Fertiliser

There are 17 essential chemical nutrients required to achieve optimal plant growth. They are classified according to the quantity required by plants as either macronutrients or micronutrients (trace elements).

For each essential nutrient, plants have a sufficiency range within which optimal growth can be achieved. Nutrient concentrations higher or lower than the sufficiency range adversely affect plant growth through either toxicity or deficiency. These usually cause visual symptoms on plant leaves, in addition to deterioration in plant health and growth.

Basic Nutrients: Carbon (C), Hydrogen (H) and Oxygen (O).
Plants obtain these nutrients from carbon dioxide in the atmosphere and from soil water, unlike all the other essential nutrients which are absorbed from the soil via the roots. The basic nutrients are required in the greatest quantities, but are almost never deficient.

Primary Nutrients: Nitrogen (N), Phosphorous (P) and Potassium (K).
Primary nutrients are the ones most commonly deficient in turf and therefore the ones most commonly supplied in turf fertilisers.

Nitrogen helps give your turfgrass a deep green colour, and promotes high leaf and stem growth at the expense of root growth. Grasses need N more than any other nutrient in the fertiliser you apply, though species vary in the amount of N they require. Avoid excessive nitrogen, however, as this will increase mowing frequency, water demand, thatch build-up and susceptibility to insects and disease.

Phosphorus is needed for turfgrass root growth, and is important for turfgrass establishment. In the absence of a specific soil test, clovers and medics (which need higher levels of P for growth than grasses) can provide a guide as to your soil phosphorus status. If you already have a number of healthy clover or medic plants in your lawn, it is a safe bet that you do not need to apply additional P in fertiliser. Otherwise, apply moderate amounts through your fertiliser program.

Potassium helps improve the health of your turfgrass through better disease resistance, winter hardiness, and drought and traffic tolerance.

In general, turfgrasses require nitrogen, phosphorus and potassium (NPK) in roughly a 3-1-2 ratio. After basic soil deficiencies have been corrected, a 3-1-2 ratio fertiliser is a commonly used in most maintenance programs.

Secondary Nutrients: Calcium (Ca), Magnesium (Mg), Sulfur (S)
Secondary nutrients are required in smaller quantities than primary nutrients. Calcium and Magnesium are usually found in sufficient quantities in soil, particularly if dolomitic limestone is used. Sulfur is often supplied as a component of fertilisers.

Micronutrients are essential nutrients required in very small amounts. They are: Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Molybdenum (Mo), Chlorine (Cl), Nickel (Ni). Except for Fe, turf deficiency in micronutrients only occurs in special circumstances.

Soil acidity varies according to soil type. The degree of soil acidity is indicated by pH numbers ranging from 1-14 (pH 7.0 = neutral; pH <7.0 is acid; pH >7.0 is alkaline). For turfgrass, a pH of 6.0 to 7.0 is desirable.

Maintaining a proper pH for your lawn grass is important, because soil pH determines how the soil nutrients are used. Fertilisers work much better when you keep the proper pH.

Soil fertility focuses on nutrient-soil interaction. The soil system is comprised of four components: Inorganic constituents, Organic matter, Biological entities, and Pore space. Soils have chemical, physical and biological properties that are either beneficial or detrimental to turf grass growth.

One of the most important chemical properties of soils is the Cation Exchange Capacity (CEC). The CEC is a measure of the amount of cations (positively charged nutrients) that a soil can hold and are potentially exchangeable for plant uptake. Basically, sands have the lowest CEC compared to sandy loams (medium) and heavy clays (high. Plant available nutrients are held in either the soil water or attached to soil particles.

Pore spaces are the voids within the physical matrix of a soil. They are described as either macro-pores (aeration pores) or micro-pores (moisture retention pores) and are essential for water retention and movement, gas exchange and channels for root growth.

The CEC, and physical nature of your soil will influence the time in which nutrients are available to your turf grass. In a sandy soil with excess irrigation or large rainfall events, plant nutrients held in the soil solution are quickly leached beyond the turf grass root system. In a clay soil, with less drainage, nutrients in the soil solution will leach more slowly. Nitrogen, as well as potassium and other nutrients, is easily lost due to leaching.

Inorganic fertiliser
Inorganic fertilisers are usually granular, slow-release, or liquids and contain varying quantities of N, P and K, other macronutrients and trace elements. The N-P-K ratio and chemical analysis displayed on fertiliser bags will state the quantities of nutrients contained in each preparation.

Granular or powdered fertilisers are water-soluble and will “dump” all of their nutrients when watered into your lawn. These nutrients are immediately available to plants. At high application rates or with too little irrigation, particularly during the heat of the day, fertiliser burn can occur through excess nutrients on the leave. Usually, leaf tips will show the burn first.

When a fertiliser containing high amounts of nitrogen is applied, turf grasses can go into a growth flush, followed rather quickly by a “trough”. If using these types of nitrogen fertilisers, it is best to reduce the application rate and apply more often.

Slow-release fertilisers have either resin coatings or sulfur and polymer coatings around small balls of plant nutrients. Technology has developed to a stage that these coatings provide a reliable method of feeding your turfgrass over an extended period. The coatings soften after becoming wet, slowly releasing their nutrients over time. This method of fertilising has a higher purchasing cost. However, they save labour by reducing the number of applications needed, are less likely to cause leaf burn, and provide nutrients at rates that do not cause excessive growth flushes. The fertiliser bags will contain their nutrient analysis and the longevity of release.

Modern slow release fertilisers commonly have a mixture of slow release and soluble nitrogen to provide an initial “green-up” followed with continuing N response from the slow release component.

Liquid fertilisers act in the same way as granular or powdered fertilisers. Their nutrient contents are immediately available to plants and are exposed to leaching once in the soil solution. These types of fertiliser can be applied as a drench to the soil system or as foliar spray. A foliar spray is applying the fertiliser at the recommended rate to the plant leaves, with the nutrients absorbed into the plant via the leaves. Liquid fertilisers can be more expensive than granular fertilisers and may contain less plant nutrients.

Organic fertilisers
Organic fertilisers typically consist of composted plant material, animal manure, blood and bone meal, sewage sludge, marine plants (kelp), fishmeal or other materials derived from a natural source rather than a chemical source. They can be a mulch, pelleted or liquid preparation.

Organic mulches are applied to the turf surface, or incorporated into the soil surface before planting. Pelleted organic fertilisers are applied to the turf surface. Both mulch and pelleted organic fertilisers should be watered-in after application to your lawn. Liquid preparations can be applied as a soil drench or foliar spray. Soil drenches are exposed to leaching once in the soil solution.

Organic fertilisers can contain all or some of the essential plant nutrients, but usually in lower percentages than found in inorganic fertilisers. For example, chicken manure has an N-P-K ratio around 3.5-2.5-2.5. The benefits of organic fertilisers are that they are slow release, providing long lasting nutrition, are an excellent source of minor elements, and may contribute to the health of the soil by promoting microbial activity. Organic fertilisers made from composted animal manures need to be well composted before applying to a lawn. If the composted mulch is not well aged, applied at high rates or not watered in after application, turfgrass foliage is likely to be burnt by excess nitrogen. A very fresh manure smell will indicate the mulch is “hot” and should be aged further or applied at light rates and thoroughly watered-in.

Seawater contains all known nutrients in solution. Kelp fertilisers will contain all plant nutrients in ratios as they were found in the kelp. These organic preparations supply plant nutrients, and plant hormones at ratios similar to those found in terrestrial plants, which may benefit plant health.

Fertilisers come in different strengths and composition. All have three numbers on their label, which indicate the composition of fertiliser materials. The first number shows the percent of nitrogen. The second number indicates the percent of phosphate. The third number lists the percent of potassium (potash).

A mixed fertiliser has nitrogen (N), phosphorus (P), and potassium (K) combined. For example, a N-P-K ratio of 16-4-8 states that the fertiliser contains (by weight) 16% nitrogen, 4% phosphorus, and 8% potassium. A ratio of 21-0-0 for N-P-K shows this preparation contains only nitrogen and no phosphorus or potassium.

Micronutrients and impurities are also usually listed as part of the chemical analysis.

A large range of fertiliser is available for turf, with the following table indicating the macronutrient ratios found in a sample of these products. (This table is not an endorsement of these specific fertilisers, but rather an indication of different ratios).

Table. Analysis ratios of fertilisers used on home lawns:

Product type and Name N P K S Ca
Granuular, high nitrogen
Urea 46 0 0
Nitram 34 0 0
Gran-Am 0 0 0
Granular, complete
CK88 15.1 4.3 11.5 13.6
Q 5 5.3 5.5 5 3.3 12.8
Nitrophoska Blue 12 5.2 14.1 4 4
Tropic 10 3.4 6.4
Slow Release, complete
Turf Gold 22 2.1 4.1
Sportturf Fertiliser plus 2%FE 24 2 9
SportsMaster high N 22 2.2 8.3
Scotts Lawn Builder 27 1.3 3.3
Osmocote Lawn Food 28.2 2 7
Organic, complete
Dynamic Lifter Turf Master 9.9 4.3 6
Organic Plus Lawn Food 14 2 10

The best fertiliser strategy keeps your lawn growing at a slow and steady pace. Application rates should be as low as possible and still produce a quality lawn. Over-fertilising weakens your lawn and causes excess growth. Therefore, it is best to fertilise lightly more often, rather than once at a high rate.

Follow the recommended application rate for the fertiliser you are using. All fertilisers have different analysis, so they may vary in the recommended rate. Nitrogen is the most important nutrient for turf grass and they will require more frequent applications of N than any other nutrient.

Iron deficiency in turfgrasses is the most common micronutrient deficiency, particularly on blue couch. Iron chlorosis (yellowing) appears in newly developed leaves. There are many causes of iron deficiency in turfgrass, but the most common are nutrient imbalances in the soil, high soil pH, poor root system reducing uptake, and excessive nitrogen fertilisation.

Developing an effective fertiliser program for your turfgrass depends on three things:

  • Which grass you are growing
  • Where you live in
  • What kind of fertiliser is available

Soil and leaf tissue testing is the only accurate way to calculate the amount of fertiliser required by your home lawn. Soil and leaf test results will usually include details of fertiliser type, amount and application timing for your lawn. Other than using testing laboratories, general recommendations need to be followed.

Turfgrasses can be fertilised while they are actively growing during the spring, summer and autumn. As a general rule, fertilise a few weeks after the weather has warmed up after winter, till a few weeks before the weather cools down. Turfgrass will not utilise much fertiliser during the cold months of the year, with soil reserves enough to hold them through until spring. Keeping your turf healthy and actively growing during March and early April will help your turf hold better colour during the winter months.

The frequency of fertilising depends primarily on the type and form of nitrogen used. Granular fertilisers will last between 4 and 8 weeks, slow release fertilisers will depend on the longevity stated on the bag.

It is best to apply fertiliser during the early morning or late afternoon. If fertilisers are applied during the hottest part of the day you increase the chance of foliage burn. Always irrigate your lawn after applying fertiliser, although not enough to cause run-off. Irrigating for several times over a few days, rather than all at once is a good option.

Fertiliser spreaders are an excellent way to spreader granular and slow release fertilisers.

The spreaders usually have calibrations that will allow you to adjust the flow, depending on the prill size and/or application rate. A plastic bucket and your hand is also a perfect way to spread fertiliser. When spreading fertiliser by hand you must try and spread the fertiliser as evenly to avoid a patchy result. Plastic gloves should be worn when handling any chemicals, including fertilisers.

To apply foliar fertiliser you can use a hand-held garden sprayer. These sprayers should not be used to spray both herbicides and fertilisers as plant damage may result. Foliar fertilising is an excellent way to adjust the nutrient status of a turf grass plant. Micronutrients such as Fe and Mn, are the most common foliar treatments for turf grasses. During periods of high stress N, K, Fe and Mn can be applied as a foliar spray or when high rain or sandy soils cause excessive nutrient leaching of N, K, and Mg.

Content included on this page has been modified; original content was published in Lawns and Lawn Care, a homeowner’s guide (no date) and on the web by the former Dept of Primary Industries and Fisheries. Permission for use has been granted by the now Dept of Agriculture and Fisheries.

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