Nitrogen mineralization under summer fallow and continuous wheat in the semiarid Canadian prairie
Notice bibliographique
Résumé
The ability of soils to provide a portion of the N required by crops via N mineralization of organic matter is of economic and environmental importance. Over a 40-yr period (1967–2006), soil NO3-N and plant-N measurements were made under summer fallow and in systems cropped to spring wheat (Triticum aestivum L.), on a medium-textured Orthic Brown Chernozem (Aridic Haploboroll), at Swift Current, Saskatchewan. These values were used to estimate net N mineralization (Nmin). Each year, above-ground plant N was measured at harvest and soil NO3-N was measured before seeding, soon after harvest, and just prior to freeze-up in October. Also, in the first 18 yr of this study NO3-N and above-ground plant N were measured eight times between spring and fall in selected treatments; these data were used to make a more detailed estimate of Nmin. In a third experiment, conducted on the same soil at a nearby site in 1975, many small lysimeters were sampled six times between spring and harvest of spring wheat. We used this lysimeter study to assess the effect of N fertilizer rate and soilwater on net Nmin. Results from the more frequent sampling were more plausible than those from sampling at three different times per year. On average, net Nmin in the 20-mo summer fallow period was about 118 kg ha-1 (15 kg ha-1 between harvest and the first spring, 93 kg ha-1 between the first spring and second fall, and 10 kg ha-1 between the second fall and seeding). The average net Nmin under a wheat crop between spring and fall was between 53 and 63kg ha-1. Net Nmin increased with water, but excessive water appeared to reduce apparent net Nmin, probably due to leaching and denitrification losses of N, which were not assessed in our estimation of Nmin. Regression analysis was used to show a positive association between net Nmin and precipitation, between spring and fall, for most of the systems examined. There was evidence that tillage promotes N mineralization. At normal rates of N fertilizer (i.e., < 100 kg ha-1), fertilizer had no effect on Nmin. Net Nmin was directly proportional to fallow frequency, averaging 68, 83, and 90 kg ha-1 yr-1 for continuous wheat, fallow-wheat-wheat, and fallow-wheat rotations, respectively. Although our results may only be applicable to medium-textured soils of similar organic matter content in the Brown and Dark Brown Chernozemic soil zone, they provide data and information against which process-based models can be tested. They also provide useful first approximations of Nmin measured under field conditions where few long-term data currently exist. Key words: N mineralization, plant-N, fertilizer-N, crop rotation, irrigation, tillage
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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 | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,002 |
| Études des sciences et des technologies | 0,002 | 0,001 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,001 | 0,001 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
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 ».