PHOSPHORUS UPTAKE BY BAHIAGRASS FROM SPODOSOLS - MODELING OF UPTAKE FROM DIFFERENT HORIZONS

Bahiagrass (Paspalum notatum Flugge), when grown on a Myakka fine sand in Florida (sandy, siliceous, hyperthermic Aeric Alaquod), did not re spond to P fertilization even though Mehlich-1 extractable P was low i n the surface soil horizon. Previous research suggested that the Bh ho rizon was a potential source of P. The objective of this study was to evaluate the plant availability of P in the Bh horizon and to determin e to what degree existing nutrient uptake theories explain the uptake of P by bahiagrass under greenhouse conditions. Sod and soil samples w ere collected from unfertilized bahiagrass growing on a Spodosol. Sod was replanted into soil samples. Plant and root samples were collected from unfertilized bahiagrass growing on a Spodosol. Sod was replanted into soil samples. Plant and root samples were collected at 18, 36, 6 1, and 90 d. Selected soil and plant model parameters were estimated a t each harvest period. Bahiagrass was able to extract more P from the Bh horizon material than from Ap or E horizon materials. The COMP8 com puter model was used to simulate uptake of P by bahiagrass. Observed a nd predicted P uptake by bahiagrass followed the same relative pattern (Bh > Ap > E). There was statistically good agreement between observe d and predicted P uptake for 18-d-old plants, but less agreement at 90 d (within 20%) from the Bh horizon. Predicted P uptake values from th e Ap and E were statistically lower than observed values at both harve st dates. Selected extraction procedures indicated that there was no P release from the mineral forms in the Ap horizon. Data suggest the pl ant-induced mineralization was an important P supplying mechanism in t his pot study.