This incubation study mixed farmland soil from near a rare earth tailings site in southwest China with compost made from kiwifruit branches and sheep manure, then tracked lanthanum and cerium across five sequential extraction fractions for 28 days. Compost shifted both elements from exchangeable, carbonate-bound and iron-manganese-oxide-bound fractions toward residual forms, with larger effects at higher compost ratios.
Key numbers
- Test soil total lanthanum about 29.0 mg/kg and total cerium about 67.6 mg/kg (Methods and Table 2, p. 7).
- Mobile (exchangeable plus carbonate-bound plus iron-manganese-oxide-bound) lanthanum on day 28: 3.868 mg/kg (13.8% of total) at 0% compost, 2.507 mg/kg (9.9%) at 10%, and 0.597 mg/kg (4.3%) at 50% compost (p. 5).
- Mobile cerium on day 28: 5.476 mg/kg (8.1%) at 0% compost, 3.85 mg/kg (6.3%) at 10%, and 0.985 mg/kg (2.9%) at 50% compost (p. 5). The text labels the cerium percentages as lanthanum, apparently a typographical slip.
- The authors suggest a 10% compost ratio as a practical choice for cultivation and cost (abstract).
Methods (brief)
Air-dried topsoil (0 to 20 cm) from farmland near the Maoniuping rare earth tailings was mixed with 0% to 50% compost and incubated; samples were extracted by the Tessier sequential method and analyzed by ICP-MS (PerkinElmer NexION 2000) in three parallel samples.
Evidence fitness
Supports a statement that organic amendment can reduce the extractable, more mobile share of lanthanum and cerium in soil over weeks. It does not show reduced uptake by crops or lower levels in food, and part of the concentration decline is dilution by compost, which the authors acknowledge.
Limitations
Laboratory incubation of one soil for 28 days; no plants grown; extraction fractions are operational, not direct measures of plant availability; no quality control samples reported.
Related evidence
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