Stabilizing Soil Aggregates with Phosphoric Acid
1976
Thien, Steve J.
Four P-containing fertilizer materials (H₃PO₄, liquid and dry ammonium polyphosphate, and triple superphosphate) were compared for ability to increase water stability of aggregates in an acid soil. Only agricultural-grade H₃PO₄ significantly increased aggregate stability—from 6.2% in the untreated samples to 45.2% in samples treated with 228 kg P/ha. The induced stability lasted through at least five wetting and drying cycles, each cycle consisting of 1.8 cm of water applied over a 1-hour period followed by 2 weeks of air drying. Water stability of soil aggregates treated with H₃PO₄ increased as H₃PO₄ was increased to 228 kg P/ha (maximum tested). Exchangeable Al increased from 0.2 ppm Al in untreated soil to 2.55 and 2.85 ppm Al in soil layers receiving 112 and 224 kg P/ha, respectively. While the highest P concentrations tested caused soil pH to temporarily drop approximately one unit, pH returned to the pretreated value after four wetting cycles. Scanning electron microscope photos showed more fine particles present in the treated aggregates than in the untreated samples. Phosphoric acid apparently modifies the soil physical environment by preserving the fine-particle content of aggregates which in turn increases their water stability.
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