Extraction of K From Illinois Soil by Electro-Ultra-Filtration

Illinois Fertilizer Conference Proceedings
January 23-25, 1995

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Extraction of K From Illinois Soil by Electro-Ultra-Filtration

Ted R. Peck and Marilyn E. Sullivan¹

Introduction

Electro-Ultra filtration (E. U. F.) is a laboratory apparatus for expediting a water extract of soil. It is a three cell apparatus as shown in figure 1. The middle cell contains the soil suspension being tested (soil:water of 1:10) with a stirrer, water in flow, and temperature regulation. Each side of the middle cell, is a cell provided with a micropore filter affixed to an electrode grid with the anode on one side and the cathode on the other. The cations accumulating at the cathode and the anions at the anode are periodically flushed to collecting tanks by a stream of water. The first six fractions are collected at conditions of room temperature and a voltage of 200. Fractions 7 and 8 are collected at 80°C and 400 volts.

The objective of this report is to show the E.U.F. extractable potassium as effected by a temperature change, voltage change, condition of the soil sample, whether dried or undried, and relationship of extractable potassium with the conventional ammonium acetate extraction during selected field soil sampling times of the year.

Materials and Methods

The study this year utilized a location on the Agronomy/Plant Pathology South Farm, Urbana 11. of a pre-existing land area devoted to K rate build-up 1970 through 1983 and residual since while cropped to an alternation of corn and soybean. During the 14 year build-up period, annual K rates were 0, 50, 150, 200, and 2501b K₂O/acre.

Results and Discussion

Typical E.U.F. extractable potassium amounts are shown in figures 2,3,4, and 5. Figures 2 and 3 differ in that the temperature of the soil suspension is at 80°C in the extraction of fractions 7 and 8 shown in figure 2 while the temperature of the soil suspension is consistently at room temperature (about 20°C) in figure 3 for all fractions. Higher temperature increases potassium extraction as compared to higher voltage which shows little change in K extraction. This is consistent over the different historical K rate treatments.

Figures 4 and 5 differ from figures 2 and 3, respectively in that undried, field moist soil were used for extraction in figures 4 and 5 as compared to air dried soil used for the extraction in figures 2 and 3. The E.U.F. extraction of potassium is consistent with other extractions in showing an increase in extractable K with drying of the soil sample. Differences are consistent over the different historical K rate treatments.

Seasonal E.U.F. extractable K and conventional ammonium acetate K soil tests on field moist and dried soil are shown in figures 6, 7, 8, 9, and 10. The figures differ in representing different K rate treatments. The E.U.F. K extraction is the summation of the first six fractions (as shown in figures 2, 3, 4, and 5). A good relationship of the two test methods are shown in figures 6, 7, 8, 9, and 10. The statistics indicate slightly higher "simple r values" for the two tests performed on field moist (undried soil) than on dried soil.

At this stage of the study, the E.U.F. method is not giving improved understanding of the bonding energy of K in soil but it is corroborating status of the conventional testing methods.