Haruhiko Horino

Direct Observation Of Soil Water Movement Through Soil Macropores Using Soft X-rays And Stereographing

Water movement in soil was observed directly and recorded on videotape using soft X-ray technology with a liquid contrast agent and on continuous photos. The movement of soil water occurred in an Andosol sample, and quantitative analyses were carried out by image processing. The results shown here are:The fluids flowing in tubular macro pores connected with each other. The flow showed spatial motion in which the tubular pores were sometimes swollen. Soil water moved into small pores like a volcanic explosion and also moved, worm-like, according to the shape of the tubular pores. Soil water movement occurred only in some tubular pores. In most cases, soil water was not detected in the pores.The spatial structures of macropores shown in three-dimensional graphics were drawn from stereo-radiographs, based on the observation of the spatial contribution of soil pore structures and the calculation of their actual length and tortuousity.Applying Darcy’s law, various permeabilities (K2, K3, K4) of the soil were calculated using the diameters of the dominant macropores and actual velocities. The permeability was compared with the permeability (K1) tested independently by the constant head method. Differences among K1, K2, K3 and K4 were not significant.The validity of Darcy’s law was tested using the constant head tank at different heads and samples. Results show that the validity of Darcy’s law was not confirmed.The Reynolds number was calculated using the actual diameter of the tubular pores and velocities of the agent measured by the stereo-graph obtained by the video. The flow seemed to be transitional between laminar and turbulent.

Re-evaluating Indigenous Technologies for Sustainable Soil and Water Management in the Sahel: A Case Study from Niger

West African Sahel relies much of its food production on rain-fed pearl millet cultivation (Pennisetum glaucum (L.) R. Br.). Its productivity is physically constrained by irregular rainfall and the inherent poor nutrient holding capacity of the soil. Extensive and deprival nature of its agriculture was sustained by migrant and semi-nomadic lifestyle of people in the older days (Charlick 1991). However, a great increase of population in the last five decades caused overexploitation of land resources and reduced resilience of the system. Due to erosion and nutrition deficiency, productivity of pearl millet has declined. Today the old paradigm of extensive agriculture is no longer valid for sustainable land management.