Effects of Cover Crops on Soil Aggregate Stability, Total Organic Carbon, and Polysaccharides
Bibliographic record
Abstract
Structural degradation of silt clay loam soils in Delta, British Columbia, has resulted from intensive cultivation of vegetable crops. A field experiment and a laboratory incubation study were conducted to assess the ability of nonleguminous winter cover crops, spring barley ( Hordeum vulgare L.), fall rye ( Secale cereale L.), and annual ryegrass ( Lolium multiflorum Lam.), to affect soil organic C, total and dilute acid extractable polysaccharides, and aggregate stability, expressed as mean weight diameter (MWD). The field experiment included four treatments: three cover crops (spring barley, fall rye, and annual ryegrass) and control (bare soil) arranged in a randomized complete block design. Annual ryegrass and fall rye increased MWD, and all of the cover crops increased soil dilute acid extractable polysaccharides. In the incubation experiment, starch (2.68 g C kg −1 soil) or chopped shoots and coarse roots of fall rye (single‐ [4.14 g C kg −1 soil] and double‐dose [8.28 g C kg −1 soil]) and annual ryegrass (4.62 g C kg −1 soil) were added to a soil from the cover‐crop site and incubated for 2, 4, and 8 wk. Cover crop and starch amendments increased soil organic C, dilute acid–extractable polysaccharides, and soil MWD. After 2‐wk incubation, the starch amendment had the greatest MWD in all the treatments, increasing by 25, 44, and 45%, compared with the annual ryegrass, double‐dose fall rye, and fall rye amendments, respectively ( P < 0.05). After 8‐wk incubation, however, the MWD in the starch amendment containers decreased by 18% compared with that in the double‐dose fall rye amendment treatments ( P < 0.05). All the cover crop amendments increased MWD and percentages of water stable 2‐ to 6‐mm aggregates at all incubation periods ( P < 0.05). Soil aggregate stability highly correlated with dilute acid‐extractable polysaccharides in the field and in incubation experiments. This study suggests that the dilute acid‐extractable polysaccharide fraction represents active binding agents under short‐term cover crops. It has been shown that soil aggregate stability can be increased under 8‐mo nonleguminous cover crops in the intensively cultivated soils.
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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".