Dissertation/Thesis Abstract

Increasing Indigenous Vegetable Yield and Nutritional Quality through Traditionally- and Scientifically-Informed Soil Fertility Management
by Pincus, Lauren Michelle, Ph.D., University of California, Davis, 2015, 138; 3723701
Abstract (Summary)

Smallholder farms in central Uganda do not reach their agronomic potential in large part due to declining soil fertility. Continuous cultivation and soils that are susceptible to degradation lead to yield declines that threaten household food security. Improvements in soil management are needed to produce both the quantity and quality of food required to reduce food insecurity. However, this requires active farmer participation in the identification and evaluation of different soil management strategies. On-farm and participatory approaches to research were used to evaluate the potential benefits of using Integrated Soil Fertility Management (ISFM) to improve the quantity and nutritional quality of an indigenous vegetable crop, Solanum aethiopicum or nakati, in Uganda's Lake Victoria Crescent. There is increasing recognition of the complementary roles organic and mineral fertilizers play in both short- and long-term soil management. ISFM emphasizes strategically targeted mineral fertilizer use combined with organic inputs to ensure fertilizer use efficiency and crop productivity given the limited availability of all nutrient resources in smallholder systems. Greater yield benefits can be achieved with the combined application of organic and mineral fertilizers compared to either resource applied alone. The ISFM framework also recognizes the influence of social factors on organic and mineral input management. A greater understanding of farmers' soil management decision-making process can guide the development of robust solutions to declining soil fertility.

Yield responses of nakati to organic (composted cow manure) and mineral fertilizers (urea), applied separately and in combination, were measured on farmer-managed plots to evaluate the efficacy of using IFSM on indigenous vegetables. Yield benefits from combined fertility sources were only observed under high fertility application rates with little difference between single or combined sources observed at low fertility rates. Low soil pH led to a significant decline in yields. Yields significantly increased when farmers actively participated in the trials, demonstrating the importance of overall good agronomic practices in achieving yield responses to fertilizer applications.

Measuring the effect of edaphic factors and fertility management strategies on the nutritional value of nakati indicated that uptake of nitrogen and micronutrients were affected primarily by soil pH and fertilizer nitrogen source. Foliar iron and zinc concentrations decreased significantly as soil pH increased, but other soil properties did not affect foliar nutrient concentrations. Foliar nitrogen increased significantly with the use of mineral fertilizer. The practical implications of this are most likely overshadowed when mineral fertilizer applications lead to increasing biomass and foliar nitrogen concentrations are diluted. Smallholder farmers can best attain nutritional benefits from nakati by increasing yields rather than modifying soil environments or fertilizer practices.

A participatory approach was used to document the knowledge and perceptions of farmers regarding their soils and soil management practices. Farmers participated in an ISFM demonstration program where they were exposed to Western scientific soil concepts. Pre-program focus group discussions were used to analyze farmers' existing soil knowledge and perceptions followed by participant observation, post-program interviews and focus group discussions to evaluate if and how scientific soil concepts were assimilated into farmers' soil knowledge. Farmers shared many 'structural similarities' with scientists in how they perceive soil, yet these similarities were often not recognized and utilized when scientists talked to farmers about soil. Thus potentially beneficial technologies, such as the use of mineral fertilizer as part of an ISFM framework, could be at odds with farmers' existing perceptions of fertilizer and remain an underutilized tool in soil fertility management.

Indexing (document details)
Advisor: Scow, Kate
Commitee: Ballard, Heidi, Six, Johan
School: University of California, Davis
Department: Agricultural and Environmental Chemistry
School Location: United States -- California
Source: DAI-B 77/02(E), Dissertation Abstracts International
Subjects: African Studies, Plant sciences, Soil sciences
Keywords: Farmer knowledge, Farmer perceptions, Indigenous vegetables, Integrated soil fertility management, Uganda
Publication Number: 3723701
ISBN: 978-1-339-06588-5
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