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NITROGEN DYNAMICS AND ENZYMATIC ACTIVITES OF SHRUB-MILLET SYSTEMS IN SENEGAL

DeLay, Chelsea
http://rave.ohiolink.edu/etdc/view?acc_num=osu1483456670733017

Abstract Details

2017, Master of Science, Ohio State University, Environment and Natural Resources.
Rapid population growth in sub-Saharan Africa has prompted unsustainable agricultural practices such as over-grazing and intensive cropping. This has led to a drastic decrease in soil quality. Generally the soils in this region have high sand content and poor biomass productivity, making maintenance of soil organic matter difficult. However, the continuous decline of soil organic matter is a major driver of the severe degradation processes observed. Indeed, agricultural methods that maintain a quality soil environment while sustaining crop yields are desperately needed. The Sahel is commonly managed as a parkland agroforestry system, where trees and shrubs randomly grow and establish in farmers’ fields. Research has found that woody shrubs in arid and semi-arid environments can create “resource islands” by accumulating nutrients and organic matter underneath and around the shrub canopy. Specifically, there are two native shrub species, Guiera senegalensis and Piliostigma reticulatum, found in Senegal and throughout much of the Sahel that are known to increase yields when intercropped with pearl millet (Pennisetum glaucum) and peanut (Arachis hypogaea). Research has provided evidence of both species performing hydraulic redistribution, the movement of water from tap roots to surface roots that is caused by a water potential gradient from wet subsoil to the dry soil surface. Rainfall is a major limiting factor for crop growth in the Sahel, so this hydraulic redistribution process can have substantial impacts on crop growth and microbial activity surrounding the shrub in times of drought. An increase in microbial activity has major implications regarding nutrient cycling and decomposition in the soil. Therefore, one of the objectives of this study was to investigate soil enzyme activities in the presence and absence of G. senegalensis across a rainfall gradient in farmers’ fields of Senegal over the course of two growing seasons. ß-glucosidase, acid phosphatase, and ß-glucosaminidase activities were positively affected by the presence of shrubs. This shrub effect was observed even during a year with decreased rainfall, suggesting that hydraulic redistribution was supporting microbial processes when rainfall was scarce. The shrub has significant effects on soil chemical properties, with total C and N significantly greater underneath the shrub canopy than away from the canopy across all sampling locations and years. Certain secondary macro- and micronutrients were also elevated in the presence of G. senegalensis. These results suggest that the increased concentrations of nutrients and hydraulic redistribution associated with these shrubs are supporting a larger and more active microbial community than the surrounding xeric soil. Consequently, the second objective of the study was to determine if the shrub rhizospheres are stimulating N fixation by harboring a larger population of diazotrophs. This experiment took place at two long-term research sites in Senegal. Soil samples were collected from millet plus shrub plots and millet alone plots at various sampling dates and 15N incubations were set up to determine %15N incorporation. Samples collected from the shrub plots revealed higher amounts of incorporation compared to the no shrub plots. However, only P. reticulatum exhibited a statistically significant increase in 15N incorporation. Furthermore, samples collected within the influence of both shrub species revealed a slight, but statistically insignificant increase in incorporation during the dry season. These results suggest that hydraulic redistribution is sustaining microbial communities capable of performing N fixation throughout the dry season. Results from both experiments provide evidence that these shrub systems have significant impacts on microbial activity and biogeochemical processes that can lead to higher agricultural productivity.
Richard Dick (Advisor)
Warren Dick (Committee Member)
Olli Tuovinen (Committee Member)
124 p.
Agriculture; Agronomy; Microbiology; Soil Sciences
Soil; shrubs; Guiera senegalensis; Piliostigma reticulatum; Senegal; enzymes; Nitrogen; microbiology

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Citations

  • DeLay, C. (2017). NITROGEN DYNAMICS AND ENZYMATIC ACTIVITES OF SHRUB-MILLET SYSTEMS IN SENEGAL [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483456670733017

    APA Style (7th edition)

  • DeLay, Chelsea. NITROGEN DYNAMICS AND ENZYMATIC ACTIVITES OF SHRUB-MILLET SYSTEMS IN SENEGAL. 2017. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1483456670733017.

    MLA Style (8th edition)

  • DeLay, Chelsea. "NITROGEN DYNAMICS AND ENZYMATIC ACTIVITES OF SHRUB-MILLET SYSTEMS IN SENEGAL." Master's thesis, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483456670733017

    Chicago Manual of Style (17th edition)

osu1483456670733017
469
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