Accompanying cations and anions affect the diffusive transport of phosphate in a model calcareous soil system
Bibliographic record
Abstract
Mixing non-phosphate salts with phosphate fertilizer modifies the chemical environment of the soil-phosphorus (P) fertilizer reaction zone due to induced changes in soil pH and the interactions of P with soil components and other ions. The objective of this study was to examine the effects of cation and anion interactions on the solubility and diffusive transport of P in columns packed with a mixture of inert quartz sand and Ca2+-saturated cation exchange resin, buffered with CaCO3. The background pH of the resin-sand mixture was 9.4. Three types of cations (K+, NH4+, and Mg2+) were combined with four anions (NO3-, Cl-, SO42-, and CO32-) to produce 12 non-phosphate salts. Each of these salts was mixed with 0.4 g of KH2PO4 to provide 408.9 mg P kg-1 soil. The experiment was carried out in three replicates. Following 2 wk of incubation, columns were sectioned at 3-mm intervals and the pH of each section was measured. The samples were extracted with deionized water and subsequently with 1 mol L-1 HCl. Addition of KH2PO4 alone reduced the pH at the surface (first 3-mm section) of the resin-sand column to 7.1, while pH remained unchanged at 9.1 on addition of K2CO3 and KH2PO4. Addition of MgCl2 and KH2PO4 resulted in the lowest pH in the column and the greatest depth of H+ penetration compared with other treatments. None of the treatments containing NO3- or Cl- salts enhanced the solubility and movement of P. Addition of (NH4)2SO4 or (NH4)2CO3 to KH2PO4 produced the greatest amount of water-extractable P, followed by K2SO4. The lowest solubility of P occurred on addition of K2CO3 (P < 0.05). We attributed the enhanced solubility of P by SO42- and CO32- associated with NH4+ to competition between these anions and HPO42- for precipitation with solution Ca2+. Phosphate ion moved to depths of 5.0, 6.0 and 7.5 cm on addition of K2SO4, (NH4)2SO4, and MgSO4 to the column, respectively. These results suggested that salts such as K2SO4, (NH4)2CO3, (NH4)2SO4 and MgSO4 would enhance the lability of fertilizer P in a calcareous soil system. Key words: Solubility, precipitation, diffusive transport, resin, cation exchange, anion competition, dual banding
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".