SIMULTANEOUS EXTRACTION OF AVAILABLE PHOSPHORUS AND POTASSIUM WITH A NEW SOIL TEST - A MODIFICATION OF KELOWNA EXTRACTION

The objective of this study was to evaluate a new soil test for simultaneous extraction of available phosphorus (P) and potassium (K) in soils. The new soil test is a modification of the Kelowna extraction. The modified Kelowna (KM) extractant is composed of 0.025M HOAc and 0.25M NH4OAc as well as 0.015M NH4F with a measured pH of 4.9. The KM test was compared to the Olsen 0.5M sodium bicarbonate extraction. In order to provide maximum contrast in nutrient availability and soil properties, four hundred soil samples from all six soil zones in Saskatchewan were selected to be tested. Thirty eight of the samples were also used for growth chamber study to compare plant response to the new test. Results showed P and K extracted by the new method to be highly and significantly correlated with the Olsen-extractable P and K (r2 = 0.92*** and 0.85***). Results also showed higher correlations between test-predicted P and K availability and actual plant uptake for the new method (r2 = 0.76*** and 0.56***) compared to the Olsen test (r2 = 0.67*** and 0.38***).