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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.

The contribution of Cassia siamea hedgerows and mulch to erosion control was evaluated on a 14% slope of a Lixisol/Alfisol at Machakos, Kenya. The four treatments, in 400 m 2 runoff-plots were: hedgerows with prunings applied as mulch to the crop, hedgerows and crops with prunings removed, mulch only applied to the crop and a control. The hedgerows were planted on the contour, 4 m apart and 0.25 m between plants. Maize and cowpea were planted in sequence. The control plot sustained an average annual water loss over 3 y of 31 mm runoff and soil loss of 19 t ha −1 . The best treatment, hedgerows with mulch, reduced losses to 13% and 2% of the control. Hedgerows without mulch reduced losses respectively to 23% and 7%, while mulch without hedgerows reduced losses to 41% and 17%. Soil loss was considerably influenced by one single storm in April 1990 due to the nature of that storm and to the susceptibility of the soil to erosion at that particular time. Differences in crop yield between treatments were small. The hedgerow treatments depressed cowpea yield slightly in less than normal rainy seasons but improved cowpea yields in wet seasons.

A method to calculate the statistical distribution of a scaling factor from soil-water retention curves consists of measuring the particle-size distribution by laser scattering, computing soil water retention curves using the Arya and Paris model, and calculating a scale factor for each function. The method was tested by comparing measured and predicted soil-water retention curves. The advantage of this method is in its simplicity and ease of use. The applicability of the method to a given soil texture depends on the verification of the calculated soil-water retention functions.

In a recent article (Diemont et al., 1991) about erosion on Java, it has been postulated that low inputs, not surface erosion, is the main cause of low productivity of upland food crops on this island. In this article it is argued that this hypothesis is too simple. An analysis of empirical field data about the effect of erosion on crop productivity indicates that the effects of erosion and agronomic inputs are confounded. Erosion causes farmers to apply low inputs because only limited returns can be expected on eroded lands. The relations between erosion and crop productivity are site specific; the extent and quality of conservation measures and intensity of agronomic inputs varies per soil type.

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 paper deals with the effect of the Thomson weir and weirbox on measured recession curves. Small discharges can be measured accurately with a Thomson weir. The variation of the flow rate entering the weirbox changes the storage in the box, which thus gives a time lag in the measured discharge. Three cases of inflow were investigated: zero inflow, exponential recession inflow, and linear recession inflow, as predicted by the Zarmi model. Exponential and linear recession were described by differential equations, solved numerically through a predictor-corrector method. In most cases the time lag is less than 1 min but at very low discharges the time lag can become important. The results presented indicate that the modifying effects of the weirboxes on the outflows from these catchments are not sufficient to explain the differences between the observed exponential recessions and the linear recessions predicted by the Zarmi model.

The irrigation schemes of the villages Gande and Gallade in the Bakel Department in Senegal are managed by a farmer association and an agency. The agency had to install, repair and maintain motorpumps, assist in the lay-out of canals, structures and parcels, and to provide fuel and other inputs on credit. Associations had to manage the irrigation systems and repay the agency in time and in proportion to amounts of inputs received.

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.