Nitrate leaching in the semiarid prairie : Effect of cropping frequency, crop type, and fertilizer after 37 years
Bibliographic record
Abstract
A high NO3 concentration in drinking water can be a health hazard. Further, leached N represents an economic loss to the producer. Although NO3 leaching to ground water would be minimal on the semiarid prairies, leaching can occur especially where frequent summer fallowing is practiced. We used a crop rotation study, initiated in 1967 on a medium-textured Orthic Brown Chernozem, at Swift Current, Saskatchewan, to determine the influences of fallow frequency, crop types, and fertilizer on nitrate leaching after 37 yr. Nitrate distribution was measured to 4.5 m depth by 0.3-m increments, in 10 cropping systems in fall 2003. We deduced that some NO3 leached beyond the rooting depth (1.2 m) of spring wheat (Triticum aetivium L.), especially under a fallow-wheat rotation receiving N and P fertilizer. The amounts of NO3 leached tended to be greater and to be located deeper in the soil profile as fallow frequency increased (e.g., fallow-wheat > fallow-wheat-wheat > continuous wheat, all receiving N and P fertilizer based on soil test). However, in this semiarid environment, NO3 leaching was not great, being highest under fallow-wheat (N + P) (180 kg N ha-1 leached in 37 yr). In fallow-containing systems inadequate fertilizer N or P resulted in reduced crop growth and N uptake leading to a tendency for greater leaching of the NO3 (about 145 kg N ha-1 in 37 yr) mineralized during the fallow period than when such a system received N and P based on soil tests (about 66 kg N ha-1 leached in 37 yr). In continuously cropped treatments there was little evidence of leaching. Replacing wheat grown on fallow with the shallow-rooted flax (Linum usitatissimum L.) in a fallowwheat-wheat (N + P) rotation resulted in greater NO3 leaching in the flax system (156 vs. 66 kg N ha-1 ) due to less N uptake by flax. In contrast, when the wheat grown on fallow was replaced with fall rye (Secale cereale L.) there was no leaching, perhaps because the fallow period was much shorter (12 mo compared with 20 mo for spring wheat) and also because the fall-seeded crop used soil NO3 in the fall and early spring reducing opportunities for leaching. Key words: Wheat, flax, fall rye, lentil, cropping frequency
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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 | 0.001 |
| 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".