Clover Residue Effectiveness in Reducing Orthophosphate Sorption on Ferric Hydroxide Coated Soil
In many tropical soil systems, secondary minerals are coated with sesquioxides, resulting in inherently low P availability to plants due to P-fixation mechanisms. Research was conducted to determine the influence of hydroponically grown clover (Trifolium repens L.) residue pretreatment in reducing orthophosphate sorption on a fine-loamy, siliceous, thermic Typic Paleudult (Orangeburg series) that had been coated with synthetically prepared amorphous Fe(OH)3. A 3 × 2 × 3 factorial experiment was conducted in split-split-plot design with P as the main plot, Fe(OH)3 as the subplot, and clover as the sub-subplot. Throughout two cropping periods of 50 d each, to assess the initial and residual effect of clover pretreatment, corn (Zea mays L.) dry-matter yield, P uptake, and Bray 2 extractable P levels were superior with clover pretreatment prior to P fertilizer addition. When fertilizers, but not clover, were again applied to experimental units for a third cropping period, clover pretreatment did not influence plant dry-matter accumulation or P uptake. It did, however, substantially increase Bray 2 extractable P levels. Potentiometric titrations relating to surface charge were conducted on treatments with Fe(OH)3 that had been amended with P, clover, and P plus clover after the first cropping period. Results suggest that organic acids from clover decomposition bind to Fe(OH)3 surfaces and are able to complex Lewis acid cations to increase P availability.
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