Degree Type


Date of Award


Degree Name

Master of Science



First Advisor

Antonio P. Mallarino


Better information is needed about soil-test K and K removed with harvest because these are used to determine K fertilization rates. This study evaluated relationships between K fertilization, grain yield, grain K concentration, K removal, and soil-test K were studied in five sites with typical Iowa soils from 1994 to 2009 for corn (Zea mays L.) - soybean (Glycine max L.) rotations managed with no-tillage. Treatments were a control receiving no K, and broadcast K rates (potassium chloride fertilizer) of 33 and 66 kg K ha-1. Soil-test K was measured each year in two depths of soil (0 - 7.5 and 7.5 - 15 cm) by sampling all plots receiving no K and plots receiving the highest K rate before the corn year. Soil samples also were collected from depths of 0-5, 5-10, 10-15, and 15-30 cm at the end of last year of the study. Yield responses to K fertilization were frequent and large only at three sites where soil-test K (0-15 cm) of non-fertilized plots tested less than 170 mg K kg-1. Potassium fertilization effects on grain K concentration were observed in several years for both crops, but increases were small and sometimes the concentration was decreased. Mean grain K concentration was 16.3 and 3.2 g K kg-1 for corn and soybean, respectively, which were lower than currently assumed averages in Iowa. Grain yield was not correlated with K concentration but was linearly correlated with K removal with harvest. Trends over time of K removal and soil-test K were well correlated over the long term, but not from year to year. There was large stratification in fertilized plots at all sites, but the stratification increased over the 16 years of the study only at one site where the highest K rate increased soil-test K significantly over time. The results indicated that good yield estimates are more important than grain K concentration to estimate grain K removal across fields and years, and also that there is good correlation between K removal and soil-test K only over the long-term.


Copyright Owner

Carlos Xavier Villavicencio



Date Available


File Format


File Size

54 pages