Effects of Lime, Silicate, and Phosphorus Applications to an Oxisol on Phosphorus Sorption and Ion Retention1
- T. Jot Smyth and
- Pedro A. Sanchez2
Greenhouse and laboratory experiments conducted with a clayey kaolinitic isohyperthermic Typic Haplustox from the Cerrado region of Brazil showed that CaCO3, CaSiO3, and previous P applications decreased P fixation and improved cation retention properties. The amendments were added at rates to replace 1 or 2× exchangeable Al, and P was applied at rates to provide equilibrium solution concentrations of 0, 0.05, 0.1, and 0.2 ppm P. Six months after application, CaCO3 and CaSiO3 at 1× exchangeable Al decreased the amount of previous P sorbed to provide 0.1 ppm P in solution by 18 and 24%, respectively. Previous P applications were more effective in decreasing P sorption than the amendments. A 540 ppm P rate decreased P sorption by 65% without amendments. The combination of amendments + 540 ppm P decreased P sorption by 85 to 91%. Fertilizer P recommendations based on soil solution levels for limed soils should be obtained with soil samples which have also been limed; otherwise the P requirement may be overestimated.
Net negative soil charges increased by 11 to 47% with amendment applications and by 34% with 540 ppm P. The highest P and amendment rates doubled the net negative charge of this soil. Joint applications of P and soil amendments increased the negative charge and decreased the positive charge to a greater extent than when applied separately. Applications of both P and amendments made a major improvement in cation retention against leaching, but may increase anion leaching. P applications significantly increased soil pH and negative ΔpH values.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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