Season of year effect on response of orchardgrass to N fertilizer in a maritime climate
Bibliographic record
Abstract
This study compared the response of harvests taken in May, June, August and September-October in terms of crop responses (yield, N uptake, and concentrations of crude protein and nitrate) to N fertilizer and residual soil nitrate and ammonium. Three trials were conducted in south coastal British Columbia in 1990–1992 to evaluate the response of an established sward of orchardgrass (Dactylis glomerata L.) to a range of N fertilizer rates. Both yields and daily crop growth rates were highest in cut 1, lowest in cut 4 and intermediate in cuts 2 and 3. For all four cuts, 95 and 90% of maximum yield was attained at about 136 and 82 kg ha-1 of applied N, respectively. Crop N supply from non-fertilizer sources ranged from 36 to 90 kg N ha-1, of which about 52% was attributed to nitrate present in the soil prior to growth and about 48% was N released from the soil, translocated from roots or deposited from the atmosphere. At 95% of maximum yield, crude protein concentrations ranged from 147 g kg-1 in the higher yielding cut 1 to 189 g kg-1 in cuts 2 and 4, while at 90% of maximum yield concentrations were 10 g kg-1 lower in each cut. Plant nitrate concentrations were close to levels that are toxic to cattle for the 95% target yield, but relatively safe at the 90% yield. The crop removed about 50 kg ha-1 more N when fertilized for 95% of maximum yield than for 90%, which translates to over 300 kg ha-1 more crude protein. High relative yield leaves behind more soil nitrate after harvest. The results suggest that the first cut should be managed for 95% of maximum yield with about 130 kg N ha-1. Cuts 2 and 3 should be managed for 90% of maximum yield, to avoid high plant nitrate concentrations, with 100–110 kg N ha-1. Cut 4 should be given no more than 50 kg N ha-1 for less than 90% of maximum yield because of the risk of residual soil nitrates. This study shows for the first time the benefits and disadvantages of applying N at different rates for each harvest over the growing season. Key words: Plant nitrate, nitrogen use efficiency, nitrogen recovery, Dactylis glomerata, relative yield, maximum economic yield
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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) | 0.001 | 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".