Timing of water use and phosphorus exploitation strategies are promising key traits of Sorghum to maintain biomass and yield production under resource limitations

<title>Abstract</title> Aims Limited access to nutrients and water is leading to yield losses in smallholder farming systems in semi-arid regions. Therefore, crop rotations including legumes as well as utilizing drought-tolerant sorghum varieties might be a strategy to improve access to scarce resources. Methods Two early and five late maturing sorghum genotypes were tested to identify stress adaptation traits to water and phosphorus limitations in combination with or without ¹⁵N labelled legume pre-crops on a phenotyping platform. Results Lower soil P content significantly delayed the time of flowering of all genotypes compared to higher P content, however organic residues could reduce this effect. ¹⁵N recovery in sorghum biomass proved the use of pre-crop root residue N in all treatments, although there was only a beneficial pre-crop effect on sorghum biomass and yield under sufficient water supply. Mycorrhizal infection was relevant for plant nutrition at anthesis under low P and showed a positive correlation with ¹⁵N recovery and root P content. Drought had the major impact on yield. Early maturing genotypes, with the highest reduction in shoot biomass and adapted transpiration prior flowering, could maintain yield production. Conclusions A promising trait combination for nutrient-poor soils in semi-arid areas with high drought risk, seemed to be early-maturing varieties with a high root to shoot ratio, rapid AMF establishment and low transpration (normalized to leaf area T_n) – in this study realized in the early maturing genotype Grinkan. Such genotypes save water prior flowering and reduce their post flowering water stress in combination to their P uptake withstanding low soil availability.