When we talk about fertility management on golf course greens, most people think of nitrogen, phosphorus, and potassium. As we see more greens built with sand-based root zones, superintendents need to pay closer attention to the secondary elements and micronutrients. Even in older greens that have been topdressed with sand for years, the primary growing medium is some mix of predominately sand.

The secondary elements include calcium, magnesium, and sulfur. We rarely think of managing these elements because they are often in ample supply in soils. Calcium and magnesium, however, are two elements that are prone to leaching in very sandy soils, and are often deficient. Sulfur levels are usually related to organic matter content, which is usually very low in new sand based root zones. Sulfur is also prone to leaching in sandy root zones with little organic matter.

While they are called secondary elements, calcium and magnesium are required by turfgrasses in amounts comparable to phosphorus. They are every bit as essential as the primary nutrients: nitrogen , phosphorus, and potassium.

Calcium is a component or cofactor in several enzymes, a component of cell walls, and is involved in cell division. Research conducted as long ago as the 1930’s reported the benefits of calcium on root hair development in colonial bentgrasses. More work conducted in the 1960’s showed that colonial bentgrass was more susceptible to Pythium blight where calcium was limiting. The role of calcium in reducing root disease caused by Pythium species is well documented in other crops.

The sand type used to construct or topdress greens will influence the need for calcium. Silica sands are chemically inert, and usually contain little if any calcium. Calcareous sands may contain up to or more than 20% calcium carbonate (limestone), the limestone actually being a component of the sand fraction. These high pH sands should have more than adequate amounts of calcium present in available form.

There has been little research published that refers to critical soil or plant tissue levels for calcium. Therefore, specific recommendations for rates can only be speculative. There are many sources of calcium, however, that can be used.

Sands that are deficient in calcium often have a low pH. In these cases, test the pH of the sand or root zone, and apply the appropriate rate of calcitic or dolomitic lime. If a pH change is not wanted, gypsum is an option, as are several other sources. Certain phosphate fertilizers contain calcium. Natural organic fertilizers derived from bone meal or poultry litter are also good sources of calcium. Table 1 lists fertilizer sources for calcium and several other nutrients.

Magnesium is an essential nutrient that is in the center of the chlorophyll molecule; the pigment that gives plants their green color. Magnesium is also involved in the activity of several enzymes. The fact that we are seeing more specialty greens fertilizers with magnesium suggests that there is a need for this nutrient in sand culture. Based on my own experience, greens deficient in magnesium usually appear anemic. They often lack color, density, and vigor. Superintendents will report that the greens don’t respond to nitrogen or iron. In such cases, soil or tissue analysis usually verify low magnesium.

Aside from inherently low magnesium in the soil, magnesium deficiencies may be induced by excessive amounts of potassium. Therefore, unless potassium deficiencies are known to exist on the green, apply potassium at rates not to exceed the rate of nitrogen.

Several sources of magnesium are available for use. Some of the more conventional sources include dolomitic limestone, magnesium sulfate (Epsom salts), potassium magnesium sulfate (Sul-Po-Mag) as well as many specialty fertilizers. Like calcium, there is no good information on critical magnesium levels in soils and plant tissue.

Fertilizer recommendations for potassium, calcium, and magnesium can be made based on a soil’s ability to hold these nutrients. These three nutrients are called basic cations because they have a positive charge associated with them. Clay and organic matter in a soil have negative charges that hold these nutrients in exchangeable form. This means that as nutrients are removed from the soil solution by leaching or plant uptake, these nutrients will come off the exchange sites into solution.

The soil’s ability to retain these nutrients depends on the number of these negative charges, or the cation exchange capacity (CEC) of the soil. New sand/peat root zone mixes rarely have CEC values in excess of 2 meq/100 grams of soil. Modified soils that might exist in your topdressing layer may have a CEC in excess of 10. The CEC of a root zone or soil should dictate how much potassium, calcium, and magnesium you need to add to your greens.

The base saturation is the ratio of the cation exchange sites that should be occupied by potassium, calcium, and magnesium. The base saturation is often used as a guideline in determining these nutrient needs. While these target ratios may vary from lab to lab, potassium should occupy 2 to 7% of the exchange sites, magnesium 10 to 20%, and calcium 65 to 85%. These values serve only as a guideline, pointing out where there may be deficiencies or imbalances.

The base saturation and CEC combined can be used to determine your application rate. The table below lists the amount of nutrient a root zone or soil with a known CEC can hold.

CEC	Potassium lb/1000 sq ft	Magnesium lb/1000 sq ft	Calcium lb/1000 sq ft
2	0.9	0.8	7.3
5	2.5	2.1	14.9
10	3.2	3.7	29.8

You can see from the table above what a profound effect the CEC has on the amount of these three nutrients a soil can hold. If you are maintaining new sand based greens, potassium rates in excess of 1 lb per 1000 square feet may be too much. Like pouring a gallon of water into a 1/2 gallon jug, you will have waste. In a green, it could be lost to leaching or luxury consumption by the plants. Spoon feeding your new greens or using slow release fertilizers will be your best approach, especially for potassium.

Even slight increases in the CEC of a soil can make a big difference in how you manage your fertility, and how easy it will be for you to do so. Soil testing provides the best means of assessing the needs of these three basic cations where some reserve is present in the soil.

Sulfur deficiencies in soils are rare, but responses to sulfur may be possible on sand-based greens, especially in areas of high precipitation. Sulfur is a component of several proteins, so limiting amounts of sulfur may result in a loss of vigor and reduced growth.

Young greens in particular may benefit from occasional applications of sulfur. As organic matter accumulates in the soil, however, the need for supplemental sulfur should become minimal. Additions of sulfur to bentgrass greens have been reported to reduce the incidence of Fusarium patch, reduce annual bluegrass encroachment, and reduce the incidence of black algae.

In some parts of the country, significant amounts of sulfur are added to greens as acid rain. Several fertilizer sources of sulfur are available as well, and these are listed in Table 1. On new bentgrass greens, apply sulfur at annual rates of 1 to 2 lbs of sulfur per 1000 square feet. Be aware that phosphate and other fertilizers will contribute small to moderate amounts of sulfur. While sulfur tests are not routinely run by soil testing labs, requesting this test will provide you with a better guideline for determining sulfur rates.

Except for iron and manganese, there has been very little research conducted on micronutrient nutrition in bentgrass. From a practical standpoint, iron is the most widely used micronutrient on greens. Involved in the synthesis of chlorophyll, iron is most often deficient in alkaline greens or in greens that have high levels of phosphorus or manganese. Iron deficiency appears as yellowing or chlorosis of the newly emerging leaves. This contrasts to nitrogen deficiency, where the chlorosis occurs in the older leaves. Light applications of iron will produce a darker green color in the turf, even where it is not deficient. In many cases, iron is used as a supplement to nitrogen; superintendents reducing nitrogen but attaining darker color through iron applications.

There are two main sources of iron used for greens fertilization: ferrous sulfate and chelated iron. Ferrous sulfate is a soluble iron source. When applied to turf as a foliar spray, the response to ferrous sulfate is very rapid. Granular applications of ferrous sulfate may be less efficient, especially on alkaline soils because the iron would be quickly converted to insoluble, unavailable forms.

Chelated iron is a complex organic compound that is a more stable carrier than ferrous sulfate. It takes longer to break down in the soil, so the length of response is longer than ferrous sulfate. Since iron is immobile once in the plant, the length of iron response is dependent on growth rate regardless of the source.

An application rate of 0.5 ounce of elemental iron per 1000 square feet is adequate to produce the desired response. Rates in excess of this normally are not necessary, and may produce an excessively dark, even black appearance.

Manganese is another element that has gained attention in recent years. The role of manganese in the plant is as an activator of several enzymes. While deficiencies are rare, positive responses to manganese applications have been observed. In studies conducted at Cornell University several years ago, it was found that biweekly applications of manganese at a rate of 0.5 ounces per 1000 square feet produced a positive response in growth and quality. This was true on both calcareous and low pH sand greens. As the rate was increased to 1.5 ounces per 1000 square feet every two weeks, the quality and growth rate continued to increase on the alkaline sand green, but decreased on the low pH sand. These results suggest that toxicities may occur at this rate on low pH greens.

The most common sources of manganese are manganese sulfate and chelated manganese. Aside from these fertilizer manganese sources, also realize that an application of the fungicide Fore (mancozeb) will add about an ounce of manganese per 1000 square feet per application.

When managing micronutrients, you should be as concerned with toxicities as with deficiencies. Fertilizers that offer a full compliment of micronutrients in balanced proportions offer the most logical approach to micronutrient management. Avoid fertilizers that are high in any one micronutrient. Where deficiencies or toxicities are suspected, tissue testing is an affective means of assessing micronutrient status.

As sand becomes a predominant growing medium on greens, micromanagement of primary, secondary, and micronutrients will play an important role in the performance of these greens.

Table 1: Secondary nutrients and common fertilizer sources

Essential Nutrient	Nutrient content
Calcium	% Calcium
Calcitic limestone	53%
Dolomitic limestone	22%
Gypsum	22%
Superphosphate fertilizers	14 to 20%
Certain natural organics	7 - 23%
Magnesium	% Magnesium
Dolomitic limestone	12%
Potassium magnesium sulfate	11%
Magnesium sulfate	10%
Sulfur	% Sulfur
Gypsum	19%
Ammonium sulfate	24%
Potassium magnesium sulfate	18%
Potassium sulfate	18%
Superphosphate	12%
Sulfur-coated products	12 to 24%
Elemental sulfur	100%

[From Grounds Maintenance article]