Comments on “No‐Tillage and Soil‐Profile Carbon Sequestration: An On‐Farm Assessment”
Notice bibliographique
Résumé
4 present data on soil organic carbon (SOC) concentrations from soils managed under no-tillage (NT) or plow-tillage (PT) from samples taken from studies of paired fields at 11 (MLRA) sites in three states of the USA. The results seem to show extremely large annual changes in soil organic C stocks between NT and PT to a depth of 60 cm, ranging from +3.75 to −6.65 Mg ha−1 yr−1 (Table 2). However, these values are far greater, and not compatible with, the data displayed in Fig. 2, nor the total stocks of soil N and the C/ N ratio displayed in Tables 3 and 4, respectively. However, the data displayed taken from seven studies in the literature (a total of 16 comparisons) are correctly reported as annual changes. Table 2 should thus be corrected as shown here (Table 1). A further error in the data presentation is in the vertical scale adopted for the Fig. 4, which suggests that most soil profiles contained over 200 Mg C ha−1 to a depth of 60 cm, and that several woodlots showed soil C stocks above 500 Mg C ha−1 to this depth. These errors do not change the main conclusion of the study that “the idea that no-tillage would also enhance soil organic carbon sequestration as an additional benefit of no-tillage technology needs a careful examination.” However the data as presented grossly exaggerate the magnitude of possible gains and losses in such systems. Although the authors cite two studies from southern Brazil, in neither was the soil sampled to a depth >40 cm. Two more recent studies from the same region on the same soil type (Typic Hapludox) were sampled to depths of 100 cm or more (8; 5). In the study of 8 where a N2–fixing legume (hairy vetch—Vicia villosa) was included as a winter crop with maize (Zea mays) in summer, the soil C stocks to 30 cm under NT management was between 5.4 and 9.1 Mg ha−1 greater than under PT. When the soil was sampled to the 100-cm depth the difference in C stocks increased to 16.9 Mg C ha−1 in both rotations. In the study of 5 in two rotations maize was planted in a mixture with either lablab (Lablab purpureum) or pigeon pea (Cajanus cajan). In these rotations, the C stocks to a 17.5-cm depth increased by between 7.9 and 8.4 Mg C ha−1 under NT after a 17-yr period. When sampling was made to 107.5 cm, the increase in soil C stocks under NT were even greater at 13.1 and 21.2 Mg C ha−1 Recent results from sites in the USA (6; 7; 4), as well earlier results from Canada (2; 9), suggest that increases in soil C to depths of 20 to 30 cm under NT do not necessarily indicate that any net C sequestration occurred, as higher concentrations of C can be encountered under PT at depths below this. However, the two studies on free-draining Oxisols in southern Brazil indicate that, (i) C accumulation is highly dependent on N supply (a positive N balance from legumes– 1), and, (ii) in these cases where C accumulation was detected within the “plow layer,” deeper sampling revealed that C sequestration under NT compared with PT was much greater than was to be expected from the shallower soil sampling. Data from all sites indicate that in all sampling to assess net changes in soil C due to changes in tillage practice it is essential to sample well below the plow layer (>60 cm). Most data from temperate regions suggest that superficial sampling will overestimate possible benefits of changes form PT to NT (3), but in the case of deep free-draining soils in the tropics it may be that shallow sampling could lead to gross underestimation of soil C sequestration after adoption of NT.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,007 | 0,031 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,001 |
| Méta-épidémiologie (sens large) | 0,001 | 0,001 |
| Bibliométrie | 0,001 | 0,001 |
| Études des sciences et des technologies | 0,003 | 0,002 |
| Communication savante | 0,002 | 0,002 |
| Science ouverte | 0,003 | 0,002 |
| Intégrité de la recherche | 0,020 | 0,012 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,010 | 0,006 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».