Requirements in Plants
Australian Turfgrass Management Volume 2.3 (June - July 2000)
Plant growth depends on access to a supply of water, carbon dioxide, oxygen, photosynthetically active radiation (a component of "sunlight"), and a range of mineral nutrients.
Brief history of fertilisers
Improvements in knowledge on plant physiology towards the end of the 19th century resulted in the development of fertilisers such as potash and superphosphate to improve crop yields. Inorganic nitrogen fertilisers were later developed and used widely in European agriculture. However, farmers in Australia found that crops on some soils remained unproductive despite additions of nitrogen, phosphorus, and potassium fertilisers. Plants showed symptoms of tissue damage, and microbiologists from Europe suggested that a disease organism must be involved. A group of scientists from Adelaide identified the cause as manganese deficiency. This discovery lead to research world-wide on the use of many other elements to correct crop disorders. This in turn gave rise to the development of fertilisers to supply both "macronutrients" and "micronutrients".
Essential macro- and micro-nutrients for plants
Macronutrient is the term given to those elements required in relatively high concentrations in plant tissues. Micronutrient is the term given to elements required only in small amounts. The essential macro- and micro-nutrients found in plant tissues, and average tissue concentrations, are given in Table 1.
Table 1. List of essential nutrients for plant growth. The average concentration of each element found in dried shoot tissues from plants supplied with adequate nutrients is also given. Taken from Marschner (1995) in Mineral Nutrition of Higher Plants, Academic Press. Tissue concentrations can vary widely depending on plant species and environmental conditions, so these data should not be used as standards for tissue tests.
Macronutrients (% by weight)
Micronutrients (ppm, or mg/kg)
The term "essential nutrient" is used to describe elements that are:
(i) necessary for a plant to complete its life cycle, and
(ii) perform a function which can not be replaced by another element.
The elements are essential for plant life since they are either:
(i) Directly involved in plant metabolism; for example as a component of an essential plant constituent (e.g. nitrogen in amino acids and proteins).
(ii) Required for a distinct metabolic step (e.g. manganese is a co-factor in several enzyme reactions).
Some elements are termed "beneficial" nutrients. These are not essential since plants can complete their life cycle without them. One example is silicon, which can stimulate growth when supplied to some (but not all) species.
Not all elements are essential or beneficial to plant growth; some can be toxic. For example, aluminium can be highly toxic in acidic soils and sodium can be toxic when at high concentrations (e.g. in saline soils or salt-affected irrigation water). A typical dose-response curve for plant growth when supplied with any mineral element is shown in figure 1.
Figure 1. Graph showing the generalised relationship between rate of nutrient supply and plant growth. The three stages of the relationship (deficient, adequate, and toxic) are discussed in the text.
Response of plant growth to nutrient supply
The response curve of plant growth to nutrient supply has three defined regions (figure 1). In the deficient range, plant growth increases with additional nutrient supply. In the adequate range, growth reaches a maximum and remains unaffected by the supply of additional nutrient. In the toxic range, plant growth declines with increasing nutrient supply.
In turf culture, like in other plant management systems, the desired nutrient supply is achieved by fertiliser applications. Efficient use of the applied nutrients should be one objective of turf managers, since this minimises nutrient losses and subsequent impacts on the environment. Information on nutrient availability in the soil and on the nutrient status of the plants, via soil and tissue testing, can aid management decisions and improve efficiency of fertiliser use.
Diagnosis of nutrient disorders
The occurrence of visible symptoms usually only applies in cases of severe deficiency or toxicity. The growth rate of any plant would have decreased substantially prior to the development of symptoms. Furthermore, diagnosis of nutrient disorders in field-grown plants based on visible symptoms can be complicated, due to possible interactions of multiple factors (e.g. other deficiencies, diseases and damage from other sources). Any diagnosis is aided by information on fertiliser history, soil pH, weather conditions, and recent management of the area.
The transport physiology of the nutrient in question will determine the tissue in which the symptoms appear. Deficiency symptoms for "phloem mobile" elements (e.g. nitrogen) appear in the older leaves since the elements are re-translocated to the new growth; whereas for "phloem immobile" elements (e.g. calcium) symptoms develop in the young leaves. In some cases (e.g. iron deficiency; see plate 1) the symptoms are so obvious that a management recommendation (e.g. foliar spray of an iron source) can be given in a short time frame. In many cases soil and plant tissue tests will be required.
Soil and plant analyses as management tools
Soil analyses will provide information on the potential availability of nutrients for uptake by plant roots. Plant tissue analyses reflect the actual nutritional status of a plant. The two approaches are used in combination to provide information on nutrient status in a plant-soil system.
The use of chemical analyses of plant materials for diagnostic purposes requires strict standardisation of sampling procedures and the availability of suitable reference data for the species of interest. The sampling procedure required depends on the reason the sample is being taken (Table 2), and the appropriate tissue to be sampled will depend on whether, or not, the target nutrient(s) are phloem mobile (e.g. sample young or old leaves). Steps must be taken to avoid potential contamination from several sources. Despite these complications plant tissue analyses, when used appropriately, are a valuable tool for turf managers.
Plate 1. Photograph showing symptoms of iron deficiency in Kikuyu growing on an alkali coastal sand in Western Australia. The leaf chlorosis was corrected by a subsequent foliar application of soluble iron. Photograph courtesy of Ken Johnston, Sports Turf Technology, Perth, WA.
Table 2. Summary of common reasons for taking plant tissue samples for elemental analyses. Modified from Robinson (1993) in Australian Journal of Experimental Agriculture 33:1007-1014.
|Reason||Sampling options||Comparisons to be made|
|Diagnosis|| Defined tissue
Good" and "poor" plants
Against each other
|Monitoring||Defined tissue and time
(seasonal or yearly)
Previous data to see trends over time
Dr. Tim Colmer is a lecturer in Plant Sciences at the University of Western Australia. Dr. Colmer co-ordinates the Turfgrass Research at UWA, a program in collaboration with industry