IN-ROW SUBSOILING AND POTASSIUM PLACEMENT EFFECTS ON ROOT-GROWTH AND POTASSIUM CONTENT OF COTTON

One method of correcting K deficiencies in cotton (Gossypium hirsutum L.) is by in-row deep placement of K fertilizer. At present, the mechanisms involved in cotton yield response to deep placement of K have not been elucidated. A field study was conducted in 1990 and 1991 to evaluate root development and dry matter yield of cotton as affected by in-row subsoiling and placement of K fertilizer. The experiment was located in central Alabama on a Norfolk fine sandy loam (fine-loamy, siliceous, thermic Typic Kandiudult). Five treatments were compared: (i) check, without in-row subsoiling; (ii) check, with in-row subsoiling; (iii) 84 kg K ha-1 surface-applied, without in-row subsoiling; (iv) 84 kg K ha-1 surface-applied, with in-row subsoiling; and (v) 84 kg K ha-1 deep-placed, in-row. Penetrometer readings taken in 1991 demonstrated that the soil has a well-developed traffic pan at a depth of approximately 15 to 38 cm. In-row subsoiling disrupted the pan up to 25 cm away from the in-row position. Root density measurements taken in-row showed that root growth at depths > 20 cm was improved by in-row subsoiling and K fertilization. Cotton root growth at depths > 20 cm was generally better for the treatment receiving the deep applied K. However, broadcast K in combination with in-row subsoiling resulted in the highest productivity and K accumulation per plant. Results of this study suggest that, for cotton production in Alabama, deep placement of K is not superior to broadcast applications of K.