Soil tillage effects on monovalent cations (Na+ and K+) in vertisols soil solution

Potassium is an essential macronutrient for plants; it is characterized by increased photosynthetic activity by ensuring a better utilization of light energy, also acts as a regulator of cell osmotic pressure, decreasing transpiration and helping to maintain cell turgidity. However, the sodium is not an essential element for plants, although it is beneficial to certain crops, in some instances can replace the potassium and osmotic regulation making and turgidity of the cells, this effect is greatest when the supply of potassium is deficient (Wild, 1992). Both elements, in periods of aridity, delayed the wilting of plants to maintain cellular osmotic potential and in cold periods, they lower the freezing point of sap (Navarro and Navarro, 2000).This is an experiment to study the influence of soil management techniques on the monovalent cations in soil solutions at different depths. The cropping systems studied are conventional tillage, minimum tillage and direct drilling.Conventional tillage releases more Na+ and K+ to the soil solution than the conservative techniques. In the case of Na+, the conventional tillage soil solution has an average concentration of 0.563 meq/L compared to 0.303 meq/L of minimum tillage and 0.340 meq/L of direct drilling. As for the K+, the soil solution concentration of conventional tillage is 0.097 meq/L, compared to 0.079 meq/L of the solution of minimum tillage and 0.056 meq/L of direct drilling.The behavior for the two cations studied is distinct at different depths. The Na+ is more abundant in water samples of soil taken in depth. Therefore, the salinization risk may take place in the subsoil, especially in conventional tillage where the Bw1 horizon values are three times higher than in the Ap horizon, while the K+ is more abundant in the surface horizon. Conventional tillage and minimum tillage techniques, in the Ap horizon have a similar pattern with a K+ concentration average of 0.15 meq/L and 0.14 meq/L, respectively, resulting in lower values for direct drilling.Studies on clay soils have not been performed previously because of the difficulty presented by these soils when soil solution extracted for analysis. We analyzed the monovalent cations (sodium and potassium) from soil solution; because the soil solution is the immediate source of sodium and potassium for plants.

Research Highlights
► Using soil blocks we analyzed sodium and potassium from soil solution.
► CT releases more Na+ and K+ to the soil solution than the conservative techniques.
► The behavior for the two cations studied is distinct at different depths.
► We recommend MT because there is no risk of salinization and releases more K+ than DD.