Guideline Index

Chapter 11. Introducing Fertilisers

11.3 Fertiliser products

Prior to the mid-1960s, only a limited range of fertiliser products was available in Australia. Advances in agricultural and manufacturing technology have resulted in a wider range of fertiliser products, and new terms are now being used to describe the fertilisers on the market.

Today, the term fertiliser is applied to a number of products. Those called inorganic fertilisers (sometimes called commercial, synthetic or artificial fertilisers) mostly contain chemicals with the essential plant nutrients in available forms, the production of which involves some industrial process. Examples include urea, superphosphate and muriate of potash. Organic fertilisers are made up of organic material containing carbon from animal and plant products. Examples of organic fertilisers include: animal manures, dairy and dairy factory effluent (refer to Chapter 13 ), compost and blood and bone.

The main terms used to describe fertilisers are further discussed below.

11.3.1 Low-analysis fertilisers

Low-analysis fertilisers are the less concentrated products. They have a lower percentage of nutrients in their analysis. Examples include single superphosphate. These products are made using a different manufacturing process to that used to make high-analysis fertilisers. As a result, they have higher sulphur levels than the high-analysis fertilisers; and it is usually in the form of sulphate sulphur, which is readily available to plants.

11.3.2 High-analysis fertilisers

High-analysis fertilisers are the more concentrated products. They have a higher percentage of nutrients in their analysis. They cost more per tonne to purchase because they are more concentrated, but spreading and freight costs are reduced because you need less product to apply the same quantity of nutrient per hectare. An example of a high-analysis fertiliser is triple superphosphate.

11.3.3 Straight fertilisers

The term straight fertilisers is a bit misleading and not regularly used. It is more commonly used by the manufacturers in the factories. It is used to describe fertilisers that contain only one of the macronutrients, such as urea which contains nitrogen, or muriate of potash which contains primarily potassium.

Many of the ‘straight’ fertilisers, such as single superphosphate and sulphate of ammonia, also contain other essential nutrients, such as sulphur.

11.3.4 Compound fertilisers

Compound fertilisers are products that have been manufactured by a chemical reaction and contain two or more of the major nutrients. All granules are similar in size and contain the same nutrients. They are generally more expensive per tonne but not on a per kg nutrient basis than mixed or blended fertilisers. Examples include di-ammonium phosphate (DAP) and mono-ammonium phosphate (MAP).

11.3.5 Blended fertilisers or mixed fertilisers

Blended fertiliser is the term applied to fertilisers that are a physical mixture of one or more of the ‘straight’ or compound fertilisers. Examples include SuPerfect Potash 3 & 1, PastureBoosta, Greentop K, and HayBoosta. The fertiliser companies are now able to provide a wide range of blended products to suit specific nutrient requirements. Many of their blends are listed on their product list. You would need to contact them regarding the cost of special ‘prescription blends’; that is, blends with stipulated types and proportions of nutrients (See Appendix F for a range of online product lists, including blends).

The final analysis of blended products will be the result of the overall proportions of the various products not simply an addition of the percentages.

For example: Super Potash 2 & 1 is a blend of two parts single superphosphate (each containing 8.8% P) and one part muriate of potash (which is 50% K). It’s like putting two bags of superphosphate plus one bag of muriate of potash into a spreader and then mixing them together.

In essence you have two granules of single super phosphate containing 8.8% P for each granule of muriate of potash containing 50% K – Refer Figure 11.1.

Figure 11.1  Diagrammatic representation of Super Potash 2 & 1 in granular form
Figure 11.1 Diagrammatic representation of Super Potash 2 & 1 in granular form

11.3.6 NP and NPK fertilisers

The terms NP fertiliser and NPK fertiliser are often used in conjunction with the term ‘mixture’ or ‘compound’. They refer to fertilisers that contain nitrogen and phosphorus (NP) or nitrogen, phosphorus and potassium (NPK). See Chapter 12 for more information on nitrogen and nitrogen fertilisers.

11.3.7 Granulated or pelleted fertilisers

Granulated fertiliser or pelleted fertiliser is a term applied to fertilisers that have been treated in such a way that they form granules to improve handling and spreading.

Granulation provides a number of advantages: it reduces the quantity of fine particles in a fertiliser, and it increases the flow and ease of spreading.

11.3.8 Organic fertilisers

The term organic fertiliser generally refers to fertilisers supplied or manufactured from animal or plant by-products. Examples include blood and bone, compost, chicken manure, dairy effluent and fishmeal products. There are, however, blurred definitions of what exactly is an organic fertiliser. This is because other fertilisers not from animal or plant by-products, can be classified as Australian Certified Organic, including potassium sulphate, reactive rock phosphate and seaweeds.

Nutrients contained within organic fertilisers will be released at varying rates depending on the complexity of how they are bound, their form and solubility within the fertiliser. Some nutrients can be released quite rapidly (e.g. potassium and nitrates) however, in general organic fertilisers tend to be slower releasing than mineral fertilisers. In other words, it takes time for the nutrients to become available in the soil for plants. They also usually contain fewer nutrients per kilogram than the inorganic fertilisers.

Organic fertilisers supply varying quantities of the major nutrients: nitrogen, phosphorus, potassium and sulphur, as well as some trace elements; and their composition can be quite variable. Generally, unless using very high application rates, the kg/ha of a plant available nutrient provided from organic fertilisers is low and may not keep up with crop removal. Hence conventional mineral fertilisers may also be required to balance soil nutrients and to maintain optimal soil fertility. They also contribute some organic carbon to the soil, which may improve the soil structure. Table 11.1 shows the averages and ranges of the major nutrients (N, P, and K) for a variety of animal manures.

Table 11.1  ‘Typical’ nutrient analyses (dry matter basis) for animal manures (average and ranges)  Note: Moisture content must be taken into account when costing the nutrients provided in organic fertilisers and when calculating the rate of the spread nutrients.
Table 11.1 ‘Typical’ nutrient analyses (dry matter basis) for animal manures (average and ranges) < br/> Note: Moisture content must be taken into account when costing the nutrients provided in organic fertilisers and when calculating the rate of the spread nutrients.

For more information on organic fertilisers:

There has been interest recently in the use of various humic substances in agriculture, namely humic acids and fulvic acids. Humic substances are the major part of humus. They are naturally occurring products found in soils and other places that are the result of the decomposition of plant and animal residues. Humic acids are generally used either in a liquid form when applied to plant foliage, or in a solid form when spread and incorporated into soil. Humic and fulvic acids are generally combined with other synthetic inputs to form a commercial product.

There are numerous advantages attributed to these two humic substances including:

  • Enhanced soil structure and fertility through the addition of vital organic matter in the soil;
  • Efficient transfer of fertiliser nutrients and micronutrients;
  • Increased microbial and enzyme activity in the soil;
  • Increased plant availability of nutrients like phosphorus;
  • Increased moisture holding capacity of soil; and
  • Increased cation exchange capacity within the soil

However caution is urged to try these products first in a “test strip” capacity (See Chapter 8.7 for information on setting up test strips).

11.3.9 Trace elements or micronutrients

Trace elements or micronutrients are the terms applied to the essential elements for plant growth and animal health that are required in only small quantities. Trace elements can be added to most fertilisers to meet particular needs. The most commonly added trace elements in eastern Australia are molybdenum, copper, zinc, boron, selenium, and cobalt. It is rare, however, for all these trace elements to be required at the same time, or to be added in one product. See Chapter 3.4 for more information on trace elements.

11.3.10 Slow-release fertilisers

In order to better synchronise the availability of nutrients to plant demand and, in doing so, increase nutrient use efficiency, slow-release fertilisers have been developed. These fertilisers have been produced in such a way that they are not readily water soluble. Treatment usually involves coating the fertiliser granules with a slowly soluble material, such as sulphur or wax. Because of the extra processes involved in coating the granule, these products are usually more costly than non-coated products. Examples of coated slow-release fertilisers include horticultural products, such as Osmocote.

Reactive rock phosphates are very slow release in that they dissolve slowly in acid soils to become available to plants naturally. Similarly, elemental sulphur must be converted to the plant-available sulphate sulphur form before it can be used by plants. Therefore, elemental sulphur is also considered a slow-release fertiliser compared to sulphate sulphur.

Fertilisers are now commercially available that modify or reduce the rate by which fertiliser nitrogen becomes plant available. Known as nitrification inhibitors, they have specific coatings or treatments that work by slowing the release of nutrients, or by delaying the conversion to less stable forms. The slower release of nitrogen during the nitrification process, and potentially greater nutrient use efficiency, is due to the inhibition of specific enzymes and nitrifying bacteria. By inhibiting these enzymes, more nitrogen is retained in the stable ammonium (NH4+) form. The effect of the inhibitors on specific nitrifying bacteria reduces the amount of the very soluble nitrate nitrogen which can be more readily lost through leaching and denitrification. For more information on the nitrification process and denitrification refer to Chapter 12.

11.3.11 Liquid fertilisers

Liquid fertilisers refer to nutrient solutions, suspensions and slurries and are usually sprayed onto pastures. According to the Dairying for Tomorrow Survey they are not widely used in the Australian dairy industry, apart from the spreading of dairy effluent (Dairy Australia, 2012). However, some nitrogen solutions are gaining popularity in northern Victoria, especially through fertigation under centre pivots.

11.3.12 Alternative fertilisers

The term alternative fertiliser refers to those products that fall outside the category of products generally known as fertilisers to the farming community.

Many products, making a wide range of beneficial claims, continually arrive on the market. When prices of conventional fertilisers rise, it is often tempting for some farmers to look towards alternatives. It is sometimes difficult to know whether alternative fertilisers will perform as claimed by the company. There are a number of checks that can be done to avoid costly mistakes, including the following:

  • Ask for the nutrient analysis, and check the analysis was conducted by a reputable testing laboratory.
  • Compare the product nutrient analysis, the form or plant availability of each nutrient, and the cost per kg of nutrients with other fertilisers – Refer to Section 11.4.1 and Chapter 14 to work out nutrient costs.
  • Check that nutrients contained in the product are required by the soil, plant or livestock.
  • Ask for the research to back the product claims. Question the credibility of the research – was it a simple side by side demonstration or a replicated trial? Where was the research done – Australia or overseas? Was it conducted by an independent organisation? Was the research peer reviewed? Is it only anecdotal observation?
  • Sometimes products may make claims which cannot be explained by their nutrient content or fertiliser value. In these cases, if the product works it would be due to some growth promotant effect and could not be directly compared with traditional fertilisers or manures. If you believe the products could be beneficial, but there is no existing product analysis or credible research to back the claims, reduce the risk by trialling the product with fertiliser test strips. Always include a nil strip and, if possible, include a standard product for comparison – Refer to Chapter 8.7 for details on setting up a fertiliser test strip.

Other alternative fertilisers include the various forms of manures, composts and biosolids. These have increased in popularity due to commercial fertiliser price rises and their contribution to soil health. It is important to weigh up the costs and benefits of alternative fertilisers in comparison to other products.

Biosolids, whilst being an attractive nutrient source, currently have to be incorporated into the soil within hours of application for legal and health reasons. This is obviously not feasible for pastures. In addition, there are concerns about substantial nutrient losses (nitrogen) and nutrient accumulations (trace elements and phosphorus) when this product is applied to the soil.

Manures and composts when applied to pastures will provide a range of nutrients (See Table 11.1) some being immediately available and others requiring decomposition before becoming plant available. The application of manures and composts to crops and pastures should not be on the basis of ‘’getting rid of a waste product” but applied in accordance with soil nutrient requirements (See Chapter 15, Nutrient Planning).