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Title: PHYSICAL AND CHEMICAL PROPERTIES OF FRAGIPAN HORIZON MATERIALS AMENDED WITH FLUIDIZED BED COMBUSTION ASH

Author
item Rhoton, Fred
item Edwards Jr, James - Jim
item Norton, Lloyd

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: The sustainability of fragipan soils is dependent upon the development of a method to remove the silica which cements fragipans so strongly that plant roots and water cannot penetrate to the lower profile depths. Fragipan samples were mixed with a high pH fluidized bed combustion ash material to solubilize the silica. After equilibrating for up to one year, the ash material appeared to reduce fragipan strength by the formation of microaggregates. Use of these byproduct ash materials has the potential to degrade fragipans and increase plant rooting depths and water storage capacity.

Technical Abstract: Fragipan horizon strength, which has been attributed to Si cementation, limits soil productivity by restricting the depth of root growth and water movement. Thus, fluidized bed combustion (FBC) ash was evaluated as a potential amendment to dissolve the cementing agent and decrease the strength of the horizon. Fragipan samples (<2 mm) weighing 1.5 kg were mixed with FBC ash (<0.5 mm) at rates of 0, 11.2, 22.4, and 44.8 Mg ha-1, placed in 1650 cm3 cylinders, and wetted to 40% of the sample weight with distilled water. Five replicates were prepared for each treatment. The cylinders were sealed and equilibrated for periods 30, 90, 180, and 365 d. At each time interval, soil materials were characterized for strength by modulus of rupture (MR), slaking rate, pH, and extractable Fe, Al, Si, Ca and Mg. Soil solutions were analyzed for the dissolved component of the same elements. After 365 d, MR for the 0, 11.2, 22.4, and 44.8 Mg ha-1 amendment rates averaged 0.43, 1.02, 0.85, and 0.47 MPa, respectively. Slaking rates for the same samples were 0.30, 0.19, 0.22, and 0.20 g sec-1. Dissolved Si and Mg in the extracts exhibited the most consistent response to treatment. Silica concentrations were 31.0, 7.6, 5.1, and 3.6 mg kg-1, while Mg contents equaled 0.19, 164.0, 77.4, and 12.8 mg kg-1, respectively. The data indicate that FBC ash did not appear to have a direct effect on soil strength relative to dissolving amorphous Si cementing agents. Instead, there are indications that FBC ash may have contributed to the formation of microaggregates that improved structure to the extent that soil strength was reduced at the 44.8 Mg ha-1 rate.