Exploring Root Traits for Efficient Early Nutrient Uptake of Sorghum (Sorghum bicolor L.) Genotypes Grown under Soil Moisture Stressed and Nutrient Limited Soils: A Root Chamber Experiment

Extreme drought condition is a serious challenge for agricultural production and is threatening food security in sub-Saharan countries. Plant rooting system has a considerable role in ensuring crop yield under nutrient-depleted soils and extreme weather events. For instance, a narrow root angle has been suggested to improve sorghum yield in drought regions. A higher root number and root hair density have also been proposed for nutrient acquisition under low soil fertility. Drought coupled with nutrient depletion is the most limiting abiotic factor which reduces crop production in the sub-Saharan region. Hence, there is still a need for knowledge to elucidate which root traits are important in optimizing nutrient uptake at low soil fertility and moisture stress environments. This thesis investigated the variations in root length, root angle, and root intensity among sorghum genotypes and their relationship to phosphorous (P) uptake under different soil nutrient and moisture status. Accordingly, twenty sorghum genotypes were selected, and the treatments were arranged in a split-split plot design. Significant genetic variability was found between the root traits (P<0.0001) and P uptake (P<0.0001). Nutrient application and a higher moisture level increased shoot biomass and P uptake (P<0.01) but had a limited effect on the root traits. Long root enhanced P uptake under low soil nutrient availability and moisture-stress environments (R2 = 0.194; p = 0.03). A wider root angle also ensured efficient P uptake, particularly under high soil nutrient and moisture levels. Unlike the expectation, root intensity had a limited effect on P uptake, irrespective of soil nutrient and moisture status. The findings of this thesis demonstrated the functional links between root traits and P uptake under various soil nutrient and moisture levels. Thus, genotype selection using root traits could be one of the breeding strategies to optimize P utilization in drought environments and low-input cropping systems.