Coupling phosphate type and placement promotes maize growth and phosphorus uptake by altering root properties and rhizosphere processes

Context: Nutrient distribution and phosphate fertilizers can impact maize growth, but how to match the type of phosphate fertilizer and the application method to enhance root-foraging capacity for phosphorus (P) is unclear.Objective: This study was aimed at characterizing the effects of different phosphate fertilizers and placements on maize growth, grain yield, root properties and rhizosphere processes on calcareous soil. Methods: A soil column experiment with five different phosphate fertilizers [single superphosphate (SSP), monoammonium phosphate (MAP), diammonium phosphate (DAP), urea phosphate (UP) and ammonium pol-yphosphate (APP)] applied either uniformly or locally 10-20 cm deep in a greenhouse. In addition, a 2-year field experiment with five P fertilizer treatments (non-fertilization and broadcast MAP, DAP, UP or APP) was conducted.Results: In the soil column experiment, localized application of SSP, MAP, UP and APP significantly promoted the growth and P uptake of maize by modifying the root morphology. Localized application of each P fertilizer increased (by up to 74 %) the first-order lateral root density and first-order lateral root length of maize in the fertilizerenriched layer, resulting in a significant increase in the efficiency of root P acquisition by maize. In the field experiment, the rhizosphere pH of maize supplied with MAP, UP or APP was reduced by 0.5-0.7 units in comparison to DAP in 2018. Compared with MAP and DAP, application of UP or APP in the field did not show significantly improve maize growth and P uptake.Conclusions: These results show that optimizing P fertilizer types and placement modified root morphology and physiology, and consequently promoted maize growth and P accumulation, but further characterization of the localized application of different P fertilizers in the field is needed. Significance: Engineering root properties and rhizosphere processes by manipulating fertilizer types and place-ment improves fertilizer-use efficiency and reduces environmental footprint of food production.