Depletion of Rhizosphere Solution Phosphorus by Corn Grown in Compost-Amended Soil Under No-till Production.

Knowledge of rhizosphere processes is essential for characterizing soil nutrient availability. The objective of this controlled-climate study was to evaluate phosphorus (P) dynamics in the rhizosphere of juvenile corn (Zea mays L.) grown in soil with and without compost amendment. Undisturbed blocks of soil (2-cm width by 33 cm depth) were collected from plots that had been under no-till production since 1988. Annual compost application (6 Mg C ha^-1) began in 1998, and changed to a P removal basis in 2004. Soil blocks were placed in two-chamber mini-rhizotrons, corn seedlings were transplanted at the two-leaf stage, and grown for ten days. Micro-suction cups (15 per chamber) were used to collect rhizosphere soil solution that was subsequently analyzed for P and pH. Corn shoot dry matter production was two-fold greater in the compost amended soil (1.43 g plant^-1 vs. 0.75 g plant^-1). Phosphorus concentrations in rhizosphere solution did not differ with distance from the root surface, but were significantly higher in the compost-amended soil. Soil solution P and pH decreased with time in both soils; however, only soil solution P was affected by distance from the root surface, confirming the pH buffering of the soil. Our results suggest that compost amendment can increase soil P availability, thus providing an alternative to fertilizer P input, which will help sustain the global supply of mineral P.