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Due to increased population pressure and limited availability of fertile land, farmers on desert fringes increasingly rely on marginal land for agricultural production, which they have learned to rehabilitate with different technologies for soils and water conservation. One such method is the indigenous zai technique used in the Sahel. It combines water harvesting and targeted application of organic amendments by the use of small pits dug into the hardened soil. To study the resource use efficiency of this technique, experiments were conducted 1999-2000, on-station at ICRISAT in Niger, and on-farm at two locations on degraded lands. On-station, the effect of application rate of millet straw and cattle manure on millet dry matter production was studied. On-farm, the effects of organic amendment type (millet straw and cattle manure, at the rate of 300 g per plant) and water harvesting (with and without water harvesting) on millet grain yield, dry matter production, and water use were studied. First, the comparison of zai vs. flat planting, both unamended, resulted in a 3-to 4-fold (in one case, even 19-fold) increase in grain yield on-farm in both years, which points to the yield effects of improved water harvesting in the zai alone. Zai improved the water use efficiency by a factor of about 2. The yields increased further with the application of organic amendments. Manure resulted in 2-68 times better grain yields than no amendment and 2-7 times better grain yields than millet straw (higher on the more degraded soils). Millet dry matter produced per unit of manure N or K was higher than that of millet straw, a tendency that was similar for all rates of application. Zai improved nutrient uptake in the range of 43-64% for N, 50-87% for P and 58-66% for K. Zai increased grain yield produced per unit N (8 vs. 5 kg kg À1 ) and K (10 vs. 6 kg kg À1 ) compared to flat; so is the effect of cattle manure compared to millet straw (9 vs. 4 kg kg À1 , and 14 vs. 3 kg kg À1 ), respectively, Therefore zai shows a good potential for increasing agronomic efficiency and nutrient use efficiency. Increasing the rate of cattle manure application from 1 to 3 t ha À1 increased the yield by 115% TDM, but increasing the manure application rate further from 3 to 5 t ha À1 only gave an additional 12% yield increase, which shows that optimum application rates are around 3t ha À1 .

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In the West African Sahel, few direct measurements are currently available for the major land-use types on the extent of soil losses by wind erosion. A measurement campaign was therefore carried out in 1997 to monitor windblown sediment fluxes using Big Spring Number Eight (BSNE) sand-traps in a conventionally managed cultivated field and bush fallow in western Niger. Sediment balances were derived from the measured windblown sediment mass fluxes. Results indicate that sediment fluxes in a cultivated field increased linearly over distances up to 76 m irrespective of wind speed and duration. Sediment deposition over distances up to 47 m in an adjacent bush fallow was well described by an exponential decay function with a near constant trapping efficiency coefficient of 0.11 m À 1 for incoming sediment mass fluxes between 10 and 45 kg m À1. Soil mass balances up to À17.5 and +10.5 Mg ha À1 were measured in a single storm in the field and fallow, respectively. However, 89% of the sediment deposition observed in the fallow occurred within the first 20 m. The nutrient content of windblown sediment generally declined with distance into the field and increased with distance into the bush fallow. Because of the low nutrient content of the native soil, total nutrient losses remained very low (<163 mg m À2 for any given nutrient). However, such losses were by no means negligible compared to the average nutrient uptake by a millet crop. The present measurements confirm that wind erosion can result in substantial soil losses in traditionally managed fields on the sandy soil of the Sahel. The bulk of sediment transport is, however, predominantly short range as the saltating material is efficiently trapped by the natural vegetation of fallow land.