What is leaching
Leaching is a process that consists of the superficial washing of mineral salts into the deeper layers of the soil, mainly by the runoff of surface water. In this sense, leaching causes losses of nutrients from the soil, the main consequence of which is acidification.
There are some factors that intensify the erosion and leaching process, such as: the absence of vegetation cover, low levels of organic matter, high rainfall intensity at certain periods of the year and shallow soil depth.
Nutrients that undergo leaching
Certain nutrients are more easily leached into the soil because, due to their chemical properties, they have greater mobility throughout the soil profile.
Potassium
One of the nutrients that suffers the most leaching is Potassium (K+). When present in the soil solution, the nutrient can be lost through leaching according to the amount of water, the dose of the element applied, the texture of the soil and the cation exchange capacity (CEC) of the soil.
Potassium chloride (KCl), the main source of potassium used in Brazilian agriculture, is a salt highly soluble in water and, therefore, its main loss is through leaching. This loss can be minimized by using less soluble sources of potassium. Furthermore, like N, K is recommended to be applied in installments, in order to minimize losses.
Nitrogen
Nitrogen is absorbed by plants in the forms of nitrate (NO3-) and ammonium (NH4+), with nitrate being an anion that is more susceptible to leaching due to low chemical interaction with soil minerals. Therefore, fertilizers that contain this anion are more likely to be lost
The leaching of N resulting from organic matter occurs when plants have insufficient roots to absorb the N mineralized by nitrifying bacteria in the soil. Urea (CH4N2O), one of the widely used N sources, has high solubility and poor adsorption by colloids. As a result, it is subject to being lost through leaching.
Sulfur
Losses of Sulfur (S) in the form of sulfate (SO42-) are highly prevalent in soils affected by large amounts of rain, especially in cases where the soil has a low sulfur adsorption capacity. Furthermore, soil management has an influence on this process, in which liming and phosphating allow the displacement of this nutrient into the soil solution, which can cause the loss of the nutrient.
Boron, Calcium and Magnesium
In sandier soils, in conditions of high rainfall, this leads to low Boron availability due to leaching losses. In addition to Boron, Calcium and Magnesium are also lost through this process, which are introduced into the soil mainly through the liming process.
How to supplement leached nutrients
A parameter that has a direct influence on the nutrient leaching rate is the soil CEC. Therefore, having a soil with a good CEC is a measure to reduce nutrient losses through leaching. For a soil to have a high CEC, it is very important to use techniques that promote an increase in the soil's organic matter content. Furthermore, soils with a higher CEC retain more potassium in the solid phase and with an increase in soil pH, the retention of K and other cations in the solid phase increases, reducing losses through the leaching process.
