Tillage - fertilizer changes: Effect on some soil quality attributes under long-term crop rotations in a thin Black Chernozem
Bibliographic record
Abstract
A crop rotation experiment initiated in 1958 on a thin Black Chernozemic clay at Indian Head, Saskatchewan, was managed using conventional tillage until 1989 and changed to zero-tillage in 1990. We soil sampled in 1987 and 1997 to determine management effects on selected soil biochemical characteristics, and the change in some of the more labile soil quality attributes relative to the change in soil organic C and total N. Rotations examined were: fallow-wheat (Triticum aestivum L.) (F-W), fallow-wheat-wheat (F-W-W), continuous wheat (Cont W), legume green manure (GM)-W-W, and F-W-W-hay (legume-grass)-hay-hay (F-W-W-H-H-H). The monoculture cereal rotations were either fertilized with N and P based on soil tests or unfertilized, while the legume-containing systems were unfertilized. There was also a F-W-W (N + P) treatment, in which about 20% of the straw was harvested each crop year. With the change to zero-tillage management in 1990 and in anticipation of greater soil water storage, higher rates of N were added thereafter. This resulted in an upward trend in stubble-crop yields and a positive yield response of wheat grown on fallow, where before the change wheat grown on fallow did not respond to fertilizer. The corresponding increase in crop residue production and residue C inputs resulted in all fertilized systems gaining organic C and total N in the 0- to 15-cm depth between 1987 and 1997, while the unfertilized systems remained unchanged. Soil organic C and total N, microbial biomass C (MBC), light fraction organic C and N (LFC and LFN), mineralizable N (N min ) and wet aggregate stability (WAS), generally had positive responses to fertilization, to increased cropping frequency, and to the inclusion of legume green manure or legume hay crops in cereal-based rotations. Straw harvesting did not influence grain yields, nor did it influence the soil biochemical characteristics, though it tended to render the soil more prone to erosion. Response to cropping frequency was apparent only in the fertilized systems, where the more labile soil quality attributes, (i.e., MBC, LFC, LFN, and N min ) were more sensitive than organic C or total N. However, gains in LFC and MBC in response to fertilizer did not account for a significant fraction of the gain in total organic C. During the period 1987 to 1997, MBC in the 0- to 15-cm depth increased by 40% in absolute value and by 33% relative to organic C (3.6% of organic C in 1997 vs. 2.7% in 1987). The same was true for LFN in the fertilized treatments and in the green manured system (1.46% of total N in 1997 vs. 1.15% in 1987). However, LFC hardly changed over this period. Relative to total N, N min decreased in 1997 compared with 1987, likely due to higher immobilization. Wet aggregate stability was generally greater in 1997 compared with 1991, reflecting greater crop residue inputs and less soil disturbance under zero-tillage management. Key words: Microbial biomass, Light fraction C and N, aggregate stability, Mineralizable N, yields
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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".