20 Nov 2009

Effects of Potassium Fertilization of Soybean Grain Yield and Disease Incidence in Iowa


This project was conducted from 2005 until 2008 at five Iowa locations (20 site-years) to assess the effects of K fertilization and tillage on soybean grain yield and incidence of leaf/stem diseases. Rates of 0, 35, 70, and 140 lb K2O/A were broadcast at four locations, and the lowest three K rates were broadcast or deep-banded at the other location. Soybean was grown in rotation with corn, and treatments were evaluated each year. Soybean varieties varied across trials and were planted using a 30-in. row spacing.

There was a large grain yield response to K in low-testing soils (< 131 ppm K, 6-in. depth), a small response in soils testing optimum (131 to 170 ppm K, for which only maintenance is recommended), and no response in high-testing soils. Tillage did not affect grain yield or yield response to K fertilization. Potassium deficiency symptoms were obvious on low-testing plots of several site-years. Asian Soybean Rust was not detected at any site. There was light to moderate incidence of Brown Leaf Spot and Bacterial Blight in most locations and years, and less frequent incidence of Cercospora Leaf Spot, Frogeye Leaf Spot, and Powdery Mildew. Tillage sometimes influenced disease incidence, but effects were inconsistent across diseases, locations, and years and are not discussed in this summary.

Effects of Potassium Fertilization of Soybean Grain Yield and Disease Incidence in Iowa IA 13F.pdf