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University of Reading (1996)

Water balance of farmer-managed millet and fallow-savannah on sandy soils in south west Niger

Gaze, Stephen Richard

Titre : Water balance of farmer-managed millet and fallow-savannah on sandy soils in south west Niger

Auteur : Gaze, Stephen Richard.

Université de soutenance : University of Reading

Grade : Doctor of Philosophy (Ph.D.) : 1996

Résumé
Water balance components of a traditionally managed millet field and fallow-savannah field in south west Niger were measured as part of the HAPEX-Sahel experiment. Data were obtained at the 1 to 30 m2 scale, from August 1992 through October 1994, covering 2% wet seasons and 2 dry seasons. Regular measurements were made at both sites of rainfall, soil water content profiles, and soil hydraulic potential profiles. Additional quantitative data collected at the two sites included root length density profiles, microlysimeter measurements of evaporation from the soil surface, and soil textural analysis at selected neutron probe access tube locations. Measurements of plant production at the millet site included above ground dry matter production of the millet, cowpea and weeds. At the fallow site, quantitative plant development data included Guilera senegalensis and herbaceous understorey leaf area development.Field data were characterised by high spatial and temporal variability. In the dry season, 73% of the spatial variability in soil water storage was accounted for by spatial variability in silt+clay content. In the wet season, infiltration was highly spatially variable, ranging from 0.3 to 3.4 times the recorded rainfall for one 60 mm storm at the millet site. Such variable infiltration, combined with spatially variable plant growth resulted in a wet season spatial pattern in soil water storage that was not necessarily related to soil texture. The wet season spatial pattern was highly dependent on the temporal distribution of rain with respect to measurement date. Spatially variable infiltration resulted in spatially variable drainage from the soil profile.Validation of the SWIM (Ross, 1990) simulation model against field data revealed that SWIM did not adequately simulate the measured variability in the point water balance in this environment, and therefore could not be used confidently in a stochastic manner. Consequently, SWIM was used with effective parameters to simulate the deterministic, average water balance at each site for the 3 years.

Annonce : EThOS (UK)

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