Phosphorus use efficiency and long-term trends in soil available phosphorus in wheat production systems with and without nitrogen fertilizer
Bibliographic record
Abstract
Selles, F., Campbell, C. A., Zentner, R. P., Curtin, D., James, D. C. and Basnyat, P. 2011. Phosphorus use efficiency and long-term trends in soil available phosphorus in wheat production systems with and without nitrogen fertilizer. Can. J. Soil Sci. 91: 39–52. Efficient use of phosphorus (P) in crop production is important for economic and environmental reasons, and to prolong the life of a limited resource. Short-term studies often show low recovery of fertilizer P, but P use efficiency may be underestimated because the value of residual P in the soil is ignored. Our objective was to determine fertilizer P use efficiency in two wheat production systems [continuous wheat (CW) and a 3-yr rotation of summer fallow-wheat-wheat (FWW)] using data from a 39-yr study (1967–2005) at Swift Current, SK. Each rotation received either P only (P) or nitrogen plus P (NP) fertilizer. Annual grain P removal was monitored (all straw was returned to the soil) and changes in soil available P (0- to 15-cm layer) were measured by the Olsen bicarbonate method. In 1993, subplots which received no additional P were established to evaluate the residual effect of P fertilizer applied in the preceding 27 yr. Where P was applied each year, grain P removal averaged 54 to 78% of fertilizer P, with values as high as 65 to 109% in 1994 to 2005, the period of lowest water deficit. The P-only treatments removed 13% less P in grain, on average, than NP treatments. In the P-nly systems, Olsen P content increased linearly with time, but in the NP systems it reached a maximum after 20–22 yr and then stabilized. The cumulative P balance (fertilizer P minus P removed in grain) accounted for 60% of the variability in Olsen P accumulation over the course of the experiment. In CW, Olsen P content increased by 0.15 kg ha −1 for each kg ha −1 of P added in excess of crop removal. The rate of Olsen P accumulation was greater (0.20 kg ha −1 for each kg ha −1 of excess fertilizer P) in the FWW rotation possibly due to P mineralization during the summer fallow year. When P was withheld between 1994 and 2005, total grain production in the CW rotation was reduced slightly (by 10%), but there was no significant effect on FWW. Crop P removal (1967–2005) where P was withheld in the final 12 yr was equivalent to 105 and 90% of fertilizer P added to the NP and P-only systems, respectively. We concluded that residual P in prairie soils is retained in forms that are available to plants; wheat crops may therefore recover close to 100% of applied fertilizer P given sufficient time.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| 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".