Preferential Leaching of Water and Chloride in a Clay Loam Soil as Affected by Tillage and Rainfall Intensity
Notice bibliographique
Résumé
Abstract There is a concern that preferential flow (i.e., bypass of soil matrix) of water and chemicals through soil macropores may enhance leaching below the root zone of agricultural crops, which may impact groundwater quality. Our objective was to investigate the nature of preferential flow in a clay loam soil and to ascertain the potential impact of tillage practice and rainfall intensity. We utilized a long-term (since 1968) conventional tillage (heavy-duty cultivator) and no-till field located at Lethbridge in southern Alberta. Four large (46 x 46 x 51 cm) undisturbed soil blocks were excavated from each tillage field (unreplicated) during the fallow phase of a wheat-fallow rotation. The soil blocks were transported to the laboratory, stored under drying conditions (32 months), and rainfall-leaching experiments conducted under unsaturated, transient conditions. In the laboratory, we attached a funnel-lysimeter consisting of 64 square funnels or cells to the bottom of each block. Three rainfall experiments were conducted on each block and a solid chloride tracer was applied to the top of the soil block before each rainfall event. Blocks were at a soil water content of field capacity prior to each rainfall. A total of 22 mm of rainfall was applied in 60, 30 and 15 min, corresponding to rainfall intensities of 22, 44 and 88 mm h-1, respectively. The volume of water outflow and concentration of chloride in each cell was determined after each rainfall event. Water outflow through >98% of cells indicated that many soil pores contributed to leaching of water. Convex-shaped curves of cumulative water outflow from cells versus cumulative area indicated non-uniform water flow, but the degree of water flow preference was low. Semi-variograms of cell water outflow indicated random flow, and the pattern of cell water outflow was stable with time and among rainfall intensities. Chloride outflow in <14% of cells indicated that only a few soil pores contributed to leaching of chloride. Total mass loss of chloride from each soil block was <0.1% of the total amount applied, which suggested most chloride was retained within the soil block, and was more consistent with immobile water rather than anion exclusion. Tillage practice seemed to exert a stronger influence on water outflow parameters than rainfall intensity, with a trend towards greater preferential flow of water under CT than NT. Total block water outflow increased with greater rainfall intensity for CT, and to a lesser extent for NT. Mean values of maximum chloride concentration were higher for CT than NT at 88 mm h-1, but not at the two lower intensities. Rainfall intensity had no effect on mean values of maximum chloride concentration for either CT or NT. Our results indicated that although preferential leaching occurred in these wet clay loam soils under relatively high rainfall intensities, the amount of chloride leached past 50 cm was minimal. Caution is advised in extrapolating these results to scenarios where conditions are different from this study.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,003 | 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 | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 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 tête enseignante, 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 ».