Nitrogen pools and processes in agricultural systems of Coastal British Columbia — A review of published research
Notice bibliographique
Résumé
A significant amount of research on nitrogen (N) dynamics has been conducted within the past 20 yr in south coastal British Columbia. This succinct set of data has practical and environmental information on N cycling particularly focusing on gains to and losses from agricultural fields, and transformations of soil N pools. Coastal British Columbia fields have received large annual additions by application of fertilizer and manure. Some of the manure N from animals using locally grown forages is recycled within the farm operation, but a large amount of N is imported as feed especially for intensive animal production. Budget calculations estimated that there may be substantial losses of N through volatilization from manure, particularly from housing and storage areas, and during application to fields. Some of the volatilized ammonia in holding areas may be recycled to fields via precipitation. Direct measurements of these losses and returns of N have not been made. Studies have shown that there is limited risk of leaching of nitrate beyond the root zone during the growing season because most of the annual rainfall occurs over the winter and because nitrate can be adsorbed to soil particles. However, any extractable inorganic N (nitrate directly and ammonium after nitrification) in the profile at the end of the growing season will be lost over the winter. Most of that loss is due to nitrate leaching, but conditions are also favorable for denitrification. There is considerable (> 200 mg N k−1 in some soils) ammonium-N fixed in Fraser Valley soils, but the impact of this phenomenon to crop growth is still poorly understood. Wetting and drying cycles have a great influence on the dynamics of this pool of soil N. The response of spring growth of grass to the time of N application was influenced by the relative competitiveness of microorganisms and plants for available soil N. A study comparing short-season (broccoli) and long-season (sweet corn) crop responses to N applications showed that the rate at which the plants require N influences their response to N amendments. Raspberries were found to require relatively small quantities of N on a land area basis because of the wide inter-row distances. An autumn soil nitrate test has been proposed for making fertilizer N recommendations for raspberries. Although knowledge gained from this research has provided a basis for interpreting studies for the development of N management practices and for making interim recommendations, a method to predict the amount of N mineralized from soil organic matter is key to the development of soil-analysis-based N rate recommendations. Key words: N cycling, nitrate, ammonium, fixed ammonium, soil organic N, mineralization
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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 | 0,001 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,009 | 0,017 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| Communication savante | 0,003 | 0,001 |
| Science ouverte | 0,001 | 0,001 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 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 ».