Soil water balance of annual crop-native shrub systems in Senegal's Peanut Basin:: The missing link

Shrubs in the Senegal Peanut basin co-exist with annual food crops in the landscape but are vulnerable to destruction by farmers in a bid to increase agricultural acreage and meet fuel demands. This study determined the impact of two native semi-arid shrub species (Guiera senegalensis and Piliostigma reticulatum) on field water balance components. Soil water fluxes in crop-shrub intercrops and in sole crops were quantified from soil moisture, soil microly-simetery and atmospheric measurements. Up to a depth of 1.10 in, shrubs did not compete with crops for water but preferentially extracted water from the lower portion of the profile below 1.10 in and even beyond the maximum measured depth of 3.5 in. This served as a significant component of the field water balance and was more pronounced at the G. senegalensis site. Shrubs also captured drainage losses beyond the effective root depth of annuals and revealed 25-50% lower deep drainage losses than in sole crop plots. Both shrub species conferred a positive impact on the field moisture regime when intercropped with annuals through enhancing profile recharge in the rainy season. Shrub-mediated effects resulted in 20% higher soil water storage in the upper 1.10 in of the profile in crop-shrub intercrops compared to sole crop control plots. Findings from this study revealed a missing link that deserves special mention. Future work on quantification of water balance in semi-arid regions with crop-shrub associations needs to account for shrub contribution to field moisture fluxes through ground water uptake (G(wup)), a parameter often ignored, yet serves as a vital component in semi-arid ecosystems.