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Accueil du site → Doctorat → États-Unis → 1993 → Soil genesis, classification, and nitrogen cycling in forest ecosystems of the northwestern Rif region of Morocco

Oregon State University (1993)

Soil genesis, classification, and nitrogen cycling in forest ecosystems of the northwestern Rif region of Morocco

Ben Jelloun, Hassane

Titre : Soil genesis, classification, and nitrogen cycling in forest ecosystems of the northwestern Rif region of Morocco

Auteur : Ben Jelloun, Hassane

Université de soutenance : Oregon State University

Grade : Doctor of Philosophy (PhD) 1993

Résumé
Soil-related information is lacking in the forest ecosystems of the Rif region. Detailed soil descriptions, and chemical, physical, and mineralogical information are necessary for planning and management. Soils of the forested area around Chefchaouen, Morocco, were described along altitudinal gradients, and classified using soil taxonomy. Nitrogen mineralization was measured in the laboratory, using anaerobic and aerobic incubations, and in the field with trenched plots. The dominant forest species were Quercus suber, Quercus perinalca, Abies marocana, Pinus pinaster var. moghrebiana, Pinus radiata, and Cedrus atlantica. Most of the soils were shallow, unstable, and were limited in their productive capability. They were classified as Entisols, Inceptisols, Mollisols, Alfisols, and Ultisols. The main soil development processes were weathering, decalcification, melanization, mineralization, humification, rubifaction, leaching, lessivage, gleization, and erosion. There were some differences in clay minerals related to parent material.
The potentially available soil nitrogen, limin from anaerobic incubation and No from aerobic incubation, in the survey experiment did not show significant differences among sites, because of the large within-site variability. Ninth ranged from 22 to 87 mg-N kg’ in the mineral surface horizons and from 3 to 31 mg-N kg’ in the subsurface horizons. No ranged from 48 to 143 mg-N kg" and from 18 to 57 mg-N kg’ in the upper and lower horizons respectively. The rate constant of N mineralization (k) ranged from 0.130 to 0.253 week’ in the surface horizon and decreased significantly with depth. The values of Npan and No measured in trenched plot experiment were lower than those measured in the survey experiment. Nran ranged from 11 to 46 mg-N kg’ and No from 29 to 54 mg-N kg’, with a significant decrease with depth for both. Yearly net N mineralization measured in the field varied from 6 to 29 kg-N ha’ yr’ in the surface soil (ranging from 0-10 to 0-40 cm), and from 9 to 14 kg-N ha’ yr’ in the subsurface horizon (ranging from 10 to 70 cm). Yearly net N uptake by plants was highly correlated with net N mineralization and varied from 17 to 25 kg-N ha’ yr’.

Mots clés : Forest soils — Morocco — Rif Mountains Forest ecology

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