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Fertilizer Practices

       

 KEY CONCEPTS
• Nitrogen and phosphorus can adversely affect water quality through the stimulation of aquatic algae and weeds and degrading the water as a potable supply.

• Nitrogen is highly susceptible to being lost from turf areas through:
- volatilisation;
- leaching;
- surface runoff; and
- removal off-site through grass clippings.

• Phosphorus has low solubility and is principally lost from turf areas through the movement of soil particles.

• Phosphorus leaching can occur on soils with a low phosphorus retention index (eg. sandy soils), or with ongoing phosphorus loading that is in excess of plant requirements.

• Turfgrass systems have a high capacity to absorb and retain nutrients and prevent their loss to the wider environment.

• Reclaimed water containing plant nutrients can provide an alternative fertiliser source.

• The potential for nitrogen and phosphorus losses can be significantly reduced by:
- using slow release fertilisers, and
- fertilisation using ‘spoon feeding’—that is, applying a little fertiliser often.

• Avoid fertilising if rainfall is expected.

• Use soil and plant tissue testing to monitor fertiliser requirement.

• Use soil sensors to monitor soil nutrient levels and water application.

 

Contents

5.1 The environmental impact of using fertilisers on turf
5.1.1 Nitrogen losses from turfgrass systems
5.1.2 Phosphorus losses from turfgrass systems
5.2 Soil and plant tissue testing
5.3 Sources of nitrogen fertiliser
5.4 Fertigation
Case study
References

5.1 THE ENVIRONMENTAL IMPACT OF USING FERTILISERS ON TURF

The maintenance of golf courses relies on the well-regulated use of both fertilisers and water so that high-quality playing surfaces are produced. Lush, green and vigorously growing turf swards are undesirable for golf as these surfaces are usually soft, slow and prone to attack by insects and disease. Australian golf courses have traditionally been maintained to minimise inputs so that firm, fast and tight surfaces are produced.

5.1.1 Nitrogen losses from turfgrass systems

In turfgrass systems, nitrogen is generally of most importance from a water quality perspective (Walker and Branham 1992). Petrovic (1990) has provided the most comprehensive review on nitrogen losses in turfgrass systems and provides information on the development of best management practices to prevent groundwater deterioration. He stated that nitrogen will escape from local nutrient cycling systems in turfgrass through:

• gaseous processes including volatilisation from applied fertiliser and denitrification;
• leaching from the rootzone;
• surface runoff; and
• removing grass clippings off-site, potentially a significant source of nutrient loss from the turfgrass nutrient cycle.

Volatilisation

Ammonia volatilisation is known to occur rapidly following the application of urea (Bowman et al. 1987). The losses due to volatilisation cited by Walker and Branham (1992) have ranged from 10% to 39% in closed system experiments and from 9% to 41% in field experiments. The variation depends on climate conditions (e.g. higher volatilisation in hotter, low humidity conditions) and the irrigation method used (e.g. fine spray irrigation increases volatilisation). Other forms of nitrogen such as ammonium nitrate and sulfurcoated urea exhibit very little loss by volatilisation.

Denitrification

During soil saturation conditions, soil mineral N levels can be reduced by the conversion of nitrate N into gaseous N forms, N2 and N2O, which are lost to the atmosphere (Peverill, Sparrow and Reuter 1999).

Mineralisation

Organic N (in soil organic matter) is released to plants through microbial processes into mineral forms, predominantly ammonium (NH4 +) and Nitrate (NO3). Increasing the duration of moist and warm soil conditions will have varying affects on the opposing soil processes of mineralisation (transforming soil organic N into mineral N) and immobilisation (transforming soil mineral N into soil organic forms) and thus on net mineralisation of soil N (Peverill, Sparrow and Reuter 1999).

Leaching

The degree of nitrate leaching from turfgrass systems is variable (Petrovic 1990), depending on soil type, irrigation, nitrogen source and rate and time of year applied. Some researchers have reported little or no leaching while others have measured 80% or more of applied nitrogen. Walker and Branham (1992) compiled a table of the available research on nitrate leaching in turfgrass systems. It is important to note that many of the experiments were based on single and relatively high nitrogen applications, and in several of the studies the nitrogen applications are several times greater than what would be expected to be used on typical New South Wales golf courses.

Overall, the leaching losses and the nitrate concentrations were relatively low. However, one particular study showed significant leaching to a depth of 3 metres with nitrate concentrations in excess of 50 mg/L (Exner et al. 1991). The contributing factors causing this leaching were high irrigation applications (51 mm every third day) and a high nitrate
concentration (10 mg/L) in the irrigation water. This study demonstrated the importance of not applying excessive amounts of water that leach the nitrate out of the root zone before turf uptake.

Environmental studies funded by the United States Golf Association (Snow 1996) reported in the USGA Green Section Record (Vol. 33(1), 1995). Yates (1995) demonstrated that on a sand/peat putting green, with nitrogen applied at 0.5 kg N/100 m2 month, 0.56–1.69% of the applied nitrogen leached through the turfgrass. In a fairway situation, on a loamy sand soil with the nitrogen applied at 0.25 kg/100 m2 /month, the losses were 0.30–0.75%.

Brauen and Stahnke (1995) examined the leaching of nitrate on sand profiles where nitrogen was applied at 2, 4 and 6 kg N/100 m2 year either monthly or every two weeks and found that application at 4 kg N/100 m2 /year resulted in little or no nitrate leaching.

The important contributing factors were:
• 70% of the nitrogen being in a slow release form;
• fertilising at 14-day intervals at reduced rates; and
• having a mature turf with a good root system and some accumulation of organic matter.

In a monitoring study of nitrate and pesticide leaching beneath golf courses on sandy soils at Cape Cod, Massachusetts, Cohen et al. (1990) observed nitrate concentrations in the groundwater ranging from 0.1 mg/L to 30 mg/L. Nitrate concentrations did not exceed the drinking water standard of 45 mg/L (10 mg/L nitrate-nitrogen). It was also found that
subsurface losses of nitrogen were reduced when slow release fertilisers were used and application rates were reduced.

Irrigation practices are seen as having an important influence on the leaching of nitrogen. Various studies have been undertaken and where irrigation is uncontrolled and excessive, the leaching losses are generally high (Petrovic 1990). Conversely, where soil moisture sensors are used to monitor/control irrigation, the leaching losses are very low.

The other significant factor affecting leaching losses was the timing of fertilising. Leaching losses are increased during periods of cool weather and high rainfall. Cool temperatures in particular reduce plant uptake as well as reduce denitrification and microbial immobilisation. Fertilising before high rainfall events can result in large losses of nitrogen.

The transport of nutrients in surface runoff is a potential means for the movement of nutrients off-site. However, in the limited publications concerning runoff from turfgrass, nutrient transport was significantly reduced by turfgrass systems (Douglas et al. 1995). In trials undertaken on a sloping site (9–11% slope), with a nitrogen application rate of 4 kg N/100 m2 year and subjected to an irrigation event of 150 mm/hr, there was little or no movement of nitrogen in the runoff water (Douglas et al. 1995). The key factor influencing surface runoff was turf density, where a dense turf consisting of a stoloniferous grass species increased the resistance to overland flow, increasing the opportunity for infiltration of water and trapping of nutrients in the thatch/organic layer. Concentrations of Nitrate-N and Kjeldahl-N rarely exceeded 7 mg/L and 2 mg/L respectively and generally the nutrient loadings reflected those found in the irrigation water.

5.1.2 Phosphorus losses from turfgrass systems

Phosphorus is essential for turfgrass health and growth, but if incorrectly applied or overused it can create environmental problems. Plant nutrients in waterways can initiate serious algal blooms and the growth of other aquatic weeds. While a range of factors contribute to nuisance algal and weed growth, they can occur with relatively low nutrient levels in the waterbody. ANZECC & ARMCANZ (2000) provides guidance and water quality criteria that can be used to assess the risk of adverse effects of nutrients. The risk of nuisance aquatic algae/plant growth is increased when ambient nutrient levels in the waterbody exceed the ‘trigger values’ given in Table 5.1. See ANZECC & ARMCANZ (2000) for guidance on the use of ‘trigger values’ and management of nuisance plant and algae growth in waters.

The movement of phosphorus in surface runoff is usually associated with the movement of soil particles. Most well-established golf courses have a solid vegetation (turf) cover that greatly reduces surface runoff and effectively eliminates soil movement. On construction sites or disturbed areas, management practices that minimise soil movement should be used. These include preventative measures as well as appropriately placed and maintained sediment controls such as sediment traps and barriers, and silt fences and straw bales. Buffers and sediment controls adjacent to waterways are particularly important to minimise potential impacts on surface water resources. For further information on sediment controls see NSW DECC (1998) Managing Urban Stormwater: Soils and Construction (the 'Blue Book').

The phosphorus sorption capacity of a soil relates the process by which phosphorus binds to the soil, thereby becoming unavailable for leaching or run-off. Different soil types have a varying capacity to sorb phosphorus. Sandy soils, for example, generally have a limited capacity to retain phosphorus. Once soils reach phosphorus saturation, any additional
phosphorus (dependent on its form), may be leached deeper into the soil profile and the underlying watertable. The process of leaching starts to occur before the full P-sorption capacity of the soil is reached. Soil analysis, in particular measuring the phosphorus retention index (PRI), is used to indicate a soils P-sorption capacity. Measuring the PRI is
desirable on sandy soils. Most soil test interpretations have a minimum phosphorus concentration that can often be at phosphorus saturation for that particular soil.

5.2 SOIL AND PLANT TISSUE TESTING

Soil and plant tissue testing is widely used in turf management for several purposes (Carrow 1995):
• identifying nutrient deficiencies;
• predicting nutrient needs for adjustment by fertilisation;
• evaluating potential excesses or imbalances of essential nutrients, heavy metals or salts;
• assessing other important soil chemical aspects such as pH, organic matter content, salt status and cation exchange capacity that may influence turfgrass growth; and
• environmental monitoring.

Annual soil and tissue testing provides a very useful means of fine-tuning the fertiliser program and determining the effectiveness of amendments that have been made previously.

The elements normally tested in soils include pH, electrical conductivity (salinity), phosphorus, potassium, and exchangeable cations (calcium, sodium, magnesium and potassium). While micronutrients can also be tested for, their relevance to plant uptake is questionable.

Plant tissue analysis provides an excellent complement to soil testing and gives the best indication of plant-available nutrients, particularly micronutrients. Where controlled release fertilisers are used, particularly potassium, soil tests can often give unexpected, low results.

As the controlled release nutrient is released to meet plant requirements, there is little excess nutrient to be adsorbed onto the soil particles; consequently, the nutrients often show up to be excessively low. On the other hand, in the same situation, plant tissue analysis often indicates adequate amounts of nutrients in the plant and therefore completes the soil–turfgrass relationship.

Plant tissue analysis usually includes analysis for nitrogen, phosphorus, potassium, calcium, magnesium, sodium, chloride, sulfur, manganese, boron, copper, zinc and iron.

The application of nutrients and soil amendments has become a refined maintenance practice and is used to produce firm, fast, high-quality golfing surfaces. Soil and plant tissue testing is a worthwhile investment to manage the fine edge between high-quality surfaces and turfgrasses that are weak, lack density and are susceptible to disease.

THE VALUE OF SOIL AND PLANT ANALYSIS
In looking at the average fertiliser use on greens and fairways, the costs (including labour, materials and equipment) are about $25,000–35,000 p.a. If soil and plant tissue samples were taken from three representative greens and fairways (i.e. 6 soil tests and 6 plant tissue analyses), the cost would be about $1,056. The cost of testing is therefore about 3–4% of cost of the fertiliser program. This is a relatively small cost if you consider:

• the cost of an unnecessary or inappropriate fertiliser application;
• the fact that analysis is an integral part of the integrated pest management program;
• that good turf nutrition results in good, healthy turf that requires fewer pesticides. One less application of fungicide would cover the cost of the testing program; and
• that analysis provides a method for monitoring salts and sodium where low-quality water is used. Early diagnosis of high salinity and
sodicity allows for appropriate treatments to be initiated to prevent turf damage and costly renovations/rejuvenation.

5.3 SOURCES OF NITROGEN FERTILISER

Nitrogen sources can be divided into two categories: readily available (high solubility) and slow release (low solubility) sources. Soluble nitrogen sources are highly susceptible to leaching losses. On sandy soils or sites that have a shallow watertable and sites with geologic pathways to the groundwater from cracks, rocks or high pedality, nitrogen leaching beyond the root zone and into the watertable is a greater risk. Controlled release fertilisers have been used to reduce these losses.

Inorganic salts: Applications of inorganic salts (e.g. ammonium nitrate) to turfgrasses usually produce a rapid initial flush of growth of short duration. In the absence of large leaching or volatilisation losses, the efficiency of uptake is relatively high, however, within three weeks after application, up to 20–30% of the applied N can still be recovered from the root zone (Turner and Hummel 1992). This indicates that there is still opportunity for leaching losses to occur. On putting greens with high sand content, the technique of ‘spoon feeding’, which provides very low application rates of nutrients, is often used. This procedure encourages consistent growth patterns and greatly minimises losses due to leaching.

Slow release: There are several forms of slow release fertilisers, including organics, synthetic organics and coated fertilisers. Natural organics include a range of products such as animal manures and activated sewage sludges. Processed poultry manure has been a popular form of organic fertiliser and contains about 3–5% nitrogen. Organic fertilisers are slow release in nature and rely on the release of nitrogen by microbial breakdown of the complex organic molecules; however, the release rate is relatively unpredictable.

Synthetic organics include urea formaldehyde reaction products and isobutylidene diurea (IBDU). Urea formaldehyde is typically marketed with a portion of nitrogen that is watersoluble and causes a quick response in the turfgrass. IBDU has very little soluble component and may take some time to initiate a response. It is very important when selecting slow or controlled release fertilisers that the turf manager understands the responses to quick and slow release forms of nitrogen.

Coated nitrogen sources are made by coating urea or other soluble nitrogen sources with a semi-impermeable coating. Sulfur is frequently used, often with a polymer or resin coating. Sulfur-coated urea is a very effective fertiliser and has proven to be cost-effective on ‘broadacre’ turf.

The release rate for controlled release forms of nitrogen is affected to varying degrees by temperature, moisture and microbial activity. It is therefore important that the turf manager understands the fertiliser–environment interactions so that the desired outcomes are achieved.

As a proportion of the golf course, the fairways represent the greatest potential for nitrogen losses through leaching. Fairways are fertilised infrequently, usually with relatively high quantities of nitrogen. It is not convenient or cost-effective to ‘spoon feed’ fairways unless fertigation is used. However, the use of inorganic forms of nitrogen makes fairways
susceptible to leaching losses if a high rainfall event occurs soon after application. Neylan and Robinson (1997) demonstrated that on sand profiles an inorganic nitrogen source was depleted within five days of application following heavy irrigation. In this situation, the nutrients were leached directly into the watertable.

Because of the leaching potential and possible environmental impacts, there is a justification for using controlled release fertilisers on sand-based fairways in conjunction with other irrigation management practices such as controlling the leaching fraction with irrigation scheduling and soil moisture sensors. Advantages of controlled release fertilisers are:

• that less frequent applications are required;
• that leaching losses are reduced; and
• they promote more even growth patterns.
Perceived disadvantages of controlled release fertilisers are:
• their high cost; and
• lack of longevity of some products under tropical conditions.

5.4 FERTIGATION

Fertigation involves injecting nutrients into the irrigation system at controlled, low concentrations. This allows for the ‘spoon feeding’ of large areas of turf while greatly reducing labour and equipment costs. It also allows the turf to be fertilised at night and therefore reduces the inconvenience to golfers.

Because of the water quality on many golf courses, in particular high sodium, gypsum injection into the irrigation system is common. The equipment permits the addition not only of gypsum but also of various fertilisers and wetting agents.

CASE STUDY: Cost/Benefit Analysis of Fertigation

The following case study is a cost/benefit ananlysis comparing the use of fertigation as a method of fertilising and applying soil amendments.

1 Fertiliser application

Fertiliser:          Potassium nitrate
Area:                   20 ha
Labour:                Using injection system — 1.5 hours
                         Application by conventional spreader — 6 hours
Labour cost:         Injection system — $1.50/ha
                         Conventional — $6.00/ha
Machinery cost:     Conventional — $50.00/ha

Potential benefit is $54.50/ha/application. If 4–6 applications are made over a year, the benefit is $218–327/ha or $4,360–6,540.

2 Gypsum application
Premium grade fine gypsum for injection system:   $420/tonne
Application rate:                                                  5 t/ha/year
Cost of applying gypsum through injection system: $2,100/ha
Area:                                                                 20 ha
Total cost:                                                          $42,000
Conventional supply and spread to apply 
gypsum at 5 t/ha $250/ha                                   Total cost $5,000

The gypsum injection unit costs about $17,000. Based on using it for fertilising, the payback period is 2.6–3.9 years.

There is a direct economic benefit to be gained from using the injection system for gypsum applications on fairways, as well as other benefits:
• greater efficiency of application. Soluble gypsum reacts more quickly and moves deeper into the profile;
• the system allows small quantities to be applied often, improving the reaction in the soil and counteracting the regular applications of sodium in the water;
• no large machinery is used on the golf course; and
• no golfer complaints are received about gypsum on the turf.


REFERENCES

ANZECC and ARMCANZ 2000, Australian and New Zealand guidelines for fresh and marine water quality, Australian and New Zealand Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra, ACT, Australia.

Beard, J. B. 1973, Turfgrass Science and Culture, Prentice Hall Inc., New Jersey. Bowman, D.C., Paul, J.L., Davis, W.B. and Nelson, S.H. 1987, Reducing ammonia volatilisation from Kentucky bluegrass turf by irrigation. HortScience 22(1): 84–87.

Brauen, S.E. and Stahnke, G.K. 1995, Leaching of nitrate from sand putting greens, USGA Green Section Record 33(1): 29–32.

Brown, K.W., Duble, R.W. and Thomas, S.C. 1977, Influence of management and season on fate of N applied to golf greens, Agron. J. 69 (4): 667–671.

Brown, K.W., Thomas, J.C. and Duble, R.L. 1982, Nitrogen source effect on nitrate and ammonia leaching and run-off loss from greens, Agron. J. 74(0): 947–950.

Carrow, R. 1995, Soil testing for fertiliser recommendations. Golf Course Management 62(11): 61-68.

Cohen, S. Z., Nickerson, S., Maxey, R., Dupuy, A. and Senita, J.A. 1990, Ground water monitoring study for pesticides and nitrates associated with golf courses on Cape Cod. Ground Water Monitoring Review 10(1): 160-173.

Douglas, T., Linde, T., Watschke, T.L. and Borger, J.A. 1995, Transport of run-off and nutrients from fairway turfs, USGA Green Section Record 33(1) 42–44.

Exner, M., Burbach, M.E., Watts, D.G., Shearman, R.C. and Spalding, R.F. 1991, J. Environ. Qual. 20(3): 658-662.

Handreck, K and Black, N. 1994, Growing Media for Ornamental Plants and Turf, University of NSW Press, Sydney.

Johnston, K. J. 1996, Turf Irrigation and Nutrient Study: Turf Manual, Royal Australian Institute of Parks and Recreation, Western Australia Region.

Neylan, J., and Robinson, M. 1997, Sand amendments for turf construction, International Turfgrass Research Journal, 8:133-147.

New South Wales Department of Housing and New South Wales Environment Protection Authority 1998, Managing Urban Stormwater: Soils and Construction, Department of Housing, Sydney.

Petrovic, A.M. 1990, The fate of nitrogenous fertilisers applied to turfgrass, J. Env. Qual. 19(1): 1–14.

Petrovic, A.M., Hummel, N.W. and Carroll, M.J. 1986, Nitrogen source effects on nitrate leaching from late fall nitrogen applied to turfgrass, Agron. Abstr. p. 137.

Peverill, Sparrow and Reuter (eds) 1999, Soil analysis – An interpretation manual, CSIRO publishing, Collingwood, Victoria.

Sheard, R.W., Haw, M.A., Johnson, G.B. and Ferguson, J.A. 1985, Mineral nutrition of bentgrass on sand rooting systems, in Proc. 5th Int. Turf Res. Conf., France, pp. 469–485.

Snow, J.T. 1996, An overview of USGA environment research, in Proc. Environmental Issues in Turf: A Symposium, ATRI publication.

Snyder, G.H., Burt, E.O. and Davidson, J.M. 1981, Nitrogen leaching in Bermuda grass turf, in Proc. 4th Int. Turf Res. Conf. Guelph, Ontario, Canada, pp. 185–193.

Snyder, G.H., Augustin, B.J. and Davidson, J.M. 1984, Moisture sensor-controlled irrigation for reducing N leaching in bermudagrass turf, Agron.J. 76(6): 964–969.

Starr, J.L. and De Roo, H.C. 1981, The fate of nitrogen fertiliser applied to turfgrass, Crop Sci. 21(4): 531–535.

Turner, T.R., and Hummel, N.W. 1992, Nutritional requirements and fertilization, American Society of Agronomy, 32:385-439.

Walker, W.J., and Branham, B. 1992, Environmental Impacts Turfgrass Fertilisation, Golf Course Management and Construction: Environmental Issues pp105-221 Edited by J. Balogh and W. Walker. Lewis, Chelsea, MI.

Yates, M. 1995, The fate of pesticides and fertilisers in a turfgrass environment, USGA Green Section Record 33(1) 10–12.