Hydrological Modelling of Zaï Planting Pit

An estimated 23.5 % of global land area is affected by land degradation and this has resulted in 1 to 2.3 million hectares of agricultural land becoming unsuitable for cultivation. Situated in the Sudano-Sahelian zone, Niger is a landlocked area, experiencing the challenges of severe soil crisis in a context of water scarcity.

To reverse the trend of land degradation in Niger, many sustainable land management practices are used, including rainwater harvesting techniques. So far, few studies consider the potentials of in situ rainwater harvesting in the establishment of agroforestry systems on degraded lands. The objective of this study was therefore to evaluate the biophysical viability of the forestry zaï technique (a water harvesting technique used to reclaim degraded lands) in the Sudano-Sahelian zone of Niger under current and future climatic conditions. A two-year field experiment was conducted on a degraded land in Niger using a randomized block design with four replications. The treatments included the traditional planting technique and the forestry zaï technique. Compared to the traditional planting technique, the forestry zaï increased the soil water storage in the root zone which in turn led to a significant improvement of millet grain yield that reached 1088 kg.ha-1, compared to 668 kg ha-1 recorded under the traditional planting technique.

In contrast to millet, A. senegal showed mild sensitivity to the water harvesting technique, while tree survival rate was 100 % for the traditional and zai systems. The study also revealed that the technique of the forestry zaï is a suitable rainwater harvesting technique even under changing climatic conditions. Therefore, it contributes both to adaptation (a solution to water scarcity and land degradation) and mitigation (carbon sink) for perennial tree species.