Sugarcane yield response to potassium fertilization as related to extractable soil potassium on Florida mineral soils

Potassium (K) is required in large amounts for sugarcane (Saccharum spp.), but K is rapidly leached in Florida mineral soils, which account for 29% of sugarcane production in the state. This study was conducted to (a) determine sucrose yield response to K fertilizer rates from 0 to 279 kg K ha(-1), and (b) relate sucrose yield to soil-extractable K on Florida mineral soils using 0.5 M acetic acid, 0.7 M ammonium acetate, and Mehlich 3. Field small-plot (83 or 121 m(2)) trials were conducted at six locations including three Spodosols, two Alfisols, and one Entisol. All experiments were randomized complete block designs with seven K fertilizer rates and six replications. Potassium was applied as granular muriate of potash with four split applications for plant cane and three splits for ratoon crops. Significant sucrose yield responses were determined at five of six locations and all sites had insufficient K without K fertilizer application. Relative sucrose yield reached a plateau at leaf concentration of 8.2 g K kg(-1). Linear and quadratic models were used to determine that K fertilizer requirement ranged from 139 to 232 kg K ha(-1). Relationships among soil K with the three extractants were strong and indicated that any of these could be used to determine available soil K. Relationships of extractable soil K with relative sucrose yield and leaf K concentration were developed that can be used to develop a calibrated soil test for Florida mineral soils.