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For the study of field wind erosion, detailed observations of windblown sediment transport in the field are needed. The objective of this study was to determine the best method to quantify the mass of wind-blown material moving past a fixed point during four storms. Twenty-one Modified Wilson and Cooke (MWAC) sediment catchers were installed in a pearl millet [Pennisetum glaucum (L.) R. Br.] field in the Sahelian zone of Niger, on a sandy, siliceous, isohyperthermic Psammentic Paleustalf. Each catcher trapped materials at seven heights between 0.05 and 1.00 m. The vertical profiles of measured horizontal mass fluxes were described by two different models, a three-parameter power function and a live-parameter combined model, which is combination of an exponential function and a power function. For all four storms, both models described accurately the mass fluxes between 0.05 and 0.26 m, but fitted mass fluxes at 0.50, 0.75, and 1.00 m deviated from measured fluxes. Deviations were 21.1, 45.2, and 60.6% for the power function and 12.4, 18.5, and 38.0% for the combined model. Mass transport rates were calculated by integrating the mass flux profiles across height. The differences in calculated mass transport rates were small, but because of the better fit, the combined model was preferred. Correcting for the trapping efficiency of the MWAC catchers (0.49) and multiplying by the storm duration resulted in total mass transport values, which are equal to the mass of soil passing a strip of 1-m width perpendicular to the mean wind direction. The average mass transport values were 102.7, 15.5, 31.8, and 149.8 kg m -1 , respectively, for the four storms.

In northern Burkina Faso (West Africa), a study was undertaken to explore the possibilities of restoring the infiltration capacity of crusted soils through the stimulation of termite activity. Treatments consisted of the application of a mulch of a mixture of wood and straw without insecticides (resulting in “termite plots”) and the application of the same mulch and an insecticide (Dursban with chloropyrifos as the active ingredient) to prevent termite activity (resulting in “non-termite plots”). Three rainfall simulations of 60 minutes duration with an intensity of 50 mm/h at an interval of 24 hours between the first and the second and 72 hours between the second and third simulation were applied, to study the effect of consecutive showers on termite-modified soil characteristics. Cumulative infiltration amounts, final infiltration rates, soil water content and porosity were larger and bulk density was smaller on termite plots as compared to non-termite plots. This suggests that termites may be an important agent in soil-crust control and in the improvement of soil physical properties in Sahelian ecosystems.

This paper deals with the effect of rainfall on the process of wind erosion of beach sands and presents results from both field and wind tunnel experiments. Although sediment transport by splash is of secondary importance on coastal dunes, splash-saltation processes can move sediments in conditions where no motion is predicted by aeolian processes. The effect of raindrop impact on the movement of soil particles by wind was measured on a sand beach plain using an acoustic sediment sampler. In general, an increase of particle movement by wind at the sensor heights was observed during rainfall. Rainfall also affected the wind erosion process during and after rain by changing the cohesive conditions of the surface. The influence of the surface moisture content on the initiation of wind erosion and on the vertical distribution of transported sand particles was studied in a wind tunnel. Moisture significantly increased threshold wind velocities for the initiation of sediment transport and modified vertical sediment profiles.

This paper sets out that the dynamics of the Sahelian rangeland vegetation can be interpreted as a cusp catastrophe and that this interpretation offers a promising basis for the description and analysis of tbis ecosystem. Firstly, an existing scheme of the dynamics of Sahelian herbaceous vegetation is translated into the state-and-transition formulation. Secondly, the application of the cusp catastrophe is explored by studying the behaviour of the Sahelian rangeland ecosystem under changing effective rainfall and grazing inteusity, using the transitions from the state-and-transition formulation as vectors along the cusp manifold. This conceptual cusp catastrophe model subsequently results in the identification of hypotheses and the detection of 5 catastrophic properties of this ecosystem (biiodality, inaccessibiity, sudden jumps, divergence and hysteresis) that have important management implications. The continuous and the discontinuous processes occurring in the Sahelian rangeland ecosystem can both be captured in a tified conceptual model by applying the cusp catastrophe theory. Testing the hypotheses generated by the conceptual model and searching for additional catastrophic properties, such as divergence of linear response and critical slowing down, is a useful direction for future research

Hedgerows of Cassia siamea were planted 4 m apart in a maize/cowpea rotation on a 14% slope of a Lixisol/Alfisol in 1988 at Machakos, Kenya. Infiltration rates were measured in situ across hedgerow barriers with a drip infiltrometer. During the dry season the steady infiltration rate under the hedgerows was 135 mm h −1 while on the alleys in between it was 41–49 mm h −1 and on the control plot 39–48 mm h −1 . Corresponding values for the wet season were 69 mm h −1 for the hedge and 8–11 mm h −1 for the alley. Removal of the hedge plants revealed that much of the increase is due to significantly more macropores in the topsoil beneath the hedgerow than in the topsoil beneath the alley. Differences in pore size distribution in the subsoil were small and not significant. Total increase in average infiltration rate of the hedgerow barrier system in the dry season is 30% and in the wet season is 94% as compared to the alley. The combined effect of above- and below-ground changes makes hedgerow barriers valuable for runoff control.

As hardly any data can be found on the water requirement and yield response to water of Aloe vera, an irrigation experiment on transplanted aloe poles was conducted on the Caribbean island of Aruba. Compared to non-irrigated treatments irrigation shows a positive influence on growth, number of developed leaves, raw gel figure and gel production per plant. The amount of irrigation water to apply can be best calculated based on crop coefficients (Kc) between 0.20 and 0.30. Treatment based on a Kc value higher than 0.30 did not further increase production. A lysimeter study conducted over a relatively short period revealed that the crop coefficient for Aloe vera varied between 0.25 and 0.40 which is characteristic of the so-called agave/pineapple group.

This article discusses irrigation technology in relation to the concept of sustainabi‐lity. For sustainable agricultural development, farmers should have control over irrigation technology; they have to be social carriers of technology. Five social variables of technology are defined: product, organization, financial capacity, access and knowledge. Farmers will act as social carriers if these variables match their social situation. The contribution made to sustainable agriculture by flood irrigation and introduced small‐scale pump irrigation technology is evaluated using these five variables.