Manganese (Mn) is one of the 17 elements essential for plant growth and reproduction. It is needed in only small quantities by plants, but like other micronutrients, Mn is ultimately as critical to plant growth as are the major nutrients. Manganese is a micronutrient and is needed in only small quantities by crop plants. However, it is critical to growth as are the other nutrients. Manganese is an important plant micronutrient and is required by plants in the second greatest quantity compared to iron. Manganese is taken up by plants in the Mn2+ form, and in organically complexed forms.
Despite the importance of Mn for photosynthesis and other microbial processes, the physiological relevance of Mn uptake and compartmentation in coffee Agroforestry plants has been poorly researched.
Function of Manganese
Plants require manganese for a variety of biological systems including nitrogen assimilation, respiration and photosynthesis.
Manganese is also involved in pollen germination, pollen tube growth, and root cell elongation.
Participates in chlorophyll production
Activates enzymes, such as the nitrate-reducing enzyme and carbohydrate metabolism enzymes
Manganese is critical for synthesizing fatty acids. the regulation of carbohydrate metabolism(Starch Production) and the energy budget.
Manganese provides a strong immunity build up to fight soil pathogens.
The synthesis of lignin, which adds strength and stiffness to cell walls, is dependent Manganese.
An adequate supply of manganese is required to decrease nitrates within the plants.
Manganese also enhances the growth of the secondary roots and elongates cells to increase plant growth.
Manganese functions mostly as an activator in enzyme systems, but it is also a constituent of certain enzymes.
Influence of Soil Type
The Earth’s crust is about 0.11 percent Mn. Total Mn in soils generally ranges from about 20 to 3,000 ppm (0.002 to 0.30 percent), but only a fraction of this total is plant available. The reactions of manganese in soil are complex. The two major factors that affect manganese availability are pH and redox conditions.
Review of literature in peer reviewed journals suggest that Mn deficiency is a serious, widespread plant nutritional disorder in dry, well-aerated, neutral, or well drained and calcareous soils, as well as in soils containing high amounts of organic matter, where bio-availability of Mn can decrease far below the level that is required for normal plant growth By contrast, Mn toxicity occurs on poorly drained and acidic soils in which high amounts of Mn are rendered available. Consequently, plants have evolved mechanisms to tightly regulate Mn uptake, trafficking, and storage (Santiago et al. ) Other factors include microbial activity, soil temperature, and seasonal variations affect its availability to plants.
Soil moisture – Dry soil conditions also decrease manganese availability. On the other hand, manganese availability increases in waterlogged soils.
Microorganisms – Redox reactions carried out by microorganisms greatly affect manganese availability to plants.
Soil temperature – Higher soil temperature increases manganese availability, as manganese is reduced to the Mn2+ soluble form.
Influence of pH
Plant-available Mn increases as soil pH decreases, so deficiencies are more likely to occur in alkaline soils.
Mn deficiency can be a serious plant nutritional disorder in soils with high pH.
Mn deficiency can occur in soils subjected to heavy lime application.
Mn deficiency is also prominent in soils subjected to too much iron .
If soil pH is too low, less than 5, Mn can be toxic to sensitive crops.
Influence of Organic Matter
Soils rich in organic matter ( 6%) and with a Ph value of 6.5 may be deficient in manganese. As the organic matter content increases, the amount of exchangeable manganese decreases due to the increased formation of organic matter and manganese complexes.
Mn Deficiency
It is similar to iron in many ways, and manganese deficiency or toxicity is often mistaken or ion deficiency or toxicity. The normal concentration range of Mn in plants is typically from 20 to 300 ppm. When the Mn concentration falls below 15 to 20 ppm, deficiency often occurs.
Symptoms of Manganese Deficiency
Manganese, like many other micronutrients, is immobile in plants. This is an important point because it means that deficiency symptoms will first appear on younger leaves since the plant cannot easily scavenge Mn from older tissue. Manganese deficiency symptoms, which often look like those of iron deficiency, appear as interveinal chlorosis (yellow leaves with green veins) on the young leaves. A manganese deficiency in plants often results in chlorotic spots around the veins in mid and new leaves due to the negative impact of chloroplast development.
The major difference is that as manganese deficiency progresses, tan areas develop between the veins while iron deficiency progresses toward an almost white appearance in the leaves. With severe deficiency, plant growth may also be reduced and stunted.
Correcting Manganese Deficiency
For effective root absorption of manganese, the pH range should be between 6.0 and 7.0.
Use manganese sulfate in the prescribed dosage.
What fertilizer is high in manganese?
Manganese sulfate (MnSO4) is the most common of the Mn fertilizer sources. It is highly water soluble and suited for soil or foliar application. There are several other Mn fertilizer sources including chelates, chlorides, oxides, and oxysulfates .
Table 2. Manganese fertilizer sources, formulas and Mn content.
| SOURCE | CHEMICAL FORMULA | Mn CONTENT % |
| Manganese Sulfate | MnSO4·3H2O | 26-28
|
| Manganese Chloride | MnCl2 | 17 |
| Manganese Carbonate | MnCO3 | 31 |
| Manganese Oxide | MnO2 | 63
|
| Manganous Oxide | MnO | 41-68 |
| Manganese Chelate | MnEDTA | 12 |
| Manganese Frits | – | 10-25
|
Conclusion
Manganese is one of the main micronutrients, which has an important role in plants as a component of enzymes involved in photosynthesis and other processes. Manganese deficiency results in reduced crop yields and quality, mainly due to impairment of the photosynthesis process and synthesis of starch. More research is needed to understand the physiological implications of the role of manganese inside the coffee Agroforestry model.
References
Anand T Pereira and Geeta N Pereira. 2009. Shade Grown Ecofriendly Indian Coffee. Volume-1.
Anand Titus Pereira & Gowda. T.K.S. 1991. Occurrence and distribution of hydrogen-dependent chemolithotrophic nitrogen-fixing bacteria in the endo rhizosphere of wetland rice varieties grown under different Agro-climatic Regions of Karnataka. (Eds. Dutta. S. K. and Charles Sloger. U.S.A.) In Biological Nitrogen Fixation Associated with Rice Production. Oxford and I.B.H. Publishing. Co. Pvt. Ltd. India.
Subba Rao. N. S. 1998. Soil Microorganisms And Plant Growth. Oxford and IBH Publishing Co.
Bopanna, P.T. 2011.The Romance of Indian Coffee. Prism Books ltd.
Brouder, S. et al. 2003. Purdue University Cooperative Extension Service. Agronomy Guide AY-276-W.
Role of Manganese in Plant Culture.