Is there evidence that a deeply watered lawn will develop deeper roots?

Question

Everyone says "deep and infrequent" when describing how to water a lawn, but is there evidence to back up this suggestion?

I can expound on this several ways:

1) Why would one want deep roots if one has to water so much to get water to the roots? Wouldn't a lawn with shallow roots then be easier to maintain, since not as much water is needed to get to the roots?

1a) If the answer to the above question is to develop a lawn that is drought resistant, then why is there a need to water deeply in non-drought weather? If there is water down there in droughts (otherwise, why train roots to grow deeply), certainly there would be water down there in non-droughts... and if there is already water down there... why water deeply? Wouldn't one just be forcing the water that is already deep, even deeper? Isn't that a waste of water?

2) Oak trees are very deep-rooted plants, yet the vast majority of roots are in the top 6 inches of soil... Even trees that are 100s of years old. If the roots of oak trees haven't managed to figure out that they should grow deeply in 100 years, how then can grass be expected to?

3) I am under the impression roots will grow because that's what roots do, like plants themselves. They grow and press onwards. How is starving them from water, then flooding them with water going to make them grow any better?

4) I am also under the impression that roots grow to find phosphorus, which is immobile in the soil. Wouldn't it logically follow then that roots will grow as deep as they need to in order to find the P they want?

5) Areas of the country (US) where grass grows best (naturally), have rainfall around 20-30 inches annually. Areas of the country having rainfall in excess of 50 inches annually, grass doesn't grow so well and trees dominate. 25 inches a year is 1/2 inch a week. That doesn't sound very deep to me. Additionally, many of those areas where grass grows naturally well, have drizzly weather. Areas getting 50+ inches, have monsterous storms with flooding downpours, while remaining sunny most of the time. Clearly, mothernature is not adhering to the "deep and infrequent" rule concerning her watering of the grass.

So, is there evidence to back up the "deep and infrequent" suggestion? Personally, as a human, I would like a sip every now n then rather than go all day and be force-fed a gallon of water in hopes of developing some resistance to dehydration. It doesn't seem like biology can be coaxed that way.

Update to illustrate the popularity of the "deep and infrequent" belief:

From http://www.popularmechanics.com/home/improvement/lawn-garden/the-smarter-way-to-water-your-lawn#slide-5

We have:

Too much watering can lead to fungus and a shallow root system; fewer waterings encourage the roots to grow deeper. "You want to train the roots to go down deep into the soil," he says. "I'm telling my customers if you're going to water, water every three to seven days once we hit summer. Water deeply and water infrequently."

From http://www.youtube.com/watch?v=lUubjlAuIk0

We have:

1 inch per week. Deep and infrequent.

This site http://average-rainfall-cities.findthedata.org/d/d/Kansas says kansas gets 20-35 inches annually. 1 inch per week is 50 inches. So, according to this, Kansas should be a desert? It just doesn't add up. Kansas is part of the virgin grasslands called prairies http://en.wikipedia.org/wiki/Prairie Grass grows quite well naturally in Kansas with only 20 inches per year. When rainfall increases to 50 inches in other parts of the country, we have coniferous forests develop instead of grasslands. Why is that? It isn't that grass doesn't like the water... its that the water washes away the nutrients grass needs to make proteins.

If we start in Kansas with 20-35 inches of annual rainfall and kansas having predominantly grasslands, then move east into Missouri, which has 40-45 inches of rainfall http://average-rainfall-cities.findthedata.org/d/d/Missouri we start to see more trees on the sat maps. Move farther east into KY (45-50 inches) and TN (50-55 inches), we see more trees and much less grass.

This was the principle observation of Dr. William Albrecht on the health of animals. Places that get too much rain, protein-rich things (grasses, grains) don't grow. The soil is overly weathered, which causes the soil particles to breakdown and lose cation adsorption capacity. Plus, nutrients are washed away.

William A. Albrecht (1888–1974) PhD, Chairman of the Department of Soils at the University of Missouri, was the foremost authority on the relation of soil fertility to human health and earned four degrees from the University of Illinois. As emeritus Professor of Soils at the University of Missouri he saw a direct link between soil quality, food quality and human health

http://en.wikipedia.org/wiki/William_Albrecht

According to the "foremost authority on soils", if you want grass to grow, you don't want more than 25 inches of rain annually... or less either.

Here's another one saying 1 inch of water http://www.youtube.com/watch?v=VB1wxn7H6TM

Finding someone who doesn't say 1 inch of water and "deep and infrequent" is quite a challenge.

Answer 1

I believe I have gathered enough information that an answer is now available.

Three main variables determine the direction roots grow: Gravity, light, and water. These are called gravitropism, phototropism, and hydrotropism.

Phototropism is simply that the roots grow away from the light. I wouldn't think light extends much below the surface, so this tropism is minimal to none concerning grass.

From http://en.wikipedia.org/wiki/Hydrotropism

Hydrotropism is a plant's growth response in which the direction of growth is determined by a stimulus or gradient in water concentration. A common example is a plant root growing in humid air bending toward a higher relative humidity level. This is of biological significance as it helps to increase efficiency of the plant in its ecosystem. Hydrotropism is difficult to observe in underground roots, since the roots are not readily observable, and root gravitropism is usually more influential than root hydrotropism. Water readily moves in soil and soil water content is constantly changing so any gradients in soil moisture are not stable.

Misconceptions

The greater growth of roots in moist soil zones than in dry soil zones is not usually a result of hydrotropism. Hydrotropism requires a root to bend from a drier to a wetter soil zone. Roots require water to grow so roots that happen to be in moist soil will grow and branch much more than those in dry soil.

Roots cannot sense water inside intact pipes via hydrotropism and break the pipes to obtain the water.

Roots cannot sense water several feet away via hydrotropism and grow toward it. At best hydrotropism probably operates over distances of a couple millimeters.

From http://en.wikipedia.org/wiki/Gravitropism

Abundant evidence demonstrates that roots bend in response to gravity due to a regulated movement of the plant hormone auxin known as polar auxin transport (Swarup et al., 2005).

From http://udspace.udel.edu/bitstream/handle/19716/2830/Chapter%205.%20Roots%20and%20Root%20Systems.pdf

Root growth results from cell division and the pressure developed by enlargement of newly formed cells. Cell enlargement is discussed in Chapter 11 and root growth at the cellular level is discussed by Barlow in Gregory et at. (1987). Bret-Harte and Silk (1994) question how sufficient carbon for growth reaches root meristems, which are several millimeters beyond the termination of the phloem. The older portions of roots are anchored in the soil and the tips are pushed forward through the soil by cell enlargement at rates of a few millimeters to a few centimeters daily, often following a tortuous path of least resistance through crevices and around pebbles and other obstructions. Generally, root tips tend to return to their original direction of growth after passing around obstacles, a characteristic observed in the 19th century by Darwin and others, which is known as exotropy (Wilson, 1967). Despite numerous temporary deflections, branch roots of many plants tend to grow outward for a time before turning downward (Wild, 1988, p. 121 and Fig. 5.11). The cause of this change in sensitivity of roots to gravity deserves more study.

Therefore, the roots aren't growing down because of the presence of deep water, they're growing downward because of gravity and, being a healthy root, that's what roots do. If there is some hydrotropism involved, it certainly isn't necessary since the roots are already growing in the direction of gravity.

So to get deep roots, all we need is gravity and a healthy plant.

One caveat to this may be if hydrotropism could overpower gravitropism if somehow there is more water near the surface than deeper in the soil.

From: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1838587/

The classical methods of the German botanists, also used by the Darwins included placing seeds in a hanging cylinder of wet sawdust, which resulted in roots first growing downward (gravitropism) but then growing back up toward the wet substrate (hydrotropism).

Inspection of the references reveal the roots were of "Agravitropic roots of a pea mutant". The pea was mutant in that it didn't have the capacity to respond to gravity. I've found no evidence that normal plant roots nor grass roots could do this. But even if they could, how likely is it to have a situation where the top soil is wetter than the deeper soil over a long enough period of time for the roots to respond and grow in that direction?

So for the "deep and infrequent" theory to hold water, the roots of "shallow and frequently" watered grass would be expected to grow first down, then up towards water, then after encountering light, back down again, then back up to find water, etc, etc, etc in the zig zag pattern for the life of the grass. This is, of course, assuming one could hold the water on the surface without it sinking down in or evaporating away. And it has not been demonstrated that hydrotropism can overpower gravitropism without an agravitropically mutated plant.

MSU study:

From: http://archive.lib.msu.edu/tic/mitgc/article/2001101.pdf

Common irrigation recommendations for turfgrass are to irrigate deep and infrequently in order to achieve a deep root system that will be better suited to endure prolonged drought conditions. Deep infrequent irrigation is a vague description but generally refers to applying large amounts of irrigation, 0.5 to 1.0 inch or more, in a single irrigation. Irrigating deep and infrequently is not recommended for all turf situations. Turf grown on sandy soils should be irrigated with smaller amounts of water more frequently as deep infrequent irrigations could potentially result in losses of irrigation water through leaching. Also, turf grown on fine textured soils with low infiltration rates should be irrigated with smaller amounts of water more frequently to avoid run-off and puddling on the surface.

The alternative to deep infrequent irrigation is light frequent irrigation. Light frequent irrigation would be described as applying small amounts of water, 0.10 to 0.25 inch, every day or every other day. Common perceptions of light frequent irrigations are that they promote shallow rooting in turfgrass thereby making the turf more susceptible to dry soil conditions. Furthermore, frequent irrigation applications are often implicated in increased weed interference. Despite all the negative effects put forth for light frequent irrigation applications there are some positive effects. Research by Melvin and Vargas (1996) revealed that light frequent irrigation treatments, 1/10 inch every day at 12 p.m., reduced the symptoms associated with Necrotic Ring Spot. Jiang, et al. (1998) also found that a light daily irrigation resulted in higher turfgrass quality, and reduced brown patch incidence when compared to deep infrequent irrigation based upon returning 80% of evapotranspiration weekly. Daily irrigation treatments have also been shown to have a smaller thatch layer than weekly irrigation treatments (Melvin, 1991).

In order to answer the question of deep/infrequent vs. light/frequent irrigation a research study was established at the Hancock Turfgrass Research Center in 1999 to compare the effects of the two irrigation schedules on three turfgrass species.

Materials and Methods

In 1999 irrigation and fertility treatments were initiated on Kentucky bluegrass, tall fescue, and perennial ryegrass. The three irrigation treatments were no irrigation, 1/10 inch applied daily in the early afternoon, and 0.7 inch applied weekly at one irrigation event. Fertility treatments were different amounts of urea and one treatment with com gluten meal.

Results

Results from 1999 can be found in the 70th Annual Michigan Turfgrass Conference Proceedings (Vol. 29). Trends from 1999 indicated that the daily irrigation treatments resulted in higher turf grass quality and density than the weekly irrigation and no irrigation treatments. Results from 2000 were inconclusive due to the frequent rainfall experienced in East Lansing. Research will be continued in 2001 to determine the effects of irrigation and fertility treatments on turfgrass species.

0.1 inch applied daily resulted in a better lawn than 0.7 inches applied weekly.

Other Studies

Study #1

From https://dl.sciencesocieties.org/publications/cs/abstracts/29/6/CS0290061536

Field studies were conducted to determine responses of ‘Rebel’ tall fescue and ‘Reliant’ hard fescue to deficit irrigation and irrigation frequency. Turf growing on a Satanta sandy clay loam soil (Fine loamy mixed, mesic Aridic Argiustoll) was irrigated at 50, 75, or 100% of potential evapotranspiration (ETp, i.e., turf water use when soil moisture is not limiting) on 2-, 4-, 7-, or 14-d intervals. Small weighing lysimeters adjacent to plot areas were used to obtain ETp rates. Both species performed best when irrigated every 2 or 4 d at 75 or 100% ETp.

2 to 4 days? That seems frequent to me. More so than 7 to 14 anyway.

Study #2

From http://horttech.ashspublications.org/content/16/3/466.short

'Aussie Green' and 'Celebration' produced the highest TQ rating (>7) at week 4 when watered daily. After 4 weeks of the 5-day irrigation interval, all cultivars showed unacceptable quality ratings (<7).

Based on these results, irrigating bermudagrass in 5-day intervals should be carefully monitored.

I thought bermudagrass is a weed... I can't kill it with fire, brimstone, a bottle of acid and a box of salt,,, yet the recommendation is to "carefully monitor" it with a 5-day irrigation schedule?

Study #3

From https://dl.sciencesocieties.org/publications/aj/abstracts/58/6/AJ0580060559

Dry matter yield was not markedly raised by regular nitrogen fertilization, unless irrigations were applied frequently

Food without water = no growth? Makes sense to me.

Infrequent irrigation of fertilized plots produced a lawn of only slightly reduced quality compared to that obtained when frequent irrigations were given in the absence of nitrogen

So, if we fertilize and withhold water, the lawn will look not quite as good as a lawn that is simply watered more frequently? I guess that makes sense too.

Study #4

From https://dl.sciencesocieties.org/publications/aj/abstracts/73/1/AJ0730010085

Delaying irrigation until the onset of temporary wilting, caused a significant decrease in water consumption and growth (up to 35%) in most grasses.

That makes sense... grass that is half-dead from thirst probably will use less water and grow less.

Study #5

From http://onlinelibrary.wiley.com/doi/10.1111/j.1439-037X.1995.tb00216.x/abstract

In conclusion, hard fescue had a shallower root system, shorter plant canopy, slower growth, and transpired less water to make it more drought tolerant. Tall fescue, with a deeper root system, longer plant canopy, faster growth, and greater water transpiration, is less drought tolerant at medium and severe stresses.

Hmm... So who wants deep roots anyway?

In Conclusion

5 studies + MSU + the 3 studies MSU quoted = 9 studies showing benefits of frequent watering. Frequent is a relative term, but I haven't seen any studies recommending a frequency greater than 2-4 days (most being daily). Even if I have to drag the hose around every 2-4 days, to me, that still seems pretty frequent.

I can see no reason why this issue would open for further debate. Every angle has been covered, from biology to observations in nature to real-world experimentation. I have not discovered a substantiated reason to believe one should water lawns "deep and infrequently".

Recommendations

For the best lawn appearance, don't wait until the lawn is showing drought stress, because at that point, its not the best looking lawn, obviously.

Don't water deeply. By watering deeply you're washing soil nutrients deeper into the soil. This is especially so with nitrates (NO3-), which have a minus charge and are easily leached into groundwater because the clay particles also have a minus charge and will not hold the nitrates in the soil. So by watering deeply you're wasting nitrogen and you're polluting the environment.

From https://dl.sciencesocieties.org/publications/jeq/abstracts/20/3/JEQ0200030658

Analysis of soil water from 15, 6-m continuous cores showed that as much as 95% of the NO3 applied in late August leached below the turfgrass root zone.

Maybe the reason light frequent waterings makes grass grow better is the grass gets more nitrogen, instead of it leaching beyond the rootzone.

Whatever the reason, deep and infrequent watering is the absolute worst way to water.

Credibility of university extensions:

Here we have two universities giving opposite advice:

http://www.turf.msu.edu/irrigation-practices-to-preserve-water-quality

http://www.extension.umn.edu/distribution/horticulture/DG2364.html

Lesson: Always look for studies and read the studies. Don't believe conjecture.

Answer 2

I realize this is an old discussion but I feel the need to chime in for the sake of others who find this the way I did.

It has been mentioned but not strongly enough: ornamental lawns are not natural. Comparing the growth of Kentucky Blue Grass to the patterns of grasslands and forests across a continent is ridiculous, especially from someone so insistent on empirical evidence. I can provide links to all sorts of empirical evidence about the negative health affects of smoking, the growing gulf in income inequality, and price sensitivity across different demographics, but none of that is relevant to your lawn. And neither are oak trees.

The only evidence you need is to compare regions where no irrigation is needed to maintain a healthy ornamental lawn, along with the precipitation patterns there (and taking into account typical soil conditions). Having been raised in the West where knowing how to build and maintain an in-ground PVC irrigation system is all but prerequisite to home ownership, and later living in New York (Hudson River valley) and South Carolina, I was amazed to see that almost no one in those areas have sprinklers for their lawns. Home stores don't have whole aisles dedicated to the various parts needed.

And they get DEEP, infrequent watering from nature. It can rain for two weeks without stopping. Then it can go a month without raining more than a momentary drizzle.

My neighbor waters his lawn for 5 or 10 minutes EVERY MORNING "so the soil doesn't dry out". His lawn looks like crap.

The problem is that you are interpreting "frequent" as meaning twice a week, or maybe more. What every university with an agricultural department advises is "infrequent" watering meaning once or twice per week in most interpretations. They are advising you to not water every day. But because they say infrequent and twice a week feels frequent to you, you're certain they're wrong.

What a bizarre way of looking for an argument, determined to go against the grain when it turns out you're just not very good at reading the grain.

Answer 3

Why would one want deep roots if one has to water so much to get water to the roots? Wouldn't a lawn with shallow roots then be easier to maintain, since not as much water is needed to get to the roots?

Shallow roots need more water as they have to be watered much more frequently. They also are much more susceptible to browning quicker in times of drought. Deeper roots = healthier plant with more stored up water/nutrients.

1a) If the answer to the above question is to develop a lawn that is drought resistant, then why is there a need to water deeply in non-drought weather?

To keep the roots long.

If there is water down there in droughts...certainly there would be water down there in non-droughts

The water doesn't 'stay' there in perpetuity. You still need to replenish it. It's just that more water will stay there longer, hence the less frequent need to water.

2) Oak trees are very deep-rooted plants, yet the vast majority of roots are in the top 6 inches of soil... Even trees that are 100s of years old. If the roots of oak trees haven't managed to figure out that they should grow deeply in 100 years, how then can grass be expected to?

You're comparing trees to grass. Very different organisms. But if you are curious about Oak trees, they do have very deep roots (tap roots) that do find water.

3) I am under the impression roots will grow because that's what roots do, like plants themselves. They grow and press onwards. How is starving them from water, then flooding them with water going to make them grow any better?

You're not 'starving' them. You're simply leading them in a particular direction (down, as that's where the moisture will be in an infrequent watering).

4) I am also under the impression that roots grow to find phosphorus

I can't answer that one. Someone with more knowledge hopefully can.

5) Areas of the country (US) where grass grows best (naturally), have rainfall around 20-30 inches annually. Areas of the country having rainfall in excess of 50 inches annually, grass doesn't grow so well and trees dominate. 25 inches a year is 1/2 inch a week. That doesn't sound very deep to me.

Rarely does rain fall 1/2 inch regularly each week. ;)

Keep in mind you're comparing natural moisture to artificial. For the most part, lawns are purely artificial creations.

Clearly, mothernature is not adhering to the "deep and infrequent" rule concerning her watering of the grass.

Again, if mother nature can 'drizzle' daily, grass obviously enjoys it. To do it artificially, however, wastes a great deal of water. And since shallow rooted grass is most susceptible in times of drought, you're now wasting water in a time of drought...not a great combination.

Personally, as a human

We also breath oxygen. We're very different organisms than grass. ;)

Answer 4

Others have provided good links to research so I won't repeat that but let me address your questions.

1) Why would one want deep roots if one has to water so much to get water to the roots? Wouldn't a lawn with shallow roots then be easier to maintain, since not as much water is needed to get to the roots?

You don't need to water so much. In fact you water less when you water deeply and infrequently. Water in the soil is lost in a number of ways. First evaporation. The top inch or two of the soil will dry out rather quickly. If you only water enough so 1" of soil is moist a lot of it will evaporate before the plant can absorb it which is another way soil loses moisture. Gravity also pulls the water down past where the roots can get to it. What you want is to have the root zone completely moist. Pretty soon the top of the soil will dry out but there will still be water if your roots are deep. This has the benefit of drying out shallow rooted weeds and preventing weed seeds on the surface from germinating but providing water to your deeper rooted grass.

1a) If the answer to the above question is to develop a lawn that is drought resistant, then why is there a need to water deeply in non-drought weather? If there is water down there in droughts (otherwise, why train roots to grow deeply), certainly there would be water down there in non-droughts... and if there is already water down there... why water deeply? Wouldn't one just be forcing the water that is already deep, even deeper? Isn't that a waste of water?

Your lawn needs a certain amount of total water. Let's say you determine your lawn and soil conditions need 1.25" of water every 8 days. That means a combination of rain water and supplemental water from irrigation. If it rained 1.5" that week you don't need to water your lawn. If it rained .5" you need to add .75" of supplemental water.

Water is also lost to evapotranspiration. Basically like how our body's lose water when it's hot and we sweat. That's why in the hot summer months you need to water more frequently. Some sprinkler controllers can monitor precipitation and evapotranspiration rates and make adjustments automatically.

2) Oak trees are very deep-rooted plants, yet the vast majority of roots are in the top 6 inches of soil... Even trees that are 100s of years old. If the roots of oak trees haven't managed to figure out that they should grow deeply in 100 years, how then can grass be expected to?

Apples and oranges. I think part of the difference is that grass plants are planted so close together.

3) I am under the impression roots will grow because that's what roots do, like plants themselves. They grow and press onwards. How is starving them from water, then flooding them with water going to make them grow any better? 4) I am also under the impression that roots grow to find phosphorus, which is immobile in the soil. Wouldn't it logically follow then that roots will grow as deep as they need to in order to find the P they want?

Roots grow to find water and nutrients. They don't just grow to find phosphorus though that is one of the nutrients plants uptake. Phosphorus actually helps promote root growth. A soil with sufficient phosphorus will have a lawn with larger root mass than a soil with insufficient phosphorus. The opposite would be implied by your statement "roots grow to find phosphorus".

One interesting thing regarding phosphorus. When the soil is phosphorus deficient and there is mycchorhiza (a helpful soil fungus) presesnt, the roots will attract the mycchorhiza and they will colonize onn the roots effectively increasing the root mass.

5) Areas of the country (US) where grass grows best (naturally), have rainfall around 20-30 inches annually. Areas of the country having rainfall in excess of 50 inches annually, grass doesn't grow so well and trees dominate. 25 inches a year is 1/2 inch a week. That doesn't sound very deep to me. Additionally, many of those areas where grass grows naturally well, have drizzly weather. Areas getting 50+ inches, have monsterous storms with flooding downpours, while remaining sunny most of the time. Clearly, mothernature is not adhering to the "deep and infrequent" rule concerning her watering of the grass.

I don't know which areas you're talking about but lawns need water during the growing season and they need less water when the weather is cooler such as early spring and late fall. At least cool season grasses anyway.

I think you're jumping to assumptions. It could be that areas with 50" of rainfall have more trees and less grass because the trees do better with 50" of rainfall and the trees compete for water and block sun from the grass. It's not necessarily that much water is detrimental to grass.

You also have to remember that home lawns are not very natural.

There are a lot of other reasons that you don't want your soil constantly moist. Some others are:

• Constant moist conditions promote pathogenic fungus (lawn disease.)
• Wet soil compacts more easily than dry soil. So when people and pets walk and play on the grass the soil will get compacted which causes other problems.

Many of the local university cooperative extensions have departments that focus exclusively on turfgrass. There have been numerous studies and all of them recommend deep and infrequent watering. If you search google scholar you'll find a ton.

A lot of people say you should water 1" a week but that's just a rule of thumb and not very accurate. You should water down to your root zone and only water again when your lawn shows signs of drought stress. This is how Roger Cook of This Old House recommends watering lawns and this is what I try and follow. After you determine your root depth and figure out how much water you need to cover it based on your soils composition (percolation rate) looking for signs of drought stress takes care of the environmental variables of evaporation and evapotranspiration.

Answer 5

First, you haven't said what kind of lawn you're talking about, but assuming you mean turf/sods, then they don't put down really deep roots anyway. If you want to prove that for yourself, lift out some turves from your own lawn by using a turf spade, or a half moon edger - you'll find you can get a turf up with a depth of about 2 inches, complete with roots, although that turf would need to be laid somewhere friable so that it can then root in a bit deeper. As for watering infrequently but 'deeply' that's not advice I've ever heard regarding lawns - a newly laid lawn of turves needs frequent watering for the first six weeks if the weather is dry. After that it should be fine without any at all (in temperate zones), other than dew or rain, although it's fair to say it will be in much better condition if it doesn't suffer drought, and that applies to mature lawns too. In drought, it may go completely brown, but usually recovers when rain arrives, though it may then be invaded by unwelcome guests such as moss/weeds because of being in drought previously.

Answer 6

There are thousands of professionals employed to make ball fields and golf courses look immaculate even with daily use and damage. The publications you site all cater to these people. They are concerned with the best possible outcome. Time and Cost is not a concern. And to keep turf growing at its max, you never want to over or under water it.

The lawn is (or should be) a very different place. Most of us want a lawn that can survive a two week vacation without dying. Everyday when the sun comes up that surface is going to dry out some by evaporation. If you water every day a smaller percentage of your water is going to go to the plant, a lot of it will be lost to evaporation. If you pay a water bill, you probably care about how much water is disappearing into the sky vs how much is making your lawn healthy. And because deeper soil profiles lose water much more slowly due to evaporation. And so yes deep and infrequent will train the roots to go into those deeper levels 6"-12" vs 0-3"--- if you cut your lawn longer (3.5" vs 2").

Depending on your soil texture, your soil will hold between an inch of water (sand) and just over two inches of water (clay loam) in the top foot of soil. So anything more than your capacity will pond on the surface or be lost by gravity. Water moves (downward) much faster in sand than clay,... So sand has a double disadvantage (dries quicker, stores less)

And you missed the point of the article on Hard vs Tall fescue. Tall fescue grows faster and has a higher water demand as a species not because it has longer roots. And if you are looking at a lawn species (vs professional ball field) you want one that is slower growing and takes less maintenance.

The article you sited about Nitrate movement was irrigating excessively (intentionally) they were irrigating at .8 inch per day!

And finally, several people have made similar points, but timing matters. Grass doesn't grow in the winter A) so 1" a week for a 30 week summer =30" Hotter areas need more (longer growing season and more lost to evaporation). Cooler areas need less (shorter growing season and less lost to evaporation).

So, ideally you would link your watering to your local rainfall and local evaporation, but until recently, the data wasn't available to the public. Hence the 1" a week rule: Something that is a good baseline for a large swath of the country (USA). Obviously your not going to turn on your sprinkler when its frozen!