Potassium Movement and Uptake as Affected by Potassium Source and Placement

Abstract

Although downward loss of anions such as nitrate has been well-studied in high-sand turfgrass putting greens, leaching of cations such as potassium (K) has received less study. Moreover, turfgrass research with K has largely focused on two soluble forms of K: potassium chloride (KCl) and potassium sulfate (K2SO4). Thus, the objectives of this research project were to: 1) examine the effect of K fertilizer sources on bentgrass (Agrostis palustris Huds.) performance, 2) determine K levels in soil and plant tissue, and, 3) trace downward movement of K via incremental depth sampling. The 2 yr study was conducted on a 5 yr old existing bentgrass putting green (cv 'G2'), with treatments arranged in a randomized complete block design with 4 replications of each treatment. Treatments were K sources: 1) potassium chloride - KCl, 2) potassium sulfate - K2SO4, 3) resin-coated K2SO4, 4) potassium thiosulfate (KTS), and, 5) potassium nitrate - KNO3. All K treatments were applied quarterly, with treatments applied according to the initial recommended soil-test level of 56 kg ha-1 K2O. Treatments were applied either by a broadcast application or a vertical 'band' treatment. For the band treatment plots were first core aerified (1 cm diam. x 10 cm deep), and applied fertilizer was swept into aerification holes, followed by a sand topdressing. Broadcast treatments were also aerified, with topdress sand first applied, and K fertilizer then surface applied. Collected data included monthly clipping yield, monthly K content in clippings, monthly soil K (0-7 cm sampling depth), quarterly shoot density, and quarterly root mass. Extractable soil K over a 0-30 cm depth was also collected quarterly, with samples collected every 5 cm of depth. Over the 2 year study potassium application had no beneficial effects on turfgrass performance, and acceptable performance was achieved across a wide gradient of K content in soil and leaf tissue. Regardless of soil test K level, no deficiency symptoms were observed.