Tuesday, 11 July 2006 - 11:25 AM

Dryland Conservation Technologies for the Restoration of the Productive Capacity and the Conservation of Crust Prone Soils in the Sahel.

A. Mando, IFDC, Boulevard de la Kara, Lomé, Togo and Robert B. Zougmoré, Institute for Environment and Agricultural Research (INERA), INERA, Ouagadougou, 04 POB 8645, Burkina Faso.

Erratic rainfall, nutrient depletion, gradual loss of structure, hardpan formation and crusting, which lead to severe water and soil losses through runoff, are major Sahelian agricultural constraints. The main consequences are the occurrence of frequent dry spells, the decline in vegetation cover that lead to the extension of bear and crusted soils. In order to improve crop production in this region, soil management techniques need to address both water and nutrient constraints. However, due to the lack of financial resources to acquire fertilizers, and to the limited availability of organic resources, the introduction of techniques that minimize the use of external inputs and that are cheap and easily accessible will certainly increase their chance of adoption by most farmers. This paper shows how traditional soil management practices can combat land degradation and improve productivity. The methods consist in rehabilitating crusted soils that were abandoned as wastelands, by supplying only limited external inputs in small pits (zaï) or large ones (half-moons) dug to capture runoff water. Mainly through biological processes, these practices improve soil moisture, soil structure, soil fertility (decomposition and nutrient release), and reduce soil resistance to root penetration, resulting into a great impact on crop performance under semi-arid conditions. Several studies conducted in the region are very much informative: In semi-arid Niger, it was found that the annual mean runoff coefficient was about 6 to 10 times lower on zaï plots compared to control plots. As a result of increased infiltration, there is an increase in water availability for crop growth. In Burkina Faso, research studies on the zaï technique reported that control plots and zaï pits alone resulted in similar grain (0.2 t ha-1) and biomass production (0.9 t kg ha-1), suggesting that under the semi-arid conditions, lack of water was not the sole limiting factor, but also nutrients. The addition of neem leaves increased yield (0.4 t ha-1) and biomass (1.9 t ha-1) production, as well as the application of compost (0.7 t ha-1 of grain and 2.8 t ha-1 of biomass). Combined application of compost or manure with mineral fertilization (N±P) in the zaï pits improved significantly cereal production (1.7 t ha-1 of grain and 5.3 t ha-1 of biomass). These studies also reported a significant development of several vegetation species after two years of zaï application, thus showing the potential of this practice to regenerate vegetation. The half-moon collects great amounts of water that considerably improves soil water storage, making this technique well-adapted to Sahelian zones. In semi-arid Burkina Faso, half-moons pits with animal manure or compost produced sorghum grain yields ranging from 0.9─1.6 t ha-1 .The half-moon pit without any external input produced only 0.04 t ha-1 of grain. Several studies also indicated that half-moon technique with application of organic and mineral sources of nutrients induces a 4- to 10-fold increase of crop yields. Zaï and half-moon techniques with appropriate nutrient management are effective methods for the rehabilitation of degraded soil productivity, therefore could contribute reducing food insecurity and human pressure on the arable lands in the Sahel.

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