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Ohio State University (2017)

The Role of Shrub Agroforestry Systems in Increasing Food Security for the West African Sahel

Bright, Matthew Burton Hall

Titre : The Role of Shrub Agroforestry Systems in Increasing Food Security for the West African Sahel

Auteur : Bright, Matthew Burton Hall

Université de soutenance : Ohio State University

Grade : Doctor of Philosophy (PhD) 2017

Résumé partiel
The West African Sahel (WAS) faces environmental and socioeconomic constraints that routinely threaten regional food security. Subsistence farmers must contend with drought, low soil fertility, and land degradation while sustaining livelihoods from rainfed agriculture without the aid of synthetic fertilizers and pesticides. Rapid population growth and climate change only exacerbate the challenges. Consequently, the WAS urgently needs scientifically-validated, sustainable agricultural systems to guarantee landscape conservation, to provide sufficient nutrient and water supplies, and to optimize crop productivity. A truly effective system for combating food insecurity, however, requires the adoption of local, low-cost inputs that simultaneously increase yields and coexist within the framework of the socio-economic and environmental demands of the region. This dissertation, therefore, examined the use of a ubiquitous and increasing component of the natural savanna ecosystem in the WAS – shrubs – to enhance the growth and yields of the staple crops, pearl millet (Pennisetum glaucum) and groundnut (Arachis hypogeae). The first research chapter (Chapter 2) investigated the long-term (eleven years) effect of a dominant, semi-evergreen shrub, Piliostigma reticulatum, on yields, soil fertility, soil carbon, and nutrient cycling at an experimental site in southern Senegal. The density of P. reticulatum was increased to 1000 shrubs ha-1 in a split-plot factorial design with the presence or absence of shrubs as the main plot and different rates of fertilizer as the subplot. Millet and groundnut were planted in a yearly rotation. The results showed a strong positive effect of P. reticultaum on millet water use efficiency, yields, and soil nutrients. The results also clearly demonstrated that this cropping system promotes C sequestration. Furthermore, the study showed, surprisingly, that the shrubs use water from the previous year’s rainy season for the following year’s growth which helps explain why P. reticulatum does not compete with crops for limited water. Chapter 3 studied the long-term (twelve years) effect of another dominant shrub, Guiera senegalensis, to increase the soil quality, growth, and yields of millet and groundnut using the same experimental design as found in Chapter 2 (1500 shrubs ha-1) but at a site in central Senegal with extremely sandy, degraded soils. The results unequivocally demonstrated that G. senegalensis could maintain yields and improve soil quality through limited rainfall. The mechanisms behind the shrub effect were examined more closely in this chapter : its effect on soil water content, temperature, and root growth between plants. There was a temporal offset between growth of G. senegalensis and millet roots. G. senegalensis primarily grew during the dry season, whereas millet grew during the rainy season which again shows why shrubs and crops do not compete for limited nutrients.


Page publiée le 26 décembre 2018