Ph.D. Candidate Nate Bogie successfully defended his dissertation in front of a full house of fellow graduate students and faculty.
Beneficial Hydrologic Relations Between Food Crops and Native Evergreen Woody Shrubs in the Peanut Basin, Senegal
by Nate Bogie
PhD candidate, Environmental Systems
Advisor: Prof. Teamrat A. Ghezzehei
SE2 Rm. 302
Friday, October 7, 2016
The Sudano-Sahel is prone to frequent shortages of food supply. Agricultural productivity in this region is severely limited by drought stress as a consequence of variable rainfall patterns as well as soil degradation. Farming practices that provide adequate nutrient and water supplies while maintaining crop yields and land conservation are urgently needed in the region. Local knowledge and prior research indicate that intercropping with the native woody shrubs Guiera senegalensis and Piliostigma reticulatum has a great potential to increase crop yields and avert drought-induced crop-failures. The goal of this study is to provide quantitative and mechanistic understanding of the effect of the native shrubs on water and nutrient availability to crops, and how the crops respond to being grown near shrubs. This research shows that shrubs help protect shallow soil layers early in the season from potentially deadly drought and heat stress and despite lower soil moisture content at the end of the season, crops grown in association with shrubs have increased biomass production and a faster development cycle. Under irrigation an isotopic tracer study investigating upward hydraulic redistribution by the shrubs and subsequent uptake of the water by crops was carried out. Tracer signal was found in the crops of all three plots which strongly supports the existence of vertical hydraulic redistribution and transfer of water from the shrubs to the crops under drought conditions. Soils near the shrubs had lower hydraulic conductivity and surface infiltration rates than the soils under the sole crop plots and there were no significant differences in water retention between the two soils. By keeping the rhizosphere hydrated, hydraulic redistribution by the shrubs may be one way that shrubs can help crop roots avoid xylem cavitation and heat stress related mortality under drought conditions. Using even the limited resources that farmers possess, this agroforestry technique can be expanded over wide swaths of the Sahel.
Nate graduated from UC Santa Cruz in 2006 with a BS in Earth Sciences. He joined the group of Professor Teamrat A. Ghezzehei at UCM in 2011 to study plant-water relations in the Senegalese Sahel as part of the NSF-PIRE Senegal project. After his dissertation he will pursue a career in research.