Thermodynamic Limitations to Agricultural Productivity and Food Security: Livestock in Sub-Saharan Africa

By 2050, to feed a nearly tripling and more urbanized population in sub-Saharan Africa (SSA) will require significant increases in crop productivity throughout the region’s agricultural systems, if a greater reliance on imports is to be avoided. Increases in crop yields to maximum potential productivity (closure of crop yield gaps) can produce more calories and protein, but may be insufficient to sustain the burgeoning human population according to recent analysis (van Ittersum et al., 2016). In this thesis, alternative management options (i.e. crop allocation and crop substitutions) are found to increase total energy productivity and the thermodynamic efficiency of food production systems, and provide theoretical potential to support population growth for four SSA countries. Using feeding efficiencies for US livestock systems and accounting for human caloric and protein requirements, the diversion of maize grown explicitly for livestock feed (subsequently referred to as “maize-for-feed”) to direct consumption by humans was found to currently enable population growth by 6 – 11% in Ghana, 4 – 7.4% in Nigeria, 4.4 – 10.5% in Tanzania, and 24.8 – 40.9% in South Africa. By 2050, if crop yield gaps were closed to 80% of potential yields for rainfed maize (by increasing irrigation and nitrogen application) and assuming no increase in harvest area, significantly larger fractions of projected populations were found to be sustained from direct consumption of maize-for-feed, where protein is limiting: 18.4 – 32.2% in Ghana, 11.7 – 21.1% in Nigeria, 6.6 – 15.6% in Tanzania, and 38.1 – 59.5% in South Africa. But when considering energy alone, these amounts are 35 – 42%, 20 – 25%, and 24 – 29% greater, respectively excluding South Africa, than recent projections that include substantial grain-fed livestock, meaning that previous yield gap assessments to identify ‘biophysical limitations’ on agricultural systems may be significant underestimations (van Ittersum et al., 2016). Alternatively, substitution of maize-for-feed with yams, cassava, sorghum, millet, and potatoes was found to also increase population significantly. Cultural practices and socioeconomic conditions affect food demand such as taste preferences and diet composition, but diversification away from grain-fed livestock products with substitution of alternative cropping systems could more efficiently feed people using fewer resources in sub-Saharan Africa. Advisor: Adam J. Lisk