146-3 Available Phosphorus by Five Different Soil Testing Methods and Fractionation In Southwest Florida Vegetable Production.



Monday, October 17, 2011: 8:35 AM
Henry Gonzalez Convention Center, Room 213A, Concourse Level

Shinjiro Sato1, Kelly Morgan2, Kamal Mahmoud2, Smita Barkataky2 and Assma Zekri2, (1)Soka University, Hachioji-shi, Tokyo, Japan
(2)Southwest Florida Research and Education Center, University of Florida, Immokalee, FL
Under Best Management Practice (BMP) program developed by the University of Florida, recommendations for phosphorus (P) fertilizer management are based on Mehlich-1 (M1) soil test P levels of the production site at the beginning of the season. However, most vegetables in southwest Florida are grown on soils belonging to Alfisols or Spodosols with argillic (clay) or spodic (organic hardpan) sub-surface. The M1-P may not represent adequate available P thus provide accurate justifications for the recommendation in alkaline and calcareous soils. Therefore, soils (0-6” and 6-12”) were collected from vegetable production sites in southwest Florida for 3 years and available P by five different soil testing methods: M1, Mehlich-3 (M3), Bray-1, Olsen, and ammonium bicarbonate-DTPA (AB-DTPA) were analyzed. Sequential fractionation analyses of the same soil samples (n=1208) were also performed. Correlation coefficients (r2) between available P by the five testing methods and the labile P (the sum of water- and bicarbonate-extractable P) ranged between 0.396 and 0.675 with the M3 P being the best for non-calcareous soils (from Farm 1), but worsened to be between 0.032 and 0.294 for calcareous soils (from Farm 2) with the M3 being the best. However, the water-extractable P only correlated best with AB-DTPA P for the non-calcareous soils (r2=0.668), and Olsen P for the calcareous soils (r2=0.555). Depending on which soil testing method best represents plant available P, current BMP P recommendations for southwest Florida vegetable production should be revised.
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