft ice cream as I go to different places. This is peanut soft cream in Chiba prefecture.


Another thing I like to do is browse the magazines to find interesting articles. I had a chance to see recent issues of Monthly Golf Management this week, and I was pleased to see two articles that I recommend in English are now available in Japanese.


If you are in Japan, read them in the magazines. For the original versions, if you haven't read them yet:

How to develop a water budget for your golf course: "How much water does your golf facility need each year to keep the turf healthy?"

Turfgrass fertilization: "supplemental nutrition is typically necessary to strengthen critical plant components so turf can provide desirable playing surfaces ... This article covers several aspects of turfgrass nutrition, such as determining how much fertilizer is actually needed, fertilizing for enhanced playability, the economics of turfgrass fertilization, and dispelling some of the myths surrounding fertilizer applications."


Water quality and pesticide performance

This is a useful reference from Purdue Extension on water that goes into the spray tank. From the guide:

"Water often comprises ninety-five percent (or more) of the spray solution. What affect might it have on product performance? Research clearly shows that the quality of water used for spraying can affect how pesticides perform. Its effect on product efficacy is reflected in the success of your spray operation ...

Time spent addressing the quality of water used in the spray tank can pay big dividends. This publication provides an overview of water quality and related factors known to affect pesticide performance; testing methods and options to improve the quality of the water used are discussed."


I learned of this document when I read Megan Kennelly's post on nozzles and water quality.