Secondary and micronutrients in plant nutrition and organic fertilisation

Organic fertilisation can significantly influence this availability, both directly—by supplying specific nutrients bound to the organic matrix—and indirectly, by positively affecting the physical and biological properties of the soil.

The main secondary nutrients are Calcium, Magnesium and Sulphur. The main micronutrients are Iron, Manganese, Zinc, Copper, Boron, Molybdenum and Chlorine.

Although required in limited quantities, these elements are fundamental to plant metabolism, and deficiencies can compromise growth, yield and quality.

Magnesium. It is the core of the chlorophyll molecule and therefore plays a direct role in photosynthesis. Without adequate Magnesium availability, plants cannot efficiently use light energy. By activating numerous enzymes, it is also central to energy metabolism.

Sulphur. It is required for the synthesis of sulphur-containing amino acids, proteins and enzymes. It plays a key role in vegetative growth and production quality. In many crops, it also contributes to the organoleptic and nutritional quality of the product.

Iron. It is involved in respiration, photosynthesis and electron transport processes. It is not part of chlorophyll, but is indispensable for its synthesis. Its deficiency is frequent in calcareous or high pH soils, where typical iron chlorosis occurs.

Manganese. It participates in numerous enzymatic reactions and is involved in photosynthesis and nitrogen metabolism. Its availability easily decreases in alkaline soils.

Zinc. It is essential for the synthesis of plant hormones, particularly auxins, and for shoot growth. It is also involved in leaf development and in the regulation of various enzymatic processes.

Copper. It is necessary for the proper functioning of many enzymes and for lignification processes. It contributes to tissue strength and stress response, but must be carefully managed to avoid accumulation in the soil.

Boron. It is essential for cell division, flowering, fruit set and sugar transport. It is one of the most delicate micronutrients to manage, as the threshold between deficiency and excess is very narrow.

Molybdenum. It is involved in Nitrogen metabolism, particularly in nitrate reduction. Although required in minimal quantities, it is crucial for the nutritional efficiency of many crops.

Chlorine. It participates in osmotic processes and stomatal function. It is less frequently mentioned than other micronutrients, but its physiological role remains important.

In calcareous or alkaline soils, Iron, Manganese, Zinc and Boron are often less available. In very acidic soils, on the other hand, some micronutrients may become excessively soluble: examples include Manganese and Zinc, which at low pH values can induce phytotoxicity phenomena in crops.

Bioavailability of secondary and micronutrients depending on soil pH

Among the most well-known antagonisms is that between Manganese and Iron: an excess of Manganese can drastically reduce the uptake of Iron and vice versa. This balance is crucial, as both elements are essential for photosynthetic processes.

The soil organic matter, particularly the humified fraction, plays a key role in this context. Secondary and micronutrients contained within it are released into the soil solution over time as a result of mineralisation. This slow and gradual release prevents losses—mainly through leaching into deeper soil layers—of nutrients not absorbed by plants.

Moreover, humic and fulvic acids chelate secondary and micronutrients, facilitating their transport towards plant roots.

Finally, an adequate organic matter content promotes the vitality of the soil microbiota, which—through the production of organic acids and enzymes—can **locally modify the pH of the **rizosphere (the zone surrounding the root), facilitating the uptake of micronutrients even in soils where their availability would theoretically be limited.

Fumier Sulfer derives from the intimate and homogeneous mixture of humified manure, partially hydrolysed animal proteins, micronised sulphur and ferrous sulphate heptahydrate. In addition to the characteristics already mentioned (Fumier Fer) regarding Iron and Sulphur, the role of micronised Sulphur is added. Fumier Sulfer is the ideal organic fertiliser for all herbaceous and tree crops requiring Iron and Sulphur.

Fumier Cars 70-30 derives from the intimate and homogeneous mixture of humified manures with vegetable proteins and dried molasses residue. The raw materials are mixed and cold-pelletised to best preserve the microbiological characteristics of the product. Fumier Cars 70-30 is an ideal fertiliser for basal fertilisation of all crops, as the properties of humified manure are combined with the supply of vegetable proteins from oilseed cakes. Humified manure, rich in humic and fulvic acids, promotes optimal soil microbiological activity and better use of nutrients in the soil thanks to the formation of organo-mineral complexes, which protect nutrients from negative phenomena such as leaching and retrogradation, making them available to plants.