Cotton response to in-row subsoiling and potassium fertilizer placement in Alabama

In the USA a suggested method for correcting late season K deficiencies in cotton (Gossypium hirsutum L.) is by in-row deep placement of K fertilizer. Experiments were conducted on three Alabama soils (southeastern USA) for 3 years to evaluate cotton response to K fertilizer when surface broadcast with and without in-row subsoiling (to 38 cm depth) or deep placed in the in-row subsoil channel. Potassium was applied at rates ranging from 0 to 84 kg K ha⁻¹. Deep placement was achieved with a fertilizer applicator developed to distribute dry fertilizer at three depths down the back of the subsoil shank. All three soils also had deep placement treatments of 1680 kg ha⁻¹ agricultural limestone with and without 84 kg K ha⁻¹. Soils were an Emory silt loam (fine-silty, siliceous Fluventic Umbric Dystrochrepts), a Norfolk sandy loam (fine-loamy, siliceous Typic Kandiudults), and a Lucedale sandy clay loam (fine-loamy, siliceous Rhodic Paleuduts). All three soils had medium soil test K concentrations in the plow layer and medium or low concentrations of K at greater depths. The Norfolk soil had a well-developed traffic pan and in-row subsoiling increased seed cotton yields by an average of 22% during the 3 years of the study. Cotton responded to K fertilization in 2 out of 3 years at each location (6 out of 9 site-years) regardless of the method of K application. Annual applications of 84 kg K ha⁻¹ increased 3 year average seed cotton yields by 17%, 10% and 19% on the Emory, Norfolk and Lucedale soils, respectively. Deep placement of agricultural limestone with or without K fertilizer for cotton did not increase cotton yields.