Crop Productivity and Nutrient Dynamics in a Shrub (Guiera senegalensis)–Based Farming System of the Sahel
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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.
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