The Chemical Engineering Department of the UCLM has developed a study on the control of soil salinity through the use of saline correctors. The objectives have been to evaluate if the addition of specific agrochemicals improves the removal of excess salts in soils, how these influence the movement of the ions that cause saline stress, and what is the performance of each agrochemical in the soil.
The world has an estimated 45 million hectares of irrigated land with salinity problems and 1.5 million hectares become unproductive each year as a result of high salt concentrations.
Salinity, which is responsible for the increase of the soil's osmotic potential, and the specific toxicity caused by some ions, are limiting factors for agricultural productivity, affecting the plant in several ways. These effects have an impact on the growth, development, survival, germination and vigor of the plant. In short, the crop yield decreases.
Therefore, it is necessary to apply efficient and low-cost treatment strategies to reduce the toxicity of salt in soils. The lixiviation of sodium from the root area is one of the most common and effective methods. The Chemical Engineering Department of the UCLM has evaluated several commercial products. The goal is to determine the influence of each of them on the different ions present in the soil as a result of irrigation with low quality water and fertilization with standard nutrient solutions. It is trying to simulate, in the most precise way possible, a real situation of a soil in fertirrigation with low quality water.
Material and methods
Soil cleaning tests have been carried out in pots with 40 kg of agricultural soil, to which the bottom was drilled for the collection of leachate in a closed container in order to avoid losses due to evaporation.
Image 1. Test setup.
The compositions of each commercial product tested are detailed below:
9% CaO p/p complexed with low molecular weight carboxylic acids.
Organcalcic complex (10% CaO p/v).
12% CaO p/p amidic nitrogen 9% p/p
7.5% CaO p/p, 0.5% MgO p/p with organic acids.
In order to ensure an equal leachate flow, each pot was watered for 2 weeks before the start of the test with 0.5 l of saline a day, and 1 l during the last week. It was irrigated with a standard nutrient solution, to which a high amount of sodium chloride was added.
In each test, the pH, conductivity and ion concentration (Cl-, Na+, NO3-, SO42-, Ca2+, Mg2+, PO43-) were monitored over time in the leached stream (daily sample) and in the soil. The leachate measurement provides information about the free quantity of ions that are mobilized together with the water passing through the pot by gravity, while the post mortem measurement test reveals the amount of ions retained in the soil.
pH: The pH of the leached volumes was measured; the differences were not significant.
Electrical conductivity Lm (mS/cm): Based on the data obtained, the addition of a product for the release of ions had a positive impact, especially noteworthy in the case of Product 1.
Ions in the leachate: The amount of sodium present in the soil is one of the most important parameters when measuring its quality. Finding out how much has been removed is one of the most important results of this study. The amounts of sodium removed (in mg/l per kilogram) are shown below.
Although the leachate flow of products 1 and 3 was lower than that of the control, these managed to free more sodium from the soil.
The amount of ions collected in the leachate was also measured. See table below:
At the end of the experiment, the Chemical Engineering Department of the UCLM revealed that Product 1 was Carbosoil, from Carbotecnia. This product shows the following benefits with respect to the rest of the products and to lixiviation with water alone.
• Lower plugging of soil porosity, as a result of its formulation without high molecular weight substances (organic matter, lignosulfonates, etc.). Pore plugging causes salts to rise by capillarity, therefore affecting the plant.
• Carbosoil has a selective lixiviation effect, removing sodium and chlorine to a greater extent than other products, and leaching less nitrogen, potassium, magnesium, etc. than the rest of the products.
Regarding the questions raised, with the tests already carried out, the following conclusions have been reached:
Does the addition of specific agrochemicals improve the cleaning of excess salts in soils?
All products reduce the lixiviation rate (plugging of soil pores), achieving greater evaporation.
Products 1 (Carbosoil) and 3 are the ones that have the lower plugging effect.
How do agrochemicals influence the movement of ions that cause saline stress?
Product 1 (Carbosoil) to a greater extent, and 3 to a lower one, contribute to facilitating the mobility of ions, despite the lower mobility of water by gravity with respect to the control test.
Products 2 and 4 do not seem to have any kind of influence outside the very low leachate flow rate.
What is the performance/capacity of each agrochemical in the lixiviation of salts?
Product 1 (Carbosoil) has a positive effect on the extraction of sodium, sulfate and chloride ions. Also worth noting is the containment in the loss of nitrates as a result of the soil's hydraulic conductivity.
Product 3 has a similar, but less significant performance.
Carbosoil, the product marketed by Carbotecnia, is the one with the most optimal characteristics as a soil improver when it comes to removing harmful salts. As an update of the work of Puertas Tijeras, M., Fernández Rodríguez E.J. and Camacho Ferre F, the excellent development of Carbosoil's formulation has been demonstrated.