WATER Two (also)
 
Debate: Deep, infrequent irrigation is best for root growth or Light, frequent irrigation is best for root growth.
 
 

2. energy budget method
Rn = H + LEt - G


Where Rn = net radiation
H = energy going into heating the air
LEt = cooling from vaporization of water
G = soil heating
 
Factors other than evaporative demand affecting water use
 
Soil moisture
 
You can think of water use by turf as a pumping system. The water source is soil moisture, the plant is the piping system and solar radiation and water diffusion as the pump.
 
Water cannot be pumped from a dry well nor can it be pumped from a well without a power source.
 
When soil moisture is high, water uses primarily a function of evaporative demand (pump capacity) and estimates based on that demand are estimates of maximum water use.
 
As soil moisture becomes less than field capacity, water use becomes more and more function of moisture availability.
 
The plants can also interact with both evaporative demand and soil water potential to affect the transpiration stream, for example stomotal regulation (drought avoidance).
 
Many studies have shown water uses is directly related to the available soil water. Quackenbush and Phelan (1965) suggested that water savings can be made with little loss in turf quality by allowing short periods of water stress between irrigations.
 
Danielson et al. (1981) measured water use with Kentucky bluegrass. One soil was irrigated 200% of field capacity with other plots at various lesser percentages. Irrigation to 80% field capacity reduced quality only 10% while reducing consumptive use by 20%. Quality was dramatically reduced at watering levels below 70%, but rapidly recovered when watered fully.
 
In several California studies, turfgrasses were irrigated at 100, 80, and 60% of ET values estimated from a modified class A pan. Reducing water applications to 80% ET decrease quality ratings only 3% for the cool season species and 5% for the warm season species. Even at 60% of ET, bermudagrass quality was better than acceptable and not significantly different from bermudagrass at 100% of ET.
 
Available data show that carefully manage deficit irrigation is a means towards potential savings in water with relatively small losses in quality.
 
Hazards from overwatering may be of greater importance than potential quality losses from lower levels of irrigation.
 
It should be noted that all of the above experiments were conducted with minimal traffic.
 
Several other factors enter into the relationship between water supplied hand water used by grass.
 
At optimal soil moisture levels, plants retain turgor were under all but the most extreme conditions of of evaporative demand.
 

With reduced reductions in soil moisture, turgor is progressively reduced and two things happen.

1. Closing stomatal guard sells, which is a drought avoidance mechanism.
2. While this reduces water loss, it also reduces CO2 entry and therefore photosynthesis and growth.
 
Slightly reduced top growth has the effect of allowing roots to partition available photosynthates and encourages deeper rooting.
 
Deeper and more extensive rooting, if soil temperatures are not limiting, allows exploration of more stored soil moisture and because of the greater reservoir reduces a potential degree of water stress at any stage between irrigations (drought avoidance).
 
 
Mowing
 
Evaporation or transpiration increases as surface area increases.
 
Increased mowing height and amount of top growth can be expected to increase water use, since increased leaf area enhances potential transpiration losses.
 
It also changes the geometry of the plant canopy surface, making it rougher (allowing for more turbulent gas exchange between the canopy and bulk air), causing less boundary layer resistance, and increasing the capacity for absorbing advective heat.
 
A secondary effect of increased top growth is an increase in root growth. This beneficial response results in a greater water source to exploit.
 
Shearrman and Beard (1973) study water used by 'Pencross' creeping bentgrass in a growth chamber. Increasing the mowing height from 0.7 to 2.5 cm increase the water use rate by 50%. Mowing at the 12.5 cm results in an additional 37% moisture loss when compared with the 2.5 cm hieght. This same study also showed the water use could be increased by 41% when mowing frequency was increase from biweekly to 6 times per week.
 
Feldhake et al. (1983) found a 15% increase in water used by Kentucky bluegrass mowed at 5 cm compare to Kentucky bluegrass mowed at 2 cm.
 
Kim (1983, 1987) found that grasses with horizontal leaf orientations and limited leaf extension rates use less water than their opposites under suboptimal or optimal growing conditions (height and fertility).
 
Mowing frequency and mower sharpness can also affect water in use. In the 1973 Shearman and Beard study they found that water use of 'Pencross' creeping bentgrass increased by 15% as mowing frequency increased from 1 to 12 times every 14 days.
 
Immediately after mowing there are is a temporary increase in water loss from cut leaf ends that is aggravated by shredding tearing, or bruising caused by dull blades.
 
This is a transient effect, however, and only a small amount of the total water used. It is more important when mowing is frequent, such as on a green.
 
Fertilization
 
Any cultural practice that increases leaf surface area, Internode length, and vertical leaf extension rate should also increase water use.
 
Nitrogen fertilization increases shoot growth so increases in water use under high nitrogen should be expected.
 
Shearman and Beard (1973) found that preconditioning 'Pencross' creeping bentgrass with four levels of N (0, 50, 250, and 500 mg L-1) resulted in a corresponding increase in water use. Leaf width, shoot density, and shoot growth increased with increasing N levels and these morphological changes were positively correlated (r >= 0.80) with water use rates. Water use was negatively correlated (r = -0.98) with stomatal density that decreased as N increased. Excessive N levels (1500 mg of N L-1) reduce shoot density, shoot growth, and water use rates.
 
Kim (1983) examined the influence of different cultural practices on the ET rate of nine warm season grasses. When turf was maintained under optimum N fertilizer levels (1500 g are-1 growing month-1 depending on the turf species) higher ET rates were observed then when under low N conditions.
 
N fertilization of creeping bentgrass golf greens during times of heat stress can marginally reduce root growth because carbohydrate reserves, otherwise available for maintenance of roots, are diverted for increased shoot growth.
 
Drought stress may be observed under these conditions because the impaired root system cannot provide enough soil water to replace that loss to the atmosphere by transpiration.
 
Effect of Phosphorous & Potassium
 
At this time, research data are limiting concerning the influence of P and K on water requirements of turfgrasses.
 
Potassium fertilization increases drought, heat, cold, and disease resistance.
 
Potassium increases root production which, by itself, may increase the available soil water reservoir and the potential consumptive water use of turf.
 
Work at Nebraska with 'Fylking' Kentucky bluegrass, also showed that wilting decreased with increasing K levels (Shearman 1982).
 
Schmidt and Breuninger (1981) found K applications aided in the recovery of drought stressed Kentucky bluegrass.
 
Christians et al. (1981) showed that the response of Kentucky bluegrass to K was dependent upon the other nutrients applied. For example, when high K 10.8 kg are-1) was applied with high N or P applications turfgrass quality was reduced. High K levels in combination with low N or P levels improved turfgrass quality.
 
P has also been shown to influence the leaf water potential at which stomates close by apparently increasing sensitivity of the guard cells to abscisic acid.
 
Soil compaction
 
Typically observable effects of compaction on turfgrass growth are reductions in both shoot and root growth.
 
In a study by O'Neil and Carrow (1983) 'Derby' perennial ryegrass was grown under three compaction levels. It had an average daily water use of 1.01, 0.63 and 0.32 cm during the last 20 days of the experiment with no compaction, moderate compaction, and heavy compaction.
 
There was no significant difference in water use efficiency (g of tissue g of water-1) because of the reduced growth associate with compaction.
 
With 'Pennfine' perennial ryegrass, Sills and Carrow (1983) found a 28% reduction in water use in compacted soil associate with a 30% reduction in clipping yield.
 
Typically watering practices by turf managers on compacted areas involved frequent light waterings to compensate for low infiltration rates and shallow roots. With reduced top growth this means increased runoff potential and evaporation loss from soil surfaces that may more than compensate for reduce water used by the grass and may mean a net increase in irrigation under actual field conditions.
 
Plant growth regulators (PGR)
 
Reduction of cell elongation is typical of growth regulators such as mefluidide.
 
However, the influence of these PGR's and others on the water requirements of turf is not conclusive at this time.
 
Johns and Beard (1982) reduced the growth of St. Augustinegrass and bermudagrass with flurprimidol. Consumptive water use was reduced by up to 29% when compared to untreated checks. A significant reduction in leaf area index was also found.
 
In another study (Borden and Campbell, 1985), the water requirement of paclobutrizol and MON-4621 treated zoysiagrass was reduced 22%. Decrease growth was also observed
 
Doyle and Shearman (1985) tested the effects of growth regulators on Kentucky bluegrass turf. Evapotranspiration was initially lowered by the chemicals tested, but amidichlor, flurprimidol, and mefluidide-treated turf exhibited increased ET rates 35 to 42 days after treatment because of enhanced turfgrass growth following the suppression period..
 
The short-term effect of reduced turfgrass shoot growth due to PGR applications appears to be reduction in water use.
 

However, the long-term water use rate may not be any lower (or may actually be higher) if:

1. An extended increase in shoot growth occurs following secession of treatment;
2. N applications are made to the turf to mask phytotoxic effects of the PGR;
3. The plant becomes more susceptible to environmental stress to direct or indirect effects of the PGR
4. A reduction in root growth due to decrease shoot growth results in a need for more frequent irrigation to prevent drought stress.
 
Abscisic acid
 
Abscisic acid (ABA) prevents stomatal opening and promotes stomatal closure.
 
Kim (1987) demonstrated 4.0, 7.6, and 1.6-fold increases in endogenous ABA levels in bahiagrass, bermudagrass and St. Augustinegrass, respectively, following 13 days of drought. Evapotranspiration rates have been shown to be low for bahiagrass, medium-low for bermudagrass, and high for St. Augustinegrass.
 
ABA reduced transpiration rates in a Texas study of Pencross creeping bentgrass and Tifway bermudagrass by 59 and 12%, respectively
 
Libscomb and Welterlen (1986) and Rose et al. (1986) found no transpiration reduction from cool- or -warm season turfgrass sods treated with ABA.
 
Leaf age, N and P nutrition, kinetin levels and previous exposure to water stress have all been found to influence the stomatal response the ABA.
 
Anti-transpirants
 

Anti-transpirants work in several ways:

1. Chemicals such as hexaoctadecanol, cetyl-alcohol and steryl-alcohol reduce transpiration by forming a mono-molecular layer located at the water-air interface in the leave mesophyll which reduces transpiration loss of water:
2. The metabolic inhibitors phenylmercuric acetate (PMA)and dodecenylsuccinic acid (DSA) prevent stomatal opening.
3. Wax and oil emulsions prevent water loss by completely covering the leaf surface with a film.
 
Roberts and Lage (1965) increased the growth (dry weight) of Kentucky bluegrass by addition of cetyl-stearyl-octadecanol toe applied nutrient solutions. These alcohol compounds, however, are too costly to apply to large areas of turf, making their commercial use unlikely.
 
Phenylmercuric acetate and DSA have some promise as turfgrass anti-transpirants. Davenport (1966, 1967) found PMA and DSA to be effective in reducing transpiration waters from creeping red fescue and colonial bentgrass.
 
At Texas A&M, a mixture of DSA and Aqua-Gro reduce the water requirements of Penncross creeping bentgrass by 30% without visual injury (Stahnke, 1981).
 
Stomatal characteristics
 
Kim (1987) presented a major examination of the characteristics of 11 major warm season turfgrasses. Stomata of bermudagrass were sunken, wax protected, and closed rapidly following the onset of drought stress.
 

All grasses had low ET rates under both drought stress and non-drought stress conditions.

A high degree of wax accumulation was associated with low ET rates of buffalograss and zoysiagrass.

Bahiagrass had high ET rates under nonstress conditions but very low ET rates once stressed. This was attributed to rapid stomatatal closure.

 
This stomates of centipedegrass and St. Augustinegrass were not protected by wax and reopened during drought stress.
 
This was also confirmed by Peacock and Dudeck (1984) for St. Augustinegrass. These two grasses have high ET rates under both drought stress and in non-drought stress conditions..
 
These factors make the use of my growth regulating compounds more feasible in terms of reducing turfgrass water use then do chemicals that would simply block or close stomates. This is true so long as these chemicals do not decrease shoot density or cause a flush of posttreatment growth.
 
Species and Cultivars
 
Where direct comparisons have been made, cool-season (C3) grasses have used more water than warm-season (C4) grasses, in most cases by significant margin.
 
To date, results from water use comparisons of cultivars has not been as promising as breeders would prefer, but the premise that improve cultivars exhibiting the capacity for improved drought avoidance or tolerance can be developed
 
 Texas studies have shown that leaf orientation and leaf extension rates are important.
 
However, other studies such is that by Dernoeden and Butler (1979), with Kentucky bluegrass, have been unable to specify the criteria to be used.
 
 
 
 
 
Methods for measuring water use
 
 
For all practical purposes only soil core/probe, gypsum block, tensiometer, and TDR are used by turf managers for determining soil moisture status.
 
Managing water relationships in turf
 
What is in wilt? the visible drooping, rolling, or folding of turfgrass leaves resulting from a loss of turgidity.
 
Wilt occurs when the transpiration rate exceeds the uptake of water. This can happen in both dry or wet soils.
 
In wet soils it is called "wet wilt". Mostly due to dysfunctional roots.
 
Physiological drought - wilt due two internal high concentration of salts or other solutes.
 
What happens to plants when they undergo drought stress?

1. Increased rooting
2. Increased root/shoot ratio
3. decreased tillering
4. decreased leaf number and elongation
5. decreased leaf size and area
6. thicker cuticle
7. thicker cell walls
8. less intercellular space

Items 6-8 mean plant is more water efficient

Relative drought resistance of turfgrasses

1) grasses with low ET tend to be more drought resistant

2) Rooting depth is very important in drought resistance (provides avoidance)

Wilt prevention

What factors are important in wilt prevention?

Deep, extensive root system
Low ET rates
adequate soil moisture

Cultural practices to encourage deep rooting

1) Good soil aeration - reduce compaction
2) Higher cutting heights
3) Proper N and K fertility

K responses on wear tolerance and wilt prevention at rates as high as 8 lbs K/M/Yr, even on soils testing sufficient for K. Shearman at UNL recommends 1:1 ration of N:K.

4) Thatch control
 

Syringing
Important tool to control the amount of water applied to turf.
 
 

Benefits:

Relieves drought stress which can result in bentgrass death under well-watered conditions.
Applies a minimum amount of water. Important for soils that have poor infiltration rates or have otherwise been comprised.
Permits problem areas to be irrigated while well-watered areas do not become water-logged.

Negative benefits of syringed turf.
 
Submersion Tolerance of turfgrasses
 

 

Usually results from flooding which also brings soil deposits.

Soil deposits should be removed, if possible. Usually only possible on greens and other close-cut turf.
On fairway or higher cut turf, remove or plow under.

What is the problem with soil deposits? Ans: creates layers!

Submersion injury.
Submerged turf quickly becomes anaerobic within several hours. Root hairs die and root growth stops.
Water and Nutrient uptake stop. This is why submerged turf often becomes chlorotic, no nitrogen uptake.

Injury determined by

1. turf species
2. duration of submergence
3. depth of submergence -leaf tips showing; very important '0'
4. physiological condition of the plant tissue
5. temperature
6. light intensity
 
Scald
 
When turfgrass plant collapses and turned brown under standing water, high temperatures, and intense light.
 
Scald injury is more severe at higher humidities.
 
Succulent, rapidly growing tissue are more susceptible scald.
 
No data are available on the relative scald tolerance appears turfgrass species and cultivars.
 
The only real management tool is adequate drainage.