Magazine - Nutrition of Sand Greens Part 1.

By Jerry Spencer in Consultancy on 5th Nov 2008 6:00

Jerry first begun his turf career as an agronomist at the (STRI) Sports Turf Research Institute in the UK and has since held roles as head Agronomist for Turf Force Pty Ltd, Business and Technical development manager for Paton Fertilizers and Technical product Manager for Arthur Yates and Co.
Author of over 60 published articles both here and in the UK, Jerry has also written the "Definitive guide to Australian Pesticide Management"

The nutrition of pure sand constructions raises a whole host of issues but there are a number of rules that are can be applied and can help guide you in the right direction. Sand-based putting greens are less forgiving than native soil greens when it comes to nutrient management, having inherently lower nutrient-holding and -buffering capacities and allowing large amounts of water to flow through them. As a result, they are prone to multiple, sudden and perhaps serious nutrient deficiencies.

Part 2 Can be found by clicking here - www.pitchcare.com.au/magazine/article/772

Nitrogen management Nitrogen (N) stands apart from all other nutrients with regard to its impact on turfgrass growth. Turfgrass actually exhibits shoot-growth responses all the way up to 7.5kg N per 100m2 or more. However, for several reasons turf managers generally use just 1 to 2.5 kg per 100m2. In reality, most turf managers maintain their sward in a constant state of N deficiency by adopting a ‘lean and mean’ fertiliser strategy.

Many factors affect the rate and frequency of N you apply to sand greens. Many turf managers follow the USGA Green Section recommendation of light, frequent N applications - generally in the range of 0.05 to 0.125 kg/100m2 every 7 to 14 days and using water soluble fertilisers. The aim is to promote slow, steady shoot growth that favours the health of the turfgrass and stable putting conditions.

The appropriate interval between light N applications varies with factors such as weather as well as the criteria adopted by the manager. The two most commonly employed criteria are optimising turfgrass colour and minimising the amount of clippings produced. In contrast due to staffing or temporal constraints many clubs are not able to allow for frequent N applications and so their alternative is less-frequent applications at higher rates, for example, 0.25 to 0.4kg /100m2 every 4 to 6 weeks. Superintendents following this strategy often use only granular products.

Both approaches to N application have their place. Light, frequent applications are the norm on courses where golfers demand fast putting greens. By contrast, mowing at heights that provide slower speeds results in conditions more compatible with the use of granular fertilizers and less frequent applications of higher N rates. To say that one N application strategy is better than the other ignores differences in the expected outcomes. Both can result in high-quality playing surfaces.

While it is true that high N rates stimulate shoot growth at the expense of root growth, it also is true that low N rates can lead to reductions in root growth. The annual N rate below which root growth declines is not clearly defined. Some evidence suggests that extensive foliar feeding of N at low rates adversely affects root growth compared to granular fertilizer applications. Superintendents that apply 2 to 2.5kg/100m2 annually aim for high-density turf that rapidly heals from injury. This group of superintendents may also include those who have elected to live with Poa annua. Applying 2 to 2.5kg of N per season provides greater colour uniformity of bentgrass/ Poa annua putting greens.

A great deal of attention is devoted to the virtues of different N carriers with a constant battle being getting a preferred balance between the N-release pattern of the slow-release N material and the proportion of the water-soluble and slow-release components. Choice of N carrier comes down to personal preference although the particular release characteristics of any one carrier should be considered. Light, frequent applications are most convenient to apply in water-soluble form with a sprayer or through the irrigation system.

All slow-release N fertilizers contain some water-soluble N. The question often arises as to what is the best balance between water-soluble and slow-release N. The water-soluble component provides quick turfgrass greenup, and the slow-release component promotes uniform long-term colour. Research suggests that a 1:1 ratio of water-soluble to slow-release N best meets both of these criteria.  Golfer obsession with green speed has impacted the type of fertilizer superintendents apply. Mowing at 3mm or less to gain Stimpmeter speeds of 10 or more resulted in substantial mower pickup of granular fertilizers. Consequently turf managers have responded by shifting to spray applications of water-soluble fertilizers.

Fertilizer suppliers have addressed this by manufacturing smaller fertilizer particles, and many have adopted the practice of reporting the SGN of their products. SGN is the average particle diameter, expressed in millimeters and multiplied by 100. For example, if the average particle size is 1.5 mm, the SGN of the fertilizer is 150.

Mowing greens at 4mm or less calls for an SGN of no greater than 100 to keep mower pickup of the granules to acceptable levels. Now that fertilizers meeting this requirement are being manufactured, the choices of slow-release N carriers suitable for closely mowed greens have expanded. An important additional benefit of smaller fertilizer particle size is greater application uniformity at low rates. For optimal growth to occur, the plant also must take up additional phosphorus (P) and potassium (K). This gives rise to what is known as "nutrient demand."

Several consequences of nutrient demand exist. First, what constitutes an adequate supply of P and K in sand greens varies with the rate of N application. The greater the amount of N you apply, the greater the demand for P and K.  Another consequence of nutrient demand is that when soil levels of P and K already are at levels that satisfy this demand, applying further amounts serves no purpose as although turf may take up these nutrients, a term called ‘luxury consumption’, it can in fact be detrimental and result in for example an induced magnesium deficiency.

Nutrient demand gives rise to a strong linkage among the concentrations of N, P and K in turfgrass shoots. In other words, the N:P:K ratio in the plant tissue is remarkably constant. It will vary somewhat with the time of year and weather, but on an annual basis, it stays close to 9:1:7 for a high-quality creeping-bentgrass putting green. In fertilizer terms, this equates to an N:P:K ratio of 4:1:3.

P Management
In the case of P of particular importance is the carbonate content of the sand used in the construction. Higher carbonate levels reduce P availability. Thus, higher soil-P levels are required to satisfy turf's demand when carbonates are present.  As a general rule of thumb consider 35 ppm (Bray) soil-test P to be a good target level for all sand greens . This avoids having to take into account the carbonate content of the sand. Of course, using this target level for sand greens with no or little carbonate will result in P levels higher than what the turf actually requires. By far the best time for adjusting sand greens to the optimum soil-test P level is during grow-in. If your sand has significant levels of carbonates, this may require monthly applications of starter fertilizer at an N rate approaching 500g N/100m2.

For established greens with suboptimal soil-test P levels, you should consider using starter fertilizer for your first application of the year. If soil tests are very low, starter-fertilizer application should be repeated late in the season as well. Whatever you choose to do, make sure that you keep close track of your soil-test P until you've reached optimum levels.

After you've adjusted soil-test P to its optimum level, the task is to keep it there. How much P you need to apply annually to accomplish this goal depends on how much P you're removing in the clippings. This is where the concept of nutrient demand comes back into the picture. How much P you're removing depends on your annual N rate.  Over time, this program will result in slowly declining soil-test P levels and an adjustment application of P will periodically be necessary. Occasional soil testing will tell you when this is necessary.

K management
Sand putting greens pose special challenges in the management of K levels. Compared to native-soil greens, sand greens have a low capacity to bond K as firstly sand greens, even with organic amendments, have low cation-exchange capacity (CEC). What little CEC exists largely comes from organic amendments, but these typically compose just a small fraction of the mix. Secondly the cation exchange sites in organic matter have a stronger preference for Ca and Mg than for K.
With the low CEC and preferential bonding of Ca and Mg in sand greens, there is a limit to the amount of K that you can load onto the cation exchange sites before leaching losses become excessive. Research has shown that when soil-test K levels rise much above 100 ppm, the concentration of K in the soil solution increases rapidly, and large amounts may leach from greens.

However, 100 ppm of exchangeable K is not enough to meet the full-season demand of turfgrass for K. This tells us that management of K in sand greens requires either multiple applications of the nutrient during the season, which means you have the task of determining frequency and rates of K application or utilising slow/controlled release forms.
To increase turfgrass tissue-K concentrations, an unsatisfied demand for K must exist, or you must create new demand through N application. Applying K alone or applying N and K late in the season (when turfgrass growth is suppressed by low temperatures) offers little chance of increasing shoot-K concentrations. To be effective, you must accompany late-season K applications by N and apply them when the turfgrass shoots are still growing.
The ratio that nutrients are removed by the plant and found in leaf tissue falls in an NPK range from 3:0.25:2 to 8:1:5 (Salisbury, 1995 Street, 1998) although the actual requirements vary depending on turf species and physical form of the fertiliser.

Handreck and Black (1994) proposed that annual NPK applications fall in the following range.

Table 1 Maximum and minimum proposed NPK ranges for optimal turf growth



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Read more articles in Consultancy, by Jerry Spencer or from November 2008.