Nutrient concentrations and NH4+-N mineralization under different soil types and fallow forms in southern Cameroon

To evaluate the soil‐fertility sustainability of the fallow systems, nutrient concentrations and NH4+‐N mineralization were determined in different soil and fallow types in the humid forest zone of southern Cameroon. Two experiments were conducted, the first comprised planted leguminous tree Calliandra calothyrsus, planted leguminous Pueraria phaseoloides, and regrowth mainly composed of Chromolaena odorata on the Typic Kandiudult. The second experiment made up of a fallow dominated by C. odorata, a fallow with C. odorata removed, and a P. phaseoloides fallow on the Rhodic Kandiudult, Typic Kandiudult, and Typic Kandiudox. In the first experiment, available P, Ca2+, K+ concentrations and effective CEC under C. calothyrsus were, respectively, 40%, 22%, 45%, and 15% lower when compared to P. phaseoloides but no differences were found between soils under P. phaseoloides and C. odorata. Mineralization of NH4+‐N was higher under C. calothyrsus than under C. odorata‐ and P. phaseoloides‐fallow types, indicating the impoverishment of organic material under the former. In the second experiment, the beneficial effect of P. phaseoloides was found in the Rhodic Kandiudult in the 0–10 cm layer throughout its low NH4+ release from mineralization. In the Typic Kandiudult, no differences in NH4+‐N mineralization were found between C. odorata and P. phaseoloides fallows. In the Typic Kandiudox, there was no difference in NH4+ mineralization between the three fallow types. According to the nutrient concentrations and NH4+ mineralization, the fertility sustainability of the different fallow types may be ranked as follow: P. phaseoloides ≥ C. odorata > C. calothyrsus > fallow without C. odorata. Nährstoff‐Gehalte und NH4+‐Mineralisation unter verschiedenen Bodentypen und Bracheformen in Süd‐Kamerun Nährstoffgehalte und NH4+‐Mineralisationsraten wurden bei verschiedenen Bodentypen und Bracheformen in der humiden Waldzone in Südkamerun untersucht, um die Nachhaltigkeit dieser Brachesysteme zu beurteilen. Es wurden zwei Experimente durchgeführt. Das erste Experiment erfolgte an der gepflanzten baumartigen Leguminose Calliandra, der ebenfalls gepflanzten krautigen Leguminose Pueraria und der natürlich vorkommenden krautigen Chromolaena als Brachen auf sandigem Boden. Das zweite Experiment setzte sich zusammen aus natürlicher Brache, hauptsächlich bewachsen mit Chromolaena, natürlicher Brache, wobei Chromolaena entfernt wurde, und Pueraria‐Brache auf sandigem Lehmboden sowie sand