4 Irrigation management and optimisation for a football pitch located in South East London

Irrigation management and optimisation for a football pitch located in South East London

By P.M. Sharples

Reaseheath College, Nantwich, Cheshire. CW5 6DF

ABSTRACT

In the United Kingdom, infact Worldwide, there is a relatively small amount of data available for research into irrigation scheduling and crop coefficients (Kc) for sports turf surfaces. Crop coefficients (the ratio between ETo and ETc) allow correct application rates for irrigation to be calculated. This paper is written with the purpose of investigating the current literature available to determine crop coefficient values, for use with first class football pitches, cut at a height between 25 and 38mm, based in South East London, and to report upon the potential managerial, soil and climatic scenarios affecting this.

The main focus is to establish the effects that the key management practices i.e. mowing, aeration, and fertilisation could have on turfgrass water consumption and utilisation. To research their likely effects upon crop coefficient values and examine the role of the climate and atmosphere. Only estimations for Kc values were obtained, the value of these toward any scheduling and planning irrigation applications is highly questionable.

In the absence of accurate, calculated predictions for sports turf water use rates in the South East of London and the lack of time to formulate any predictive research, the models for Kc values investigated by Arizona State University were applied. The investigated and reviewed effects of management and micro-climate were draw upon and incorporated into suggested Kc values. Although with several years of weather data, and importantly, turfgrass water use rates, accurate crop coefficients could be developed and calculated.

The best approach toward irrigation scheduling will be to be aware that all models currently used for estimating crop and atmospheric water use have their limitations. It is advisable to combine the numerous methods available in order to determine soil water, weather, and plant conditions before application of water.

INTRODUCTION

Water, there is only so much of it and nature is not making new supplies, only recycling a portion of it. In fact, much of the world's water supply - in excess of 99% - is unavailable for man's most important uses - drinking, manufacturing, sanitation, recreation and irrigation - because it is tied up in the world's oceans and polar ice caps. The amount of water on the earth is essentially non-destructible and fixed. World wide, some 80,000 to 85,000 cubic miles of water evaporate from the oceans each year.

It is thought that many in the turfgrass related industries are guilty of misusing water. The consequences of not applying what is now known and available in these areas is that we are borrowing a major source of water from the future and missing an opportunity to become leaders with water conservation.

This paper is concerned with the data gathering systems that could be employed to evaluate and influence irrigation programming and cycles. The decision to irrigate must be made on an informed basis. Too frequently irrigation practices fail because they have been established by habit or calendar reference dates. Good irrigation practices should be dictated on a day-to-day basis, by specific turfgrass needs, soil characteristics, projected weather conditions and the purpose and function of the area to be irrigated. Thus, the criteria affecting the decision making process concerning irrigation involves a dynamic, ever changing set of conditions which all must be assessed prior to application. (Sharples, 1999)

Every turfgrass manager must begin (if not already) to implement a programme of water conservation and wise management of this finite resource. The immediate results will be savings in cost. Less water will be consumed, which will result in reduction of the pound spent for the water and the cost to pump and transport it. But, more importantly, it will help the turf manager prepare for the day when it will become necessary for him/her to function with less water. Perhaps the water will simply not be there, physically in the current quantities or because some bureaucratic or legislative authority will have diverted it to a purpose considered more politically important.



AGROCLIMATOLOGY of South East London

Soil Type for purposes of report - Sandy Loam

Table 1 Monthly average figures for climate of South East London

Month

Day length (hrs)

Solar radiation MJ/m2

Temperature 0C

Rainfall mm

Saturation vapour

pressure

kPa

Wind speed mph

Humidity %

Max

Min

January

8.0

2.9

7

2

60

0.758

9

85

February

9.7

5.4

7

2

35

0.758

9

82

March

11.5

9.0

10

3

50

0.935

10

79

April

13.6

13.9

12

5

43

1.002

10

75

May

15.4

18.0

16

8

45

1.357

9

74

June

16.5

18.7

20

11

45

1.599

8

75

July

16.0

19.1

22

13

45

1.818

8

75

August

14.4

16.8

22

13

43

1.818

8

76

September

12.4

11.3

18

11

43

1.498

9

79

October

10.3

7.1

14

7

73

1.228

9

82

November

8.5

3.6

10

4

45

0.935

8

85

December

7.5

2.3

8

3

64

0.872

9

86


Total or Yearly Average

12.0

10.7

10

591 mm year

1.214

9

79


Source - UK Meteorological Office

1. TYPICAL MANAGEMENT REGIME

The components of a management regime for a football pitch revolve around the basic operations of mowing, aeration and fertilisation, of which this report focuses upon, but, there are many other aspects of maintenance that need to be applied to meet the performance requirements of the surface.

Generally, the demands made upon the pitch in terms of performance characteristics and appearance, also the amount of play and wear received will ultimately determine the level of maintenance required.

(a) Mowing

Pederson (1985) found that the Evapotranspiration (ET) rates of cool season grasses increased with mowing height.

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 transpirational loss. Cool season grasses such as perennial ryegrass (Lolium perenne) tend to have vertical leaf orientations and high leaf extension rates, these tend to aid the retention of water by reducing evapotranspirational loss.

Mowing the surface to a height somewhere between 25 - 38mm, the former being typical of the summer months and the latter the winter months, will be the most time labour intensive mechanical operation carried out during the season (STRI, 1994), typically once or twice per week and often after match play. It has been found that the mowing operation has an important effect on the following:

(i)Root and shoot development and hence the density and wear tolerance of the soil. Generally, it can be assumed that the root depth is proportional to the leaf height and that mowing encourages tillering of the turfgrass plant.

(ii)Cylinder mowers with rollers may flatten the grass. This is important, as a cleaner cut will be achieved if the grass is upright. Lying grasses will smother weaker emergent ones producing ultimately a thinner turf and possibly encouraging weed ingress through the promotion of a shaded micro-climate.

(iii)The botanical composition of the sward. For each grass species there is a minimum height of cut at which it can survive. Mowing effects weed populations and type of weed. Under close cutting only low growing weeds can survive such as the rosette types (daisy, plantain), types with surface runners (clover), underground runners (sedges) and mat forming types such as pearlwort and chickweed.

(iv)If cuttings are 'boxed off' then more fertiliser is required to restore soil nutrients. Allowing cuttings to fly produces a more drought resistant sward of better colour. On the other hand, it produces a softer turf more susceptible to disease and favours an increase in worms, weeds and weed grasses.

(Adapted from Winter Games Pitches, STRI, (1994))

Waddington et al. (1993) found that shorter roots (see i) may reduce potential water use because of a reduction in the available soil water reservoir. It follows that shorter roots have the effect of increasing the net irrigation requirement because of the need to retain moisture in the upper 5 - 10 cm of the soil surface where they are located.

Steinegger et al. (1993) have shown that grass mown with a sharp mower actually had an increased total water use of 20 - 30% when compared to a turf mown with a dull mower blade. The reduced water use of turf mown with the dull mower, however, was actually associated with a reduction in shoot density, leaf density, and less growth.

After reviewing available research data, Shearman (1985) concluded that frequent mowing with sharp blades at modest mowing heights offered the best compromise of mowing effects on water use and turf quality while maximising water conservation and turf performance.

(b) Compaction relief and aeration

Vehicular and foot traffic on turfgrass can result in major damage to turf sites. Especially on sports pitches. Traffic problems are of four general types: soil compaction, wear, rutting or soil displacement, and divoting. All of these affect percentage crop cover, essential for irrigation modelling.

Waddington et al., (1992) found that compaction can influence the turfgrass plant by affecting root growth, shoot growth, nutrient uptake, plant water use, stress tolerance, disease incidence and establishment.

These plant responses will dramatically influence the maintenance programmes of turfgrass sites receiving compaction. Such sites cannot be adequately maintained without a high degree of expertise by the turfgrass manager, additional maintenance inputs and extensive labour. Carrow and Troll (1981) detail the numerous ways that a maintenance programme can alter with compaction.

Many of the alterations in soil physical properties compaction causes can adversely influence irrigation programming. For example, reduced infiltration and percolation would result in longer irrigation cycles, greater run-off, and a higher percentage of evaporation loss.

Using perennial ryegrass, evapotranspiration declined under compacted conditions. (Sills & Carrow, 1983; O'Neil & Carrow, 1983). Evapotranspiration decreased by 20% over a season with a 3.5 to 11% reduction during the hottest period. (O'Neil & Carrow, 1983) Thus, a major influence of compaction on turfgrass is a decrease in water usage.

Aeration and de-compaction of soils through the deployment of equipment such as spikers, scarifiers and sub-soil aerators is required to:

(i)Relieve soil compaction and subsequent problems.

(ii)Improve surface drainage

(iii)Improve soil/atmosphere gaseous exchange.

(iv)Increase utilisation of water by the roots.

(v)Encourage deep and extensive root growth.

(vi)Increase the drought resistance of the grass species, and

(vii)Encourage and assist in the breakdown of organic material such as thatch.

(c) Fertilisation

Any cultural practice that increases leaf surface area, internodes length, and vertical extension rate should also increase the water usage. Nitrogen fertilisers increase shoot growth and it can be assumed that increased water would be utilised by the grass plant under high N regimes.

Feldake et al. (1983, 1984) showed that Smooth-stalked meadow grass grown under deficient N level (4 kg N 1000m2 yr -1) had lower ET levels than when N was applied at 4 kg N 1000m2 mo -1). This is attributed to the slower growth rate and lighter green colour (which reflected energy) of the N deficient turfgrass.

There is little information to be found on the effects of macronutrients on turfgrass water usage, the writer believes that there is a great demand for further research in this area. At this time, research data is limited concerning the influence of P and K on the water requirements of turf grasses. Potassium fertilisation increases drought, heat, and cold and disease resistance. The mechanics of which are not well understood. Potassium increases root production (Marklund & Roberts, 1967) which, may, in itself, increase the available soil water reservoir but also the potential consumptive water use of turf.

The influence of P on turfgrass drought tolerance, avoidance and water uptake is also not well understood, and along with K water interaction and processes with the grass plant could be dependant and interactive with other nutrients applied.

Annual nutrient applications for a high class football pitch with clippings boxed off in order to produce a firm surface are displayed in Table 2

Table 2 Annual nutrient applications on a first class football pitch

N

-

160 - 200 kg/ha --1 *

P205

-

80 - 100 kg/ha --1 *

K20

-

80 - 100 kg/ha --1 *

* depending on soil analysis



(STRI, 1994)

The Sports Turf Research Institute, (1994) found that generally, high class football pitches would receive four or five nutrient applications. The first being in March, the second at the end of the playing season, one or two during the summer with one being two weeks before the start of the playing season, and one late in September to mid-October. Half of the Phosphate and/or Potassium annual application would be given at the end of the playing season, before renovation work, and the second half in the Autumn to promote hardy growth in the turf grasses.

On sports pitches of high or pure sand construction the annual nitrogen application rate should be increased to 250 kg/ha -1, and if ordinary soluble granular fertilisers are used then the number of dressings should be increased to six or seven times per year.

(d) Other significant management practices

(i)Top Dressing

(ii)Irrigation

(iii)Repair of divots

(iv)Line marking

(v)Weed and disease control

(vi)Over-seeding

(vii)Brushing

2. PLANT DEVELOPMENT

Waddington et al. (1993) report that turfgrass growth and development is restricted to a specific temperature range (Fig. 1)

Fig. 1 Turfgrass growth and temperature stress zones from Waddington et al. 1993



phils-irra-graph.jpg


There is little biological activity above 500C or below 00C (Leopold & Friedman, 1975). While most plant activity occurs between 100C and 400C, the optimum temperature for maximum metabolic activity or growth differs among plant species and even among cultivars. (Beard, 1973)

From this we can assume that the optimum growth temperature for cool season grass species is 200C. The average temperature for the hottest month last year in SE London was 160C, suggesting that optimum growth rates encouraging maximum leaf area are an infrequent occurrence.

We can also assume that winter temperatures will allow some, all be it slow, growth of the turfgrass plant. Although again, Beard, (1973) suggests any growth occurring at temperatures under 100C is likely to be that of root rather than shoot growth. He goes on to say that a significant amount of root growth occurs with cool season grasses during the winter period if the soil temperature stays above 60C.

The depth of the turfgrass root system will vary through a playing season with soil and air temperature, moisture levels and availability, time of year and management. Generally, extensive deep rooting occurs during the warm wet months of spring and autumn. FAO, (2000) found that typically cool season grass roots will (under ideal conditions) root to depths between 0.50m and 1.0m. Most suspended water table sports turf root zone mixes facilitate root growth to depths of 30 - 40cm. Beard, (1973) found that during the summer in periods of heat or drought stress rooting activity ceases until more favourable growing conditions occur.

Another factor that needs mentioning while discussing the relationships between temperature variations and growth of the turfgrass plant is the microclimate. Most first class football pitches will have surrounding stadia. Beard (1973) states that trees, buildings and other objects alter the thermal balance between turf and its surroundings. The writer feels the conditions and subsequent problems associated with this are beyond the scope of this paper. Although the writer suggests that this inevitably will alter the crop coefficient vales (addressed later in report).

3. EVAPOTRANSPIRATION & CROP COEFFICIENT'

Brown, (2000) states that the rate of ET for a given environment (vegetation) is a function of four critical factors. The first and most critical is soil moisture. Evaporation (ET) simply cannot take place if there is no water in the soil. However, if adequate soil moisture is available, three additional factors - plant type, stage of plant development and weather - affect the ET rate. The four weather factors are; solar radiation, wind speed, humidity and temperature.

Humidity and temperature work in tandem to determine the drying power of the atmosphere. The vapour pressure deficit (VPD) is the meteorological variable used to state this. Brown (2000) states that Relative Humidity (the humidity variable most commonly reported), is a poor indicator of atmospheric dryness. As an atmosphere with a 30% relative humidity and a 860F temperature is 2 times that of an atmosphere with the same 30% relative humidity and a 680F temperature.

Allen et al. (1998) state, when assessing the ET rate, additional consideration should be given to the range of management practices that act on the climate and crop factors (discussed in 1.) affecting the ET process. Also, that cultivation practices and the type of irrigation method can alter the microclimate, affect the crop characteristics or affect the wetting of the soil or crop surface.

It is therefore reasonable to presume that a first class, highly maintained football pitch surrounded by stadia (acting as a wind break) will significantly reduce the ET potential of the turf and soil during windy, warm conditions.

Allen et al. (1998), describe reference evapotranspiration (ET0) as the ET rate from a reference surface, not short of water. This reference surface is a hypothetical grass reference crop with special characteristics.

Doorenbos & Pruitt (1992) define ET0 as the rate of evaporation from an extensive surface of 8 to 15cm tall, green grass cover of uniform height, actively growing, completely shading the ground and not short of water.

Allen, Smith et al. (1994) provide a more precise definition of reference evapotranspiration:

The rate of evapotranspiration from a hypothetical crop with an assumed height of 12cm, a fixed canopy resistance of 70 s m-1, and an albedo of 0.23

The crop coefficient of this crop would be 1.

Reference evapotranspiration (ETo) therefore only relates to a hypothetical surface. The 'potential crop evapotranspiration', (ETc or ETp) is the sum of transpiration and soil evaporation for a healthy plant, at a particular stage of growth and not short of water, and, 'actual evapotranspiration' (ETc) depends upon the resistance to water movement through the stomata, therefore this is dependant upon the soil water content.

Turfgrass crops tend to exhibit three stages of growth, firstly, 'initial' secondly, 'crop development' and thirdly, 'mid season'. Where as all other crop types exhibit four, the final being 'late' or 'end'. Perennial ryegrass used on first class football pitches has a life cycle of two or more growing seasons. The grass spends most of its growing life in the 'mid season' stage, rarely flowering due to the mowing regime.

The author was unable to locate data suggesting suitable lengths of growth stages that would enable Kc values to be calculated for each. On sports turf surfaces crops are managed very intensively while developing. Satisfactory values for growth stages would prove to be extremely difficult to estimate with no empirical supporting data. Although, with several years of weather data and turfgrass water use rates, crop coefficients could be determined and a specific crop curve developed and calculated.

Allen et al. (1993) specify that in the crop coefficient approach the ETc is calculated by multiplying the ETo by a crop coefficient (Kc).

ETc = Kc x ETo (1)

Brown, (2000) States that the stage of plant development plays a critical role in determining ET. The more immature the plant the more water is lost via evaporation and conversely the more mature the plant (the denser the canopy) the more water will be lost through transpiration.

Brown, (2000) found that actual turf water use (ETT) is rarely measured in the real world. Instead, meteorological data and mathematical models are used to work out the data for us. These models are known as the Penman or Penman-Monteith equation. These measure then estimate the reference evapotranspiration (ET0).

However, these predictions are sensitive to the accuracy of the input data measured. (Hess, 1996)

In practice turf is rarely grown that mimics the surface and soil conditions described. However, we can adjust the ET0 value taking into account the turf type, quality and stage of development. The adjustment process is to multiply the ET0 by an adjustment factor that is known as a crop coefficient (Kc) see figure 2. The crop coefficient is basically the ratio between ETo and ETc.

Thus: ETT = Kc x ET0 (2)

Fig. 2 Reference evapotranspiration (ET0) must be adjusted with a crop coefficient (Kc) to estimate turf ET (ETT): from Brown & Kopec, (2000)

phil-sharples-irra.jpg


Calculation of the ETo, using the Penman-Monteith method was considered viable and could be used as a reference because it is based upon a hypothetical grass surface, of fixed height, albedo and surface resistance. Any first class, managed, football surface would exhibit similar qualities.

Calculations for the reference evapotranspiration are summarised in Table 3.

Table 3 Monthly ETo calculated from the climatic data in table 1.

Month

Penman-Monteith mm/month

Penman mm/month

January

3.2

9.4

February

10.6

19.4

March

28.3

41

April

51

67.7

May

79.6

100.2

June

90.7

109.3

July

98.6

121

August

82.7

106.2

September

45.7

63.7

October

20.3

35.3

November

5

13.2

December

1.8

6.7

Summer (av.)

79.4

100

Winter (av.)

5.1

12.1



The Kc in equation 1 predicts ETc under standard field conditions (disease free, well fertilised, and grown in large fields, under optimum soil water conditions). The ETc predicted by Kc should be adjusted to non-standard conditions, ETc adj, where any environmental condition or characteristic is known to have an impact on or limit the ETc. (Allen et al. 1998)

Non-standard field conditions (ETc adj) include conditions as the presence of pests and diseases, soil salinity, low soil fertility, water shortage or water logging and will encorporate sportsturf field conditions such as compaction. These conditions affect turf and would need consideration.

Arizona State University have carried out tests on two species of cool-season turfgrass, Tall fescue (Festuca arundinacea) and Perennial ryegrass (Lolium perenne) It was found that appropriate Kcs for Tall fescue grown at 40mm during the summer months range from 0.80-0.95. This range would seem to support the general rule that cool season turfgrass use significantly more water than warm season.

Ryegrass varieties are frequently oversown into bermudagrass swards during the Autumn as the bermuda becomes dormant to retain a green winter turfgrass surface. Arizona State University found appropriate Kcs for ryegrass' (cut at a height between 17 - 30mm) during this period to be 0.65 - 0.75. Brown & Kopec, (2000) suggest lower Kcs are appropriate for less dense stands of grass and during colder periods when frosts are common, and higher Kcs are appropriate for warmer months and where high levels of fertiliser generate dense, fast growing stands of turfgrass.

For the purposes of this paper, the author feels it appropriate, due to the lack of data supporting Kc values within the context of first class football pitches, to use the Kc values obtained by Arizona State University. The general mowing heights reflect to a degree the sward heights found on football pitches and the tested turf was managed.

Fig 3 The Kc range for cool season turfgrass during summer is 0.80-0.95. Use higher Kcs for high quality turf and turfs with less heat tolerance. Lower Kcs suffice for lower quality turf or for more heat tolerant varieties: from Brown & Kopec, (2000)

phils-irrigationm.jpg


Fig 3.1 Monthly crop coefficients appropriate for use with ETo. Computed by weather stations/networks using the Penman-Monteith approach. The turf surface from November through May is sown with ryegrass. October is missing as overseeding occurred. It is interesting to note the higher levels of Kc during the periods of Perennial ryegrass cover.

Month

Estimated Crop Coefficient

January

0.78

February

0.79

March

0.86

April

0.89

May

0.85

June

0.78

July

0.78

August

0.82

September

0.83

November

0.83

December

0.8

Winter

0.83

Summer

0.8



Density and turf height are other factors that can have an impact on the Kc value. Taller turf use a little more water than closely cropped as they interact more effectively with the atmosphere (wind and solar radiation). This is a result of the increase in leaf surface area. Literature and research showing definite results for the effect of cutting height and Kc value was not found by the author.

Density of turfgrass cover -having a high impact on ETc values- varies on high quality football pitches greatly, from >95 - <50%. This is dependant upon factors such as amount of hours played on the surface through training or match play, budget available for management, construction type and climatic conditions encountered. Generally, wear patterns and loss of canopy are concentrated in the goal-mouth areas.

Having evaluated the research material and data in this paper the author in figure 3.2 suggests Kc values that may be appropriate use within the South East of London. This would allow calculation of ETc. Irrigation planning and scheduling could then be devised.

Fig. 3.2 Suggested Kc values for estimation of ETc in South East London.

Month

Suggested Kc values for SE London

January

0.68

February

0.75

March

0.8

April

0.85

May

0.89

June

0.95

July

0.98

August

0.93

September

0.83

October

0.8

November

0.7

December

0.65

Winter (av)

0.74

Summer (av)

0.91



4. RESPONSES TO SOIL WATER CONDITIONS

If not watered adequately during the course of a growing season turf may be exposed to water deficits. These deficits vary in their severity and duration. How the grass plant responds to water deficits, explains, to a great extent, the survivability of turfgrass.

The effects of water logging on turfgrass areas can include:

(i)Restricted root growth

(ii)Reduced transpiration

(iii)Ultimately death

(iv)Increased incidence of disease

(v)Leaching

(vi)Pollution of groundwater

(vii)De-stabilisation of the soil structure

(viii)Changes in species composition

(ix)Reduced playability of the surface.

Soil water conditions are illustrated by Figure 4.

Fig. 4 Soil water moisture terms and conditions

phil-sharples-irra-4.jpg


Wilt is the drooping, rolling or folding of turfgrass leaves resulting from a loss of turgidity. It occurs when the transpiration rate is greater than the rate of water absorption by the root, but it is only temporary and can be corrected with the application of water. (Danneberger, 1993)

The transpiration potential of turgid, photosynthesising grass leaf blades is relatively inflexible. Turfgrass wilts when it does not receive sufficient rainfall or irrigation to meet transpirational needs. Witling of turf is often aesthetically unacceptable. (Waddington et al. 1973)

Wet wilt is the wilting of turf when soil moisture is high. In situations where soils are water logged, roots cannot take up moisture because of a deficiency of oxygen. Wet wilt occurs most frequently on waterlogged and/or compacted soils. It has a significant effect on shallow rooting species such as annual meadow grass (Poa annua). (Danneberger, 1993)



Danneberger, (1993) goes on to define drought as a prolonged water stress that limits or prevents turfgrass growth. Drought severity depends upon the duration of periods without rainfall or irrigation, the evaporative demand of the atmosphere and water holding capacity of the soil.

The major disadvantages to droughted conditions include:

(i)Loss of presentation/aesthetics

(ii)Reduction in leaf production

(iii)Death of the plant

(iv)Proness to hydrophobicity

(v)Wasted nutrients as they are not dissolved and utilised by the plant

(vi)Salt accumulation

Drought conditions can severely affect the playing characteristics of a football pitch. Leaf wilt and shrinkage exposes the soil surface increasing the rate of evaporation, resulting in increased surface hardiness affecting ball bounce and pitch playing characteristics. Surface resilience and traction properties will be affected. Player injuries, especially those associated with abrasion of the skin and lower leg (ankle and shin) are also likely to increase through this.

Saturation of the root zone or water logging generally results in increased tearing of the grass plant from the soil surface, reduction in the number of and the density of roots, destructing of the soil as compaction increases from play, surface capping and shallow rooting depths. As discussed earlier, the likelihood of plant death increases with the extent and duration of the saturated conditions.

Waddington et al. (1992) found that grasses appear to be more tolerant of poor soil aeration than other agronomic and horticultural crops. Finn et al. (1961) grew Timothy (Phleum pratense), Brome grass (Bromus inermis) and canarygrass (Phalaris arundinacea) at several soils water contents and found them to be quite tolerant of saturated soil conditions and low O2 diffusion rates. It was also found that perennial ryegrass exhibited deeper root systems than many grasses under high water table conditions.

The writer has found that positive responses of yield to waterlogged conditions have generally been maintained through application of Nitrogen, and that this application has generally been used to mask any effects of water table depth on grass yields. Waddington & Baker (1965) suggested that liberal fertilisation may account for similar yields being found when grasses were grown under various soil aeration conditions. Grable (1966) concluded that the principle requirement for high yields of grasses grown in poorly aerated soils is adequate fertilisation to compensate for fewer roots, less root activity, or both.

(a) Soil conditions for irrigation scheduling:

Irrigation is required when rainfall is insufficient to compensate for the water lost by evapotranspiration. The primary objective of irrigation is to apply water at the right period and in the right amount. By calculating the soil water balance of the root-zone on a daily basis, the timing and the depth of future irrigations can be planned.. To avoid crop stress situations, irrigation should be applied before or at the moment when the readily available soil water is depleted. To avoid deep percolation losses that may leach nutrients out of the root-zone, the net irrigation depth should always be smaller than or equal to the root-zone depletion. (Allen et al. 1998)

Key terms referred to with soil moisture status are:

(i)Field Capacity - The water content of the soil where all free water has been drained through gravity.

(ii)Permanent Wilting Point - The soil moisture content at which the plant will wilt and possibly die. There will remain water in the soil but the plant will be unable to extract it for use.

(iii)Total Available or Readily Available Soil Water Content - The difference between the amount of water in the soil at field capacity and the amount at wilting point.

(iv)Saturation - Occurs when all the voids within the soil are completely filled with water. Although there is plenty of water available for the crop, uptake is seriously impaired by the lack of oxygen in the soil.

(v)Readily or Easily Available Soil Water - Only a portion of the available water is easily used by the crop. The maximum soil water deficit is the amount of water stored in the plants root zone that is readily available to the plant. When the soil water content drops below a threshold value, soil water cannot be transported quickly enough toward the roots. This threshold is known as the Critical Soil Water Deficit. This manageable allowable depletion factor for turfgrass is 0.40.

(MAFF - British Colombia, 2002)

The water holding characteristics of a Sandy Loam and other soil textures soil are illustrated in Figure 5.

Fig 5 Graph illustrating the critical water storage characteristics of soils of different texture: From MAFF.

phils-irra-5.jpg


FAO (56) states the soil water characteristics for Sandy Loam soils are;

Field Capacity 180mm/m - 280mm/ m

Wilting Point 60mm/m - 160mm/m

(USA Soil Classification)

For the reference site the critical soil water deficit was plotted to allow for reference of ETc and therefore adjustment to the irrigation planning and cycle. (fig. 6) This then forms the basis of any irrigation cycle initiated.

Table 4 Calculations to determine critical soil moisture deficit. Data from table 12, FAO 56. Maximum rooting depth taken from typical depth of rootzone used for a football surface.

Available water content of soil 120mm m- 1

Maximum rooting depth

0.35 m

Maximum potential SWD

42 mm

Soil Depletion Factor

0.4mm

Critical SWD

16.8mm



Fig. 6 Effect of soil water deficit on relative evapotranspiration. Plotting from this graph allows the ETc value to be obtained. The CSWD for the sandy loam = 16.8mm

phil-6.jpg
5. MANAGEMENT & IRRIGATION STRATEGIES

The first most and most important decision used with irrigation strategies will be to decide 'when to apply water' and 'how much to apply'. Irrigating a soil too late or in too small an amount reduces yield production, makes inefficient use of fertiliser and affects the quality of the crop. (Hess, 2002)

Irrigate 'too much' or 'too early' and money is wasted pumping (energy), money is wasted on the cost of water, the risk of water logging is increased, nutrients are leached and traffic ability problems can arise. (Hess, 2002)

The objective of irrigation scheduling is to maintain 'optimum' soil water conditions for growth. This optimum for sports turf use has historically meant maximum leaf growth and colour but should mean for optimum use of water and highest crop quality.

The maximum amount of water applied at any one time should be enough to bring the soil back to field capacity. Any more will result in a loss to drainage and therefore wastage. The maximum amount applied for each irrigation cycle should be equal to the soil water deficit at the time of irrigation. This ensures the plant or crop is never stressed, is allowed to grow to its full potential and encourages a deep and extensive root system to develop.

Whilst the readily available water determines the maximum irrigation amount, the optimum amount applied may be dictated by the design of the irrigation system. Therefore, the optimum irrigation depth should be selected upon the basis of the system used as well as the soils (Pereira, 1996)

The calculation of irrigation requirements gives the amount of water required during any time period. Having calculated the required net irrigation depth, the intervals between is given by;

I = d/ETc

i = irrigation interval (days)

d = Net irrigation depth (mm)

ETc = crop water use (mm/d)

(Hess, 2002)

The root depth and possibly the allowable depletion, change through the season, therefore the net irrigation depth may not be constant.

All irrigation schedules utilised on sports turf areas should be modified to allow for;

(i)Weather fluctuations (ETo, rainfall)

(ii)Changes in root activity and sensitivity to stress

(iii)Efficient use of rainfall

Most sports turf areas should initiate 'Real Time' irrigation scheduling. The idea here is to determine when the soil has dried to its allowable lower limit (critical soil water deficit), and to predict this in advance. The trouble is that the climate in the South East of England has wet and dry periods, making irrigation continually stop and start. The methods of determining the soil water status are based upon:

(1)Crop indicators

(2)Soil Water Content

(3)Soil Water Potential

(4)Agro-Climate modelling

This report has focused on Agro-Climate modelling aspects, but, the best approach toward irrigation scheduling is to be aware that all methods currently used for estimating crop and atmospheric water use have their limitations. Use a combination of methods to determine soil water, measuring the soil water tension, soil water content, or measurement by 'feel'. The status of water in the plant can be measured through appearance or growth rate. Keep a close eye on the weather forecasts and trust in your instincts, years of formal knowledge of how the sward reacts to soil water conditions are irreplaceable.

6. REFERENCES



Allen, R.G., Pereria, L.S., Raes, D. & Smith, M. (1998) Crop evapotranspiration - Guidelines for computing crop water requirements. FAO Irrigation & Drainage Paper 56. Rome: FAO. http://www.fao.org/docrep/X0490E/x0490e00.htm#Contents. (Accessed 06.03.02)

Beard, J.B., (1973). Turfgrass: Science & Culture. Prentice Hall, Englewood Cliffs. NJ

Brown, P.B. (2000). Basics of evaporation and transpiration. University of Arizona Turf Irrigation Management Series 1: From: http://ag.arizona.edu/azmet/phxturf.html. (Accessed - 06.03.02)

Brown, P.B. & Kopac, D. (2000). Converting reference evapotranspiration into turf water use. The University of Arizona Turf Irrigation Management Series 2. http://ag.arizona.edu/pubs/water/az1195.pdf (Accessed - 06.03.02)

Carrow, R.N., & Troll, J. (1991). Management of high traffic areas. Proc. 50th University of Mass. Turf Conference. p.1 - 10

Doorenbos, J. & Pruitt, W.O. (1992) Guidelines for predicting crop water requirements. FAO Irrigation and Drainage Paper 24

Grable, A.R. (1966) Soil aeration & plant growth. Adv. Agron. 18:57 - 106

Feldake, C.M., & Danielson, R.E., & Butler, J.D. (1983) Turfgrass evapotranspiration. I. Factors influencing in urban developments. Argon. J. 75:541 - 544

Feldake, C.M., & Danielson, R.E., & Butler, J.D. (1984) Turfgrass evapotranspiration. II. Responses to deficit irrigation. Agron. J. 76: 85 - 89

Hess, T. (2002) Irrigation Scheduling class notes. Module G67. March 2002.

Leopold, A.C., & Kriedemann, P.E. (1975) Plant growth and development. 2nd Edition. MaGraw-Hill. New York

O'Neil, K.H., & Carrow, R.N. (1983) Perennial Ryegrass growth, and water use under soil compaction and N fertilisation. Agron. J. 75: 488-492

Marklund, F.E., & Roberts, E.C. (1967) Influence of varying nitrogen and potassium levels on growth and mineral composition of Agrostis palustris Huds. P. 53. In Agronomy abstracts. ASA, Madison, WI.

Martin, E.C. (2001). Methods of determining when to irrigate. The University of Arizona Turf Irrigation Management Series 30. http://ag.arizona.edu/pubs/water/az1220.pdf

Meteorological Office UK - http://www.met-office.gov.uk/climate/uk/averages/sites (Accessed 06.03.02)

MAFF, British Columbia, (2002) Soil water storage capacity and available soil moisture. Water Consevation FactSheet 550. Revised February 2002. Order number 619.000-1

Pereria, L.S. (1996) Inter-relationship between irrigation scheduling methods and on-farm irrigation systems: In Irrigation Scheduling: from theory to practice. Water Report 8. FAO Rome. pp91 - 104

Sharples, P.M. (1999) Saving Water. In: Greenkeeper International. April 1999 pp 55-70

Sills, M.J. and Carrow, R.N. (1983) Turfgrass Growth, N use, and water use under soil compaction and N fertilisation. Agron. J. 75: pp 488 - 492

Shearman, R.C. (1985) Turfgrass culture and water use. p 61 - 70. In V.A. Gibeault and S. T. Cockerham (ed.) Turfgrass Water Conservation. Univ. of California, Riverside. Publ. 21405

Steinegger, D.H., R.C. Shearman, T.P. Riordan & E.J. Kinbacher. (1993) Mower blade sharpness effects on turf. Agron. J. 75:479 - 480

The Sports Turf Research Institute (STRI) (1994) Winter Games Pitches: The construction and maintenance of natural turf pitches for team games. pp 193. ISBN 1-873431-03-1

Waddinton, D.V., Carrow, R.N., & Shearman, R.C. (1992) Turfgrass. p 229 - 309. American Society of Agronomy Inc. Madison, WI, USA

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