Illinois Fertilizer
Conference Proceedings
January 25-27, 1993
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Ted R. Peck and Marilyn E. Sullivan1
Electo-Ultra-Filtration (EUF) is a three cell apparatus (1). The middle cell contains the soil suspension being tested (soil:water of 1:10) with a stirrer, water inflow, and temperature regulation. Each side of the middle cell is a cell provided with a micropore filter attached to electrodes 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 continuously flushed to collecting tanks by a stream of water. Increasing the voltage at 5 to 30 minute intervals can result in characterizing nutrient amounts held at different bonding energies.
Questions about Illinois soil K levels are increasing. Additions of fertilizer
K as "build-up" generally results in increased soil levels but wide
spread usage of soil testing brings to light fields where the soil K levels
do not change with fertilization. In Illinois, crop response to K fertilization
has been an increasing factor since 1950. Annual K fertilizer added to Illinois
soils has exceeded estimated annual removal of K in the grain of corn, soybeans
and wheat since the mid-1960's. Better understanding of K reactions in Illinois
soils is needed and E.U.F. has potential to be helpful.
The study utilizes pre-existing land areas devoted to K rate build-up since 1966 at the Brownstown Research Center, since 1967 at Northern Illinois Research Center, and since 1970 at the Agronomy/Plant Pathology South Farm, Urbana, IL. Soil type is Cisne silt loam at Brownstown and Drummer silty clay loam at the other two locations. E.U.F. desorbed K fractions will be determined along with soil K extracted with NH4OAc, boiling HNO3, exhaustive leaching and exhaustive cropping.
E.U.F. apparatus is being set up and pots are being set up in the greenhouse for exhaustive cropping. Preliminary chemical analyses of the K study at the Brownstown Field Research Center are shown in table 1.
Item [1] identifies the plots as a part of the major series of soil fertility studies on the Research Center with known history back to 1937.
Item [2] identifies the annual K fertilizer rate applied to the plots beginning in 1966 and it was last applied in the fall of 1987. The K2O basis of the respective rates are 40, 80, 120 and 160.
Item [3] sums the addition of K during the period 1966 to 1983 (since the following analyses were performed on soil samples after the 1983 crop season).
Item [4] reflects the crop removal of K from the plots in the harvested portion of crops. The crop rotation is corn, soybeans, and winter wheat with double crop soybeans starting in 1974. Crop removal is estimated on the basis of 0.23 pound per bushel of corn, 1.07 lb per bushel of soybean and 0.25 pound per bushel of wheat. Crop response to applied K was limited to the lowest K rate in the study. More K than is shown in table 1 would be required to grow the crop plant but the K in the roots and vegetative part of plants is recycled in succeeding years plants.
Item [5] is the standard plant available soil test. During this study period, soil K tests from soil samples taken in all years except 1974 and 1981 are known. Test levels increased markedly during the first two years, 1967 and 1968, and stayed relatively stable the remainder of the study over all rates of K applied.
Item [6] is the total K in the soil determined using a bomb digestion procedure. K rates applied in this study do not affect the total K level.
Item [7] is believed to be non-readily-plant-available, non-exchangeable inter-lattice form of soil potassium extracted with boiling nitric acid by the method of Wood and DeTurk (1). It is apparent the first digestion extracts the greater part of this form. Some literature shows a relationship of this form to the amount of K extracted by exhaustive cropping of a soil in greenhouse study.
Item [8] is also reported to approximate the amount of K extracted by exhaustive cropping. The method of Schulte (2) was used which is a slow percolation of a dilute Ca & Mg solution (approximating a composition of the soil solution). On these soils this amount of K approximates the K extracted in the standard soil K test. After leaching K, the boiling HNO3 extracted summed with the leached K is a similar amount to the 1st extraction with boiling HNO3(Item [7]).
Item [9] is a method reported by Attoe and Truog (3). They also report agreement of exhaustive cropping and the amount extracted by this method.
Item [10] is a method developed by Hunter and Pratt (4). The heat-of-dilution develops a temperature of 125°C. This method is also reported to agree with the amount of K extracted by exhaustive cropping.
Item [11] is a method developed by McLean (5) to evaluate the soil test "build-up" requirement (amount of fertilizer to change the soil test a given amount). It would be expected this should be a constant for a soil type as shown on six of the plots. The lower recovery at the highest K rate should not be expected and needs further study.
Items [12,13,14,15,16,17,& 18] are selected extractants to evaluate their extracting capacity to published extractants. It is interesting the alkaline extractants, extract lessor amounts of K than acidic extractants.
Results of these preliminary studies show general agreement in the amount of
K extracted by different extractants. This suggests there are specific and unique
forms of K in the soil, at least on this soil type.
1Professor and Research Specialist, Dept. of Agronomy, Univ. of IL, Urbana, IL.
Wood, L. K. and E. E. DeTurk. 1941, The absorption of potassium in soils in nonreplaceable forties: Soil Sci. Soc. Amer. Proc. 5:152-161.
Schulte, F. E., 1964, University of Wisconsin Ph. D. Thesis, Chemical Fractionation on Soil Potassium According to Plant Availability.
Attoe, O. J. and E. Truog, 1945, Exchangeable and acid-soluble potassium as regards availability and reciprocal relationships. Soil Sci. Soc. Amer. Proc. 10:81-86
Hunter, A. H. and P. F. Pratt, 1957, Extraction of potassium from soils by
sulfuric acid. Soil Sci. Soc. Amer. Proc. 21:595-598.
McLean, E. O., T. O. Oloya and S. L. Adams, 1979, Soil test to inventory the
initially available levels and to assess the fates of added P and K as bases
for improved fertilizer recommendations. Commun. in Soil Sci. and Plant Analysis,
10(3):623-630.
