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Kyoto University (2014)

Dynamics of Soil Organic Matter under Slash-and-Burn Agriculture in a Semiarid Woodland of Zambia

Ando, Kaori

Titre : Dynamics of Soil Organic Matter under Slash-and-Burn Agriculture in a Semiarid Woodland of Zambia

Auteur : Ando, Kaori

Université de soutenance : Kyoto University

Grade : Doctoral Thesis 2014

Sommaire partiel
In Eastern Province, Zambia, the spots unburned and burned with emergent and bush tree piles could be present simultaneously within the cleared field after burning. The different extent of burned biomass (emergent and bush tree piles) brought the different fire intensity which affected soil organic matter (SOM) degradation and nutrient release. The fire intensity was significantly higher at spots burned with emergent tree piles in terms of maximum temperature and duration of burning. With increase in fire intensity, SOM was degraded by soil heating and C and N contents of SOM decreased. Especially labile fraction of SOM such as coarse organic matter (COM ; > 2000 µm) and particulate organic matter (POM ; 53–2000 µm), composed of plant detritus in various stages of decomposition, was degraded by burning. The degradation of SOM and microbial mortality brought the increase in available nutrients such as NH4–N, available P, and exchangeable K and Ca with an increase in fire intensity. As a result, maize grain yield increased with fire intensity, which was also attributed to limited weed biomass by soil heating. Thus, the recent decrease in emergent trees brought high spatial variability of fire intensity inside the cleared field, which caused high spatial variability of the amount of SOM, especially for labile SOM fraction and available nutrients. Because more areas are being burned with bush trees owing to the decrease in emergent trees, grain yield may decrease, although the severe decrease in SOM may be alleviated.

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