Use of Green Solvents in Shaking and Ultrasound Assisted Extraction of Mobile and Mobilizable Fractions of Potassium From Soil

Abstract

Extraction of potassium from agricultural soil often involves strong acids (HCl, HNO 3 , H 2 SO 4 , HClO 4 , HF), whose decomposition results in formation of toxic gases. Green solvents are environmentally friendly and are used in place of conventional solvents that are hazardous to both human and the environment. Also, potassium in agricultural soils is often incorporated in minerals that are highly insoluble, and thus highly unavailable to plants. Usage of strong acids may result in much higher concentrations of potassium, and a wrong insight into potassium bioavailability. This erroneous result for the potassium content could lead to improper usage of fertilizers. The most important fractions of potassium for plant growth are mobile an easily mobilizable fractions. Those fractions are extracted with water and weak acids. Technique for sample preparation that is often used is shaking and ultrasound assisted extraction. In this research, two green extraction solutions with two different extraction mechanisms and two different soil types were used. All results were compared to pseudo-total amounts of metals. pH, EC, moisture content and Al -solution extracted potassium (available to plants), as basic quality parameters were measured. Potassium content was measured by means of flame atomic emission spectroscopy (FAES). Mobile and easily mobilizable fractions correlate to a high extent (r <0.800), but they are negatively correlated to pseudo-total amounts. Pseudo-total amount gives a wrong insight into the content of potassium available to plants. The ultrasound filed could be used in case of soils that are low in a clay content.