POTASSIUM STATUS OF SOME QUEBEC SOILS: K RELEASED BY NITRIC ACID AND SODIUM TETRAPHENYLBORON AS RELATED TO PARTICLE SIZE AND MINERALOGY

Abstract

The K release characteristics of surface samples from five Quebec soils were investigated. Each soil was fractionated by size into six separates. Each separate was extracted with 1 M ammonium acetate (NH 4 OAc), with 1 M nitric acid (HNO 3 ) and with sodium tetraphenylboron (NaTPB) and the K extracted was determined. The clay separates contained most of the HNO 3 and NaTPB-extractable K. The average amounts of K removed by 1 M HNO 3 and NaTPB from the clay was up to 16 times more than that released from silt or sand fractions. The strong relationship between extractable K and clay content was probably due to the similarity in mineralogical composition and degree of weathering of these soils. Clay-sized chlorite and vermiculite were destroyed by the HNO 3 extraction but not by the NaTPB extraction. Crop response to K fertilizer was generally reduced as clay content and extractable K increased. Key words: Extractable K, NaTPB-K, HNO 3 -K