The evapotranspiration (ET) is a useful value for turfgrass managers.

 This calculator using the Hargreaves equation to estimate ET_o is now, thanks to translation by Yukio Ueno, available in Japanese.

Knowing the ET_o and the ET_c allows one to have some idea of the probable consumptive water use of the grass.

When I don't have all the weather data for a location, but want to know the evapotranspiration (ET), I use equation 52 (the Hargreaves ET_o equation) from the FAO Crop evapotranspiration book.

I made this Shiny app so anyone can input the latitude, date, and temperature to find an estimate of ET. The code for the app is in this Github reposository.

Another inquiry:

What would you advise is the best course of action with;

1) Bicarbonates in irrigation water
2) Ca, Mg etc in water that makes the water hard??
3) How do you soften the water?

Bicarbonate is not a problem. Don't worry about it. For more, see this or this.

Hard and soft water is not how one should think about irrigation water for turfgrass. Rather, I would look at this, this, or this. The main things to check are the salt content of the water (given as the EC_w or the TDS) and the sodium adsorption ratio (SAR).

I received this inquiry last week:

"When looking at water quantity for a new golf course, you have to determine how much water is needed obviously so what I want to know is.
 
1) How do you calculate how much water is needed for a given area (the whole golf course?)
 
2)  I know you have to look at the driest year data and base it on that but I understand you have to measure how much a grass plant and soil will lose via Evapotranspiration so you know what you have to replace so what methods do you use to find this out?"

I suggest calculating a water budget for the location using the method described by Gelernter et al. with this supplement providing the details for the calculations.

I'm giving five presentations at the Northern Green Expo.

• The (New) Fundamentals of Turfgrass Nutrition
• Nutrient Use by the Grass and Nutrient Supply by the Soil
• Calculating the Fertilizer Requirement for any Turfgrass, Anywhere
• Soil Water Management: Amount, Timing, and Syringing
• Instead of Shade, Let's Talk About Light

I combined the handouts for each presentation into this single document for easy reading. I especially like this part:

That's the question Bill Kreuser asked about syringing to reduce the temperature of cool-season turf during periods of extreme heat stress.

Syringing - an essential practice or a waste of time? Thoughts? Read more here: http://t.co/rK5SfqsRag pic.twitter.com/GSrJmzofck

— Bill Kreuser (@UNLturf) July 17, 2015

He prepared this document with a nice summary of the topic. Spoiler alert: "Does syringing help? Unfortunately, the answer is most typically no."

For more about syringing and irrigation, see:

• Summertime syringing to cool bentgrass greens: I wouldn't do it today
• Irrigation management in summer: timing, amount, syringing, and water quality
• 夏の散水管理：タイミング,水量,シリンジング,および水質
• For irrigation, which is better? Deep and infrequent, or light and frequent?

My turfgrass talk column in the May-June issue of GCM China explains how to calculate the amount of irrigation water to apply when one is trying to keep the soil salinity (EC_e) from exceeding a threshold value.

The article is available in both Chinese and English.

• Download the article in Chinese
• Download the article in English

If the salt is not leached, and accumulates in the soil, the grass can die. To prevent the accumulation of salt, more water than the grass can use must be applied. This causes leaching as the extra water moves below the rootzone, carrying some salt with it.

Good drainage is essential when salt in the irrigation water requires leaching to be done. In the photo below, there is a low area below the drain, and salt accumulation in the soil at that spot prevents grass from growing.

For more on this topic, see the preceding article in this series: Do you know how much salt is in your irrigation water?

My column in the March-April issue of GCM China is about salt. The salt in water is invisible, so one needs to test the water to find out how much salt is in it.

As I wrote in the article, water with total dissolved solids (TDS) of 800 ppm would add 56 g salt/m² (11.2 pounds salt/1000 ft²) in a 2 week period if irrigation is applied at 5 mm/day. Being aware of how much salt is in the irrigation water is the first step in determining if leaching will be required.

• Download article in Chinese
• Download article in English

In my second presentation at the Ontario Golf Course Management Conference, I discussed three things about soil moisture and irrigation that may lead to improved turf conditions in summer.

More discussion below, but first the handout, and these slides.

The first thing I discussed was irrigation frequency. I explained that daily irrigation can be used to keep the soil drier, and with a higher air content, than deep and infrequent irrigation. This annotated chart explains how lower soil moisture can be the result when irrigation is supplied daily.

Then I talked about water quality, and I finished the presentation explaining how a soil moisture meter can be used to estimate the relative evapotranspiration at differing environments on a property.

I didn't include any discussion of wetting agents in the presentation, but I would have talked about this if there was more time. Data show there is no such thing as wetting agents that retain more water or move water through the soil. Understanding what wetting agents really do is important to make the best use of these products.

There is a good article by Karcher and Richardson in GCM about the effect of wetting agents. In the article, they point out something important:

It is often stated that some wetting agents move water rapidly through the root zone while other products retain considerable moisture near the surface, but the data to substantiate such claims is limited.

I have been surprised, in conversations with turfgrass managers, to learn just how prevalent that thinking is, that soil surfactants can be divided into classes that retain more water in the soil, or that act as penetrants and may reduce soil water content.

If some wetting agents really do retain more water in the soil, and other types make water move through the soil more quickly, there should be some data to show that, right? This should be such easy data to get if there really were an effect. Because there doesn't seem to be such data, it would seem that wetting agents don't really produce those diverging results.

What wetting agents do, when the soil moisture content is measured after application, is this. They increase the uniformity of soil moisture. From Karcher and Richardson:

Wetting agent products tested in this trial effectively reduced localized dry spot incidence and increased soil moisture uniformity over a wide range of depths (3 to 8 inches) compared to untreated turf.

This is same result reported by Soldat et al. in this 2010 Soil Science paper:

The uniformity of soil volumetric water content of the surfactant treatments was significantly greater, and soil water repellency was lower [and] … surfactant treatments were faster to recover from the drought … The surfactants had a minimal effect on soil water content … however the three surfactants significantly improved soil moisture uniformity compared with the untreated control in both years during drought conditions … These results indicate that the surfactants evaluated are effective tools for improving soil water content uniformity, maintaining good visual appearance, and reducing soil water repellency in sand-based golf putting greens under conditions of drought and irrigation restrictions.

The data show two things. Soil surfactant (wetting agent) applications increase the uniformity of soil moisture. Soil surfactant applications reduce localized dry spot. If there are data showing some wetting agents retain more moisture in the soil, and others make water move through the soil more rapidly, I would love to see them.