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Dossa E.L.,British Petroleum | Diedhiou I.,University Of Thies | Khouma M.,Institute Senegalais Of Recherches Agricoles Isra | Sene M.,Institute Senegalais Of Recherches Agricoles Isra Ceraas | And 6 more authors.
Agronomy Journal | Year: 2012

The indigenous shrub, Guiera senegalensis, coexists with crops to varying degrees in farmers' fields throughout the Sahel, with little known about its biophysical and ecological interactions with soils and crops. Therefore, the objectives were to determine the effect of the presence or absence of shrubs under varying rates of fertilizer on: (i) crop growth and yield, and (ii) soil nutrient dynamics. An experiment from 2004 to 2007 was conducted in northern Senegal where G. senegalensis dominates that had a split-plot factorial design. The presence or absence of G. senegalensis was the main plot and fertilizer rate (0, 0.5, 1 or 1.5 times the recommended N-P-K rate) was the subplot in a peanut (Arachis hypogaea L.)-pearl millet [Pennisetum glaucum (L.) R. Br.] rotation. Averaging over fertilizer rate showed that G. senegalensis had significantly greater crop biomass and yields than no shrub plots (P < 0.05) for all 4 yr. This crop yield response was related to improved nutrient availability (significantly greater for crop N and P uptake in the presence than absence of shrubs in zero fertilizer plots), higher soil quality (elevated particulate organic matter (POM) with shrubs, and a significant correlation of POM with millet yield). Lysimeters below the crop rooting zone had inorganic N levels that were not significantly affected by shrubs compared to no shrub plots, which was attributed to high variability. Combining the ecological potential to restore degraded landscapes with the agronomic benefits demonstrated here, shows that optimized G. senegalensis-crop systems should be further investigated in farmers' fields throughout the Sahel. Copyright © 2012 by the American Society of Agronomy.

Kizito F.,International Water Management Institute | Dragila M.I.,Oregon State University | Sene M.,Institute Senegalais Of Recherches Agricoles Isra Ceraas | Brooks J.R.,US Ecology | And 7 more authors.
Journal of Arid Environments | Year: 2012

Hydraulic redistribution is the process of passive water movement from deeper moist soil to shallower dry soil layers using plant roots as conduits. Results from this study indicate that this phenomenon exists among two shrub species (Guiera senegalensis and Piliostigma reticulatum) that co-exist with annual food crops in Sahelian agro-ecosystems. Real-time measurements were conducted for soil water content, soil water potential and microclimate variables notably; air temperature, relative humidity, wind speed, precipitation and solar irradiance. Additionally, sap flow measurements were conducted in shrub roots using the thermal dissipation technique on intact and coppiced shrubs. Monthly predawn leaf water potential was measured using a portable pressure chamber. Soil water potential (Ψ s) at the 20 cm depth declined significantly during the dry season with diel changes in Ψ s of -0.6 to -1.1 MPa. These variations were attributed to passive water release from shrub roots resulting in overnight rewetting of drier upper soil layers. Sap flow measurements on tap and lateral shrub roots indicated daily reversals in the direction of flow. During the peak of the dry season, both positive (toward shrub) and negative (toward soil) flows were observed in lateral shrub roots with sap flow in the lateral roots frequently negative at night and rapidly becoming positive soon after sunrise. The negative sap flow at night in superficial lateral roots and the periodic positive flow in the descending tap roots were indicative of hydraulic redistribution. Hydraulic redistribution may be an important mechanism for drought stress avoidance while maintaining plant physiological functions in both shrubs and neighboring annuals in water-limited environments. © 2012 Elsevier Ltd.

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