Phosphorus management is key to effective deployment of root ideotypes in complex soil environments

Purpose We questioned how root ideotypes selected for deep or shallow root architecture function in complex environments with heterogeneous distributions of phosphorus (P), such as in many cropping systems in north-eastern Australia. Methods We used the rhizobox method to evaluate how contrasting genotypes of durum wheat and sorghum (wide and narrow root angle) responded to combinations of starter-P and deep P bands. Results Although we found evidence that root angle may influence spatio-temporal exploration for deep P bands, (early) plant access to P was the critical driver for plant growth. Without P, root system growth was retarded such that genotypic differences were hardly observed. Access to P boosted root exploration at depth by virtue of greater root system size, such that wide-angle genotypes with P outperformed narrow-angle ones without P. Plastic root responses to P benefited the expression of the broader root system architecture. We observed variation between species and individual parameters, but overall Starter-P and deep P bands tended to deliver complementary benefits when considering plant growth, P uptake, and phenological development together. Conclusion Our study highlights that nutritional constraints may limit the ability of root ideotypes to function in complex target environments. Development and deployment of root ideotypes should consider how local conditions (including soil nutrient distribution, physical and biological properties) influence crop phenotype and their ability to deliver the intended benefits. Within this, soil nutrient management is a critical determinant and an opportunity to influence the target environment.