Overcoming phosphorus deficiency in West African pearl millet and sorghum production systems: promising options for crop improvement

Abstract

West Africa (WA) is among the most food insecure regions. Rapid human population
growth and stagnating crop yields greatly contribute to this fact. Poor soil fertility,
especially low plant available phosphorus (P) is constraining food production in the
region. P-fertilizer use in WA is among the lowest in the world due to inaccessibility
and high prices, often unaffordable to resource-poor subsistence farmers. This article
provides an overview of soil P-deficiency in WA and opportunities to overcome it
by exploiting sorghum and pearl millet genetic diversity. The topic is examined from
the perspectives of plant breeding, soil science, plant physiology, plant nutrition,
and agronomy, thereby referring to recent results obtained in a joint interdisciplinary
research project, and reported literature. Specific objectives are to summarize: (1) The
global problem of P scarcity and how it will affect WA farmers; (2) Soil P dynamics
in WA soils; (3) Plant responses to P deficiency; (4) Opportunities to breed for
improved crop adaptation to P-limited conditions; (5) Challenges and trade-offs for
improving sorghum and pearl millet adaptation to low-P conditions in WA; and (6)
Systems approaches to address soil P-deficiency in WA. Sorghum and pearl millet
in WA exhibit highly significant genetic variation for P-uptake efficiency, P-utilization
efficiency, and grain yield under P-limited conditions indicating the possibility of
breeding P-efficient varieties. Direct selection under P-limited conditions was more
efficient than indirect selection under high-P conditions. Combining P-uptake and
P-utilization efficiency is recommendable for WA to avoid further soil mining. Genomic
regions responsible for P-uptake, P-utilization efficiency, and grain yield under low-P
have been identified in WA sorghum and pearl millet, and marker-assisted selection
could be possible once these genomic regions are validated. Developing P-efficient
genotypes may not, however, be a sustainable solution in itself in the long-term
without replenishing the P removed from the system in harvested produce. We therefore propose the use of integrated soil fertility management and systems-oriented management such as enhanced crop-tree-livestock integration incombination with P-use-efficiency improved varieties.Recycling P from animal bones,human excreta and urine are also possible approaches toward a partially closed and efficient P cycle in WA