Evaluating the Residual Benefits of Soil Amendments in Reducing Phosphorus Losses to Snowmelt Runoff from Agricultural Fields
Notice bibliographique
Résumé
Phosphorus (P) in snowmelt runoff from agricultural fields across the Canadian prairies is a major source of nutrient pollution to freshwater bodies, such as Lake Winnipeg. The use of soil amendments, such as alum (Al2(SO4)318H2O), gypsum (CaSO4·2H2O), and magnesium-sulphate (MgSO4) have previously shown to reduce P losses from soils with snowmelt in the field, and under simulated snowmelt flooding in the laboratory through converting P to less soluble forms; however, their long-term effectiveness has not been investigated. This thesis examined the effectiveness of alum, gypsum, and magnesium- sulphate after 12 - 18 months after amendment application in (a) reducing dissolved reactive P (DRP) loss with snowmelt runoff in field plots, (b) reducing DRP concentrations in floodwater of intact soil columns with simulated snowmelt flooding, and (c) reducing potential P mobility through changes to P fractions and speciation. Amendments were applied in the fall of 2020 at a rate of 2.5 Mg ha-1 in plots arranged in a randomized complete block design, consisting of 4 replicates of 4 amendments (alum, gypsum, magnesium sulphate, and unamended) for a total of 16 field plots. During the snowmelt period, concentrations of DRP and cations, as well as pH in snowmelt were determined. Using intact soil columns taken from the same field plots, a more controlled laboratory study was conducted, where soil columns were flooded and incubated at 4°C to simulate snowmelt conditions. Porewater and floodwater samples were extracted weekly and analyzed for DRP, cation concentrations, pH, and soil redox potential. Phosphorus species in porewater were predicted using Visual MINTEQ 3.1. on days 0, 28 and 49 during the laboratory study. Phosphorus fractions were also determined using a modified sequential fractionation method. In the field, snowmelt DRP concentrations increased over the sampling period regardless of amendment, with higher concentrations seen after the soil had thawed. In the latter days of sampling, the alum, gypsum, and magnesium sulphate-amendments decreased DRP concentrations in snowmelt by 9 –31% relative to the control. However, differences between treatments and the control were not statistically significant. Snowmelt DRP loads (calculated using DRP concentrations and snowmelt volume) showed a significant positive relationship with snowmelt volume, whereas the relationship with DRP concentration was not significant. During the laboratory study, redox potential in all treatments decreased with time of flooding. Soil columns taken from alum-amended field plots had significantly lower DRP concentrations in porewater when compared to all other treatments, but this effect was not observed for floodwater. Predicted P species showed slight changes in alum-amended soils, suggesting the potential for alum to delay the reductive dissolution of ferric phosphate (strengite, FePO4·2H2O), thereby delaying the P release. However, P fractionation analysis did not show significant differences in soil P fractions between treatments. The results of this research suggest that the effectiveness of these amendments in reducing P loss to snowmelt is very small to negligible one year after application, or after one snowmelt flooding event. This implies that re-application of amendments on a more frequent basis or application at a higher rate may be necessary for amendments to be effective in reducing P loss to snowmelt. However, more field scale research is necessary to provide recommendations to farmers regarding the use of soil amendments for this purpose.
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 | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| 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 ».