The role of organic matter in managing saline soils

It is certainly not only agricultural soils near coastal areas that present salinity issues. Once associated almost exclusively with inherently limiting soils due to chemical composition or location, this problem has now seen a sharp increase in prevalence, driven by intensive farming practices and climate change, particularly high temperatures and irregular rainfall.

A soil is defined as saline when it contains high concentrations of soluble salts—particularly chlorides, bicarbonates, and sulfates of sodium, potassium, calcium, and magnesium—which result in an electrical conductivity greater than 4 dS/m, the threshold considered for saline soils.

Increasing electrical conductivity leads to increasingly severe crop problems.

Excess mineral elements forming salts in the substrate depend on multiple environmental and pedological factors, including local climate characteristics, territorial morphology, geological nature of the bedrock, and the chemical composition of groundwater and irrigation water.

Salinization is a progressive soil degradation process that severely compromises fertility and drastically limits productive potential. Plants rooted in saline soils experience osmotic stress and often show nutritional imbalances due to difficulty absorbing essential nutrients, as well as phytotoxicity phenomena.

There are two main types of salinization: primary, caused by natural factors, and secondary, induced by human activity.

Primary salinization occurs mainly in ecosystems with very low rainfall, where available water is insufficient to leach naturally occurring salt accumulations in the soil profile. In these conditions, salts progressively accumulate in upper horizons instead of being washed deeper by rainwater. When salt levels become unsustainable—beyond what irrigation water can remove—a vicious cycle begins. Irrigation inputs, instead of solving the problem, intensify salt concentration through evaporation: as water evaporates, salts migrate to the surface and remain there.

Continuous application of irrigation water containing even minimal saline substances can, over the medium to long term, significantly increase soil salinity. This is the main cause of secondary salinization, along with the excessive and irrational use of mineral fertilizers.

The problem is even more severe in poorly permeable soils, where percolation water struggles to penetrate deeply, causing the accumulation of large volumes of saline water in root zones.

Among the most characteristic symptoms in crops grown on saline soils are irregular and uneven growth, with evident loss of vegetative vigor.  Agricultural species exhibit different tolerance levels to salinity.

Among the most sensitive are rice, various stone fruits, and maize; among the most tolerant are leaf beet, barley, and spinach.

Visually, soils often show salinity through whitish surface deposits or crystalline formations.
Soil salinity can be measured both in the field, using portable instruments (conductivity meters), and in the laboratory with more precise equipment. Recently, several methods have been developed to detect soil salinity and its spatial variability using proximal and remote sensing techniques.

The organic component of soil plays an essential role in managing saline issues. Increasing organic matter content significantly improves soil structure, promoting optimal water balance and drainage of excess saline solutions. In well-structured soils, surface evaporation is also reduced, limiting the capillary rise of salts from deeper horizons.

Moreover, organic matter contributes to increasing cation exchange capacity, allowing the soil to retain more essential nutrients during rainfall or irrigation, while leaching carries sodium ions—poorly retained by organic matter—downward.

Adequate organic matter levels also enhance soil microbiological activity, particularly that of rhizosphere microorganisms that improve nutrient availability for plants, as well as halophilic microorganisms, such as proteobacteria and actinomycetes, which remove chlorine and sodium from the circulating solution because they require high concentrations of these elements to thrive.

In saline soils, it is essential not only to avoid cultivating species highly sensitive to salinity but also to select more tolerant varieties of those that can grow in such conditions.

Beyond varietal choice, the two key cultural practices are fertilization and irrigation.
It is necessary to limit the use of mineral fertilizers, especially those with a high salinity index. When used, doses should be split, to avoid peaks of saline concentration in the soil.

Fertigation, when properly applied, allows nutrients to be distributed evenly and in a controlled manner, reducing the risk of localized accumulation. However, constant monitoring of both irrigation water quality and soil electrical conductivity is essential to prevent negative effects.

Organic and organo-mineral fertilization should be preferred, given the beneficial effect of organic matter on saline soils. The humification rate of the organic matrix in these products is a key factor, due to the chelating action of humic and fulvic acids on nutrients, which is fundamental to counter nutrient loss during leaching irrigations.

Finally, do not underestimate the usefulness of fertilizers inoculated with beneficial microorganisms, particularly PGPR, mycorrhizal fungi, and nitrogen-fixing bacteria.

Fertilsoil is a mycorrhizal fungi inoculum designed to improve soil microbial fertility. Made with highly humified organic matrices, it contains a specific microbial consortium selected from fertile cultivated soils.

Its primary function is to enhance soil fertility by introducing microorganisms with specific activities such as nitrogen fixation, phosphorus solubilization, siderophore production, and indoleacetic acid production. Thanks to these microorganisms, the distributed organic matter, and naturally supplied humic acids, positive effects occur on the soil microbiota, consequently increasing biological fertility and improving crop performance.

Fumier Sulfer results from the intimate and homogeneous mixture of humified manure, partially hydrolyzed animal proteins, micronized sulfur, and ferrous sulfate heptahydrate. The humic acids in humified manure bind, through carboxylic and phenolic bonds, to bivalent iron (Fe++) forming iron humates.

Natural chelation then makes iron available through the complex organic matter cycle. Fumier Sulfer is the ideal fertilizer for all crops demanding iron and sulfur, such as vegetables (spinach, beet, and lettuce) and ornamental plants, and is also excellent for fruit trees like kiwi, cherry, and vine. The presence of sulfur, in addition to acidifying the soil, provides an important supply of this meso-element, improving plant development and crop quality (cereals, vegetables, and vines). Finally, its high sulfur and ferrous sulfate content promotes the formation of sodium sulfate in sodic soils, which is then leached by rain or irrigation, exerting an ameliorative effect on these limiting soils.