The Minor Nutrients Group
With the exception of Boron, which is a transitional element or semi-metal with a neutral ionic charge, the remaining four elements (Iron, Manganese, Copper, Zinc,) in the 3-4-5 Dynamic Plant Nutrient Model are all metallic cations. Whilst the supply of these metallic cations is actually maintained by the cation exchange capacity so technically an aspect within the clay mineralogy and therefore part of the Basic group; the total occupancy of the cation exchange by all these metallic elements in the minor nutrients group is less than 0.1%.
Furthermore all five are essential minor nutrients that are used in a regulatory capacity in the plant as opposed to the metabolic function of the four major cations. Thus as cations they are technically maintained by the cation exchange capacity. However they perform a very different function within the plant and collectively occupy less than 0.1% of the available exchange sites of the Cation exchange capacity. Thus insignificant in the functioning of the cation exchange they are considered separately and are better managed through direct measurement or in response to evidence of deficiency in the plant.
Thus it is the five micro nutrients below that make up the minor nutrients group of the 3-4-5 Dynamic Nutrient Model. These five are the most likely to be found wanting out of the remain 12 minor nutrients. Thus the five minor nutrients below together with the the three biotic and four basic nutrients collectively make up the 12 nutrients of the 3-4-5 Dynamic Nutrient Model.
Physiological Function: Boron is an essential plant minor nutrient that is involved in cell wall structure, membrane function and metabolic activities. In particular Boron functions to regulate sugar and carbohydrate production and subsequent translocation within the plant. Boron further plays a significant role in nitrogen metabolism and assimilation and is essential for nitrogen fixation in legumes. Boron has also been implicated in counteracting toxic effects of aluminium on root growth of dicotyle-donous plants (Blevins & Lukaszewski 1998)
Origin and fate or Boron Most soil Boron originates from the weathering of primary minerals within the parent soil. Subsequent uptake from crop plants and leaching into ground waters, particularly in areas of high rainfall or on light textured (sandy) soils make Boron the most likely minor nutrient to be deficient. Boron deficiency is particularly prevalent in the humid tropics however there is some evidence that the effects may well be less acute in coastal temperate zones where Boron inputs from precipitation may be sufficient to offset losses. For minimum and maximum Soil concentrations a good resource can be found at Spectrum Analytic and another
nice article can be found here at the science in farming library – Boron
Deficiency symptoms and treatment in plants The various functions Boron plays in plant metabolism and the relative significance those functions have to different plant species causes Boron deficiency to manifest in a variety of ways depending on the specific crop: a good wikipedia article can be found here
Physiological Function: Although Iron fulfils several metabolic functions it is a minor nutrient that is chiefly associated with chlorophyll development and function.
Origin and fate of Iron Most soils contain sufficient Iron for plant growth however Iron deficiency can occur at or above pH6.5 as a consequence of lime chlorosis or under permanent waterlogged conditions as a consequence of oxygen reduction (reducing Fe3+ to Fe2+). The condition is characterised by the presence of blue grey streaks within the soil profile which under severe conditions can turn the whole profile slate blue. science in farming library – Iron
Deficiency symptoms and treatment in plants: Lime chlorosis normally affects specific acid loving plants and is generally a problem associated more with ornamentals. A nice pdf from the University of Arizona’s Collage of Agriculture and Life Sciences on treatment of deficiencies or excesses in the home yard can be found here.
Physiological Function: Manganese plays an important role in regulating photosynthesis within the plant.
Origin and fate of Manganese: Manganese originates from the weathering of primary minerals in the soil and whilst it can become deficient on some acidic organic soils where it is leached it is more commonly deficient on alkaline soils where increasing pH depresses Manganese solubility. A nice pdf from incitecpiot.com (australia): manganese fact sheet
Deficiency symptoms and treatment in plants Manganese deficiency manifests first as a yellowing of the leaves followed by interveinal chlorosis and brown necrotic spots leading to leaf drop. It can be corrected by additions on deficent acid soils but where the deficiency is a a consequence of high pH it is best treated through a foliar application. Again a good clear fact sheet from Spectrum Analytics – Manganese
Physiological Function: Copper is another one of those minor nutrients that plays a role in enhancing a variety of metabolic and physiological functions within the plant. In many respects copper whilst essential in the nutrition of plants is perhaps more important for the nutrition of the animals and humans that consume the plants than it is for the plant itself. An excellent paper on Copper in Plant, Animal and Human Nutrition can be found on the site of the Western Australian company Amgrow Speciality and another from the Brazilian Journal of Plant Physiology
Origin and fate of Copper: Copper originates from the weathering of primary minerals in the soil and in more recent years significant inputs have come from pollution and fertiliser and pesticide use. Copper reserves in most soils are sufficient however it is a divalent cation and so prone to being locked out by high concentrations of other elements, pH and organic matter complexes.
Deficiency symptoms and treatment in plants Copper deficiency manifests as chlorosis and distorted growth in young leaves leading to die-back. Symptoms include wilting, lodging and high tillering in cereals. In dicots leaves may first become bluish and plants stunted with poor fruit set. here is a nice page from the University of Minnesota on copper and crop production and a PhD Dissertation on the factors affecting copper mobility from the Virginia Polytechnic Institute and State University as well as another excellent data sheet from Spectrum Analytics – Copper
Physiological Function: Zinc is another essential minor nutrient that performs a variety physiological functions from the structural and functional integrity cell membranes to the facilitation of protein synthesis and gene expression. The role of zinc to life , a nice pdf is available from the journal of environmental pathology, toxicology and oncology.
Origin and fate of Zinc: Zinc originates as with nearly all the trace elements from the weathering of primary minerals in the parent soil. An excellent book which is free: Zinc in Soils and Crop Nutrition: and written by a former lecturer of mine at the University of Reading: Prof Brian Alloway (who at that time was the head of the Soil Science Dept) is available from several sources Zinc in Soils and Crop Nutrition: Well done Brian for making this work free!
Deficiency symptoms and treatment in plants It is likely that Prof Alloway’s book above is all you need but for a shorter more concise fact sheet: Spectrum Analytics -Zinc
another good resource for identifying nutrient deficiencies in plants can be found at plant physiology on line
It is rare, with the exception of Aluminium, and occasionally Chlorine in glass house soils, for the remaining 7 elements needed by plants to be significant in terms of availability or function within the system. They are ‘incidental’ and whilst important physiologically and covered in the next page they can largely be ignored in terms of fertility. Only one other ‘nutrient’ of importance remains but unlike the others it is not an element but an organic compound; Ammonia (NH4)
In addition to these five elements a plant also requires a further seven elements (the incidental), bringing the total number of elements supplied and maintained by the soil matrix to nineteen. However most are required in such small amounts and abound sufficiently in the soil environment to be adequately supplied without intervention.
The incidental and accidental nutrients. The seven other essential elements needed for plant and the two accidental elements needed for animal nutrition that in general are capable of taking care of themselves.
Free Cultural Works (CC-BY-NC-SA) Malcolm McEwen 2011