146-4 Extractable Soil Phosphorus Related to Phosphorus Fractions and Sugarcane Yield On Florida Histosols.



Monday, October 17, 2011: 8:50 AM
Henry Gonzalez Convention Center, Room 213A, Concourse Level

Mabry McCray1, Alan Wright2, Ronald Rice3, Yigang Luo4 and Shangning Ji4, (1)Agronomy, University of Florida, Belle Glade, FL
(2)Soil and Water Science, University of Florida, Belle Glade, FL
(3)UF/IFAS Palm Beach County Extension Service, University of Florida, Belle Glade, FL
(4)University of Florida, Belle Glade, FL
Optimizing P fertilizer recommendations with proper soil testing will reduce over-application and in south Florida is vital for reducing P discharge into the Everglades. Five field experiments were conducted on different organic soils in the Everglades Agricultural Area with the objectives of 1) quantifying the forms of soil P and 2) relating extractable P using water, acetic acid, Bray 2, and Mehlich 3 extractants to these P fractions. Results of two additional P rate experiments were added to the dataset to further evaluate the relationships between extractable P and relative sucrose yield of sugarcane (Saccharum spp.). The percentages of five P fractions generally increased with increasing recalcitrance in the order of labile P, Fe-Al bound P, humic-fulvic bound P, Ca-Mg bound P, and residual P with the exceptions of two acid soils in which the highest percentage of total P was in the humic-fulvic fraction. The water extractant measured only labile P with a large increase in extractable P at pH<6. Acetic acid-extractable P included some of the more recalcitrant forms of soil P, residual P and possibly Ca-Mg bound P, and was assumed to extract the most P not considered plant available. Bray 2 primarily extracted labile P and Fe-Al bound P with possible contribution from humic-fulvic bound P and residual P. Mehlich 3 was the only extractant tested which included labile and non-labile (primarily Fe-Al bound) P while excluding residual P, thus was deemed to best indicate the plant-available P pool. Mehlich 3 also related best to relative sucrose yield and a new soil test calibration is proposed with a maximum rate of 36 kg P ha-1 with < 10 g P m-3 in pre-plant soil samples and no P recommended with > 30 g P m-3.
See more from this Division: S08 Nutrient Management & Soil & Plant Analysis
See more from this Session: Soil and Plant Analysis: Tools for Improved Nutrient Management I