Phosphorus leaching in a calcareous soil treated with plant residues and inorganic fertilizer
2011
Jalali, Mohsen | Karamnejad, Ladan
Column experiments were conducted over 45 d to determine the degree of P mobility. The sandy loam soil was spiked with 200 mg P kg⁻¹ and 5% organic residues. The treatments included: control without any water-soluble P and plant residues, potato, wheat, water-soluble P fertilizer, wheat + water-soluble P, and potato + water-soluble P. Each column was leached with distilled water, and leachates were collected and analyzed for P, K⁺, Ca²⁺, Mg²⁺, along with pH and EC. Sequential extraction was performed on soil samples at the end of leaching column experiments. The relatively high initial concentration of P in the leachates decreased to more stable values after 15 d which can be attributed to the colloid-bound P. The P concentrations in the leachates fluctuated between 8 and 220 mg L⁻¹ in the water-soluble-P fertilizer treatment, between 0.80 and 230 mg L⁻¹ in the potato + water-soluble-P treatment, and between 0.90 and 214 mg L⁻¹ in the wheat + water-soluble P treatment. Leaching loss of P mainly occurred in the 15 d of leaching, accounting for 94%, 88%, and 65% of total P leached in wheat + water-soluble-P, potato + water-soluble-P, and water-soluble-P treatments, respectively. Maximum amount of P leached was found from an exponential kind model and was in the range 0.45 mg kg⁻¹ to 125.4 mg kg⁻¹ in control and potato + water-soluble-P treatments, respectively. Sequential extraction results showed that in control and amended soils the major proportion of P was associated with Ca. The leachate samples in all treatments were saturated with respect to hydroxyapatite, β-tricalcium phosphate, and octacalcium phosphate up to 20 d of leaching, whereas they were undersaturated with respect to Mg-P minerals through the entire leaching experiment.
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