FACTORS AFFECTING POTASSIUM STATUS OF ALLUVIAL-DERIVED SOILS OF WESTERN IOWA

Alluvial-derived soils of the Missouri River floodplain of western Iow a have greater amounts of available K (AVK), determined by a slurry me thod, and exchangeable K (EXK) than major upland soils, This research was conducted to better understand the high K status of these soils. F ive soil series from Monona County in western Iowa were investigated. The soils differ in relative age and textural class. Soils formed on t he lower geomorphic surface have more AVK than the soils formed on the higher geomorphic surface. The variation in pedogenic development of soils on geomorphic surfaces was sufficient to cause differences in th e K status of these soils. Correlation coefficient analysis of the dat a indicates that AVK is related to EXK. Correlation coefficients of AV K and EXK were improved when soils were divided into three textural cl asses. The improvement of correlation coefficients suggests that parti cle-size fractions and EXK are controlling factors for the higher AVK content. Sand, silt, and clay contents and EXK were used in developing multiple linear regression equations to predict AVK for these soils. This study suggests that clay contents and EXK should be considered fo r future K-fertilizer recommendations for alluvial-derived soils of th e Missouri River floodplain.