Solubility and transport of phosphate and the accompanying ions as influenced by sulphate salts in a model calcareous soil system
Bibliographic record
Abstract
Plant availability of phosphorus (P) in calcareous soil can be improved by modifying the chemical environment of the soil-P fertilizer reaction zone through the banding of non-phosphate fertilizer with P. We investigated the solubility and diffusive transport of P as influenced by addition of two sulphate salts [(NH 4 ) 2 SO 4 and K 2 SO 4 ] to NH 4 H 2 PO 4 and KH 2 PO 4 . The salts were applied to a series of wax columns packed with approximately 223 g of Ca 2+ -saturated cation exchange resin-sand mixture buffered with CaCO 3 . The background pH of the mixture was 8.8. Each treatment contained approximately 204.5 mg P kg -1 soil, while 632.3 mg SO 4 2- kg -1 soil was added to each P source for treatments containing the dual bands to provide a molar concentration of P and SO 4 2- of 6.6 mmol kg -1 soil. After 2 wk of incubation, column segmentation and extraction showed that H + moved deeper into the columns on addition of the sulphate salts compared with adding NH 4 H 2 PO 4 or KH 2 PO 4 alone. The maximum depth of P penetration in the columns containing NH 4 H 2 PO 4 was 4.2 cm, while P transport in the columns treated with KH 2 PO 4 was restricted to the top 4.0 cm depth. Addition of (NH 4 ) 2 SO 4 or K 2 SO 4 to NH 4 H 2 PO 4 increased the concentration of water-extractable P by 43 and 21%, respectively, above that in NH 4 H 2 PO 4 alone. Similarly, addition of (NH 4 ) 2 SO 4 or K 2 SO 4 increased the concentration of water-soluble P by 48 and 41%, respectively, above the amount in KH 2 PO 4 alone. The increased water solubility of P on addition of the sulphate salts was attributed to anion competition between HPO 4 2- and SO 4 2- for precipitation with Ca 2+ . We also observed ionic competition between NH 4 + and K + when both cations were added together, causing K + to travel farther into the column and with increased solubility than when applied alone. Our results showed that anion and cation competition can be used to modify the transport and solution concentration of ions through dual banding. These results also suggested that the combination of anion competition by SO 4 2- and pH reduction due to salt effect could have a positive influence on the availability of P in calcareous soils. Key words: Phosphate, sulphate, columns, solubility, diffusive transport, resin
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 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 | 0.001 |
| 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 teacher head, 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".