Sugarcane Yield Response to Potassium on Florida Histosols.

Potassium is a primary plant nutrient and is used in relatively large amounts in Florida sugarcane (Saccharum spp.) so that it is a large portion of a grower’s fertilizer budget. Current potassium fertilizer recommendations for Florida sugarcane on organic soils are based on research conducted more than 40 years ago when these soils had lower pH and were deeper to limestone bedrock. Recommendations range up to 232 kg K ha-1 and are based on pre-plant soil test values. The objective of this study was to determine sugarcane yield response to potassium fertilizer application on Florida organic soils (Histosols). The study was comprised of six experiments throughout the Everglades Agricultural Area, with all trials using randomized complete block designs with six replications. Potassium fertilizer treatments were single annual banded applications of muriate of potash (KCl) at rates of 0, 46, 93, 139, 186, 232, and 279 kg K ha-1 for sites 1-5. Site 6 included all these rates except the 46 kg K ha-1 rate. Potassium rate significantly influenced tons cane ha-1 (TCH), tons sucrose ha-1 (TSH), and kg sucrose ton-1 cane, with the site X K rate interaction being significant for TCH and TSH. A linear plateau model indicated that there was a positive sucrose yield response to K fertilizer up to 97 g K m-3 for pre-crop 0.5 N acetic acid-extractable soil K. This value is 12% less than the minimum soil test value currently corresponding to a zero K fertilizer recommendation for plant cane. The maximum estimated K fertilizer requirement in the study was 170 kg K ha-1 for first ratoon at a site with initial soil test K of 20 g K m-3. Results confirm the importance of potassium in sugarcane fertilization programs and the relationships developed will be used to adjust fertilizer recommendations for growers.