Manganese is an indispensable trace element for crop growth. Known as the photosynthesis booster and metabolic activator, it dominates the primary reaction of photosynthesis and activates hundreds of key metabolic enzymes in plants. Manganese deficiency directly leads to premature leaf senescence, yield reduction and frequent disease occurrence.
I. Manganese: Core Booster for Photosynthesis
Manganese constitutes an essential part of the water-splitting complex in Photosystem II of chloroplasts. It is the only nutrient element directly involved in water photolysis and oxygen release among all crops.
It completes the first step of photosynthesis: decomposing water molecules under light to release oxygen and generate photosynthetic energy simultaneously. Photosynthesis cannot initiate without manganese.
It stabilizes chloroplast structure: maintains the integrity of chloroplast membranes and delays chlorophyll degradation. Manganese deficiency causes chloroplast damage and rapid loss of chlorophyll.
It improves light energy conversion efficiency: sufficient manganese can markedly accelerate the synthesis of sugar and starch, rendering leaves thick, dark green and vigorous.
Manganese has extremely low mobility inside plants. Manganese stored in mature leaves cannot be transported to newly growing tissues, so manganese deficiency symptoms usually first emerge on upper and middle new leaves. The typical manifestation is green leaf veins with interveinal chlorosis in mesophyll, accompanied by tiny brown necrotic spots within yellowed areas. This is the most vital feature to distinguish manganese deficiency from iron deficiency and magnesium deficiency.
II. Versatile Metabolic Activator Regulating Physiological Activities of Whole Plants
Manganese acts as a specific activating cofactor for more than 30 key enzymes, covering respiration, nitrogen metabolism, antioxidation and cell wall synthesis.
Activate enzymes related to nitrogen metabolism
It regulates the activity of nitrate reductase and accelerates the conversion of nitrogen fertilizer into amino acids and proteins. Under manganese deficiency, crops cannot absorb and utilize nitrogen even with heavy nitrogen application, resulting in weak plants and poor flower bud differentiation.
Build antioxidant defense system for crops
It activates superoxide dismutase, peroxidase and polyphenol oxidase to eliminate harmful free radicals produced under high temperature, drought and phytotoxicity, slow down leaf aging and abscission, and enhance stress resistance.
Strengthen cell walls and boost disease resistance
It participates in the synthesis of lignin and phenolic compounds to thicken cell walls and block the invasion of fungi and bacteria. Supplementing manganese for wheat, rice and fruit trees can significantly lower the incidence of rust, brown spot and leaf spot diseases.
Balance endogenous hormones
It takes part in the synthesis and transportation of auxin and cytokinin, promoting bud germination and root elongation. Manganese deficiency at seedling stage causes uneven emergence, stunted, yellow and weak seedlings.
III. Primary Causes of Manganese Deficiency in Soil
Soil alkalinity is the leading cause
When soil pH＞7.0 (calcareous land, saline-alkali greenhouses, plots applied with quicklime for a long time), soluble divalent manganese is rapidly immobilized into unavailable trivalent manganese which cannot be absorbed by roots. Yellow leaves caused by manganese deficiency commonly occur in northern orchards and vegetable greenhouses.
Low soil organic matter content
Organic matter can chelate manganese ions and improve manganese availability. Sandy barren soil contains little organic matter, and manganese is prone to leaching and loss.
Element antagonism inhibits absorption
Long-term excessive application of lime, calcium fertilizer and phosphate fertilizer will cause manganese to precipitate after combination with calcium and phosphorus, blocking root absorption.
IV. Practical Guidelines for Rational Manganese Fertilization
- Optimal Periods for Manganese Supplement Seedling stage and new shoot sprouting stage: strengthen seedlings rapidly and prevent early yellow leaves; Vigorous photosynthesis stage (tillering, fruit setting and fruit expansion stages): guarantee nutrient production; Carry out emergency foliar treatment once slight interveinal chlorosis and spots appear on leaves.
- Two Manganese Application Methods
- Soil base application / fertigation Apply manganese sulfate at 1–2 kilograms per mu together with organic fertilizer to reduce soil immobilization. Suitable for base fertilizer and root irrigation.
- Foliar spraying (fastest effect) Sugar alcohol chelated manganese and amino acid manganese, diluted to 0.1%–0.2% for foliar spray, once every 7–10 days for continuous 2 applications, to rapidly eliminate yellow spots on leaves.
- Application Taboos Manganese fertilizer cannot be mixed with quicklime, high-concentration calcium fertilizer and high-phosphate fertilizer. Strictly control application concentration; excessive manganese triggers manganese toxicity, featuring extensive scorched spots on leaves and blackened decayed roots. Acidic red soil generally contains abundant manganese; frequent manganese supplement is not recommended to avoid toxicity.
V. Typical Manganese Deficiency Symptoms of Different Crops
Dicotyledons (tomato, fruit trees, sugar beet, soybean): reticular interveinal chlorosis on new leaves scattered with round brown spots; spots may perforate in severe cases.
Gramineous crops (wheat, rice, corn): streaky chlorotic grey spots on leaves, commonly known as grey spot disease, less tillers and shrunken grains.
General hazards: fewer flowers and fruits, small fruit size, uneven pigmentation, deteriorated quality and premature leaf senescence and abscission of plants.
