Phosphorus depletion from rhizosphere solution by maize grown in compost-amended soil.

Knowledge of rhizosphere processes is essential for characterizing soil nutrient availability. Our objective in this controlled-climate study was to evaluate phosphorus (P) dynamics in the rhizosphere of juvenile maize (Zea mays L.) grown in soil amended with compost. Maize seedlings were transplanted at the two-leaf stage, and grown for five days. Soil (550 g) collected from the 0-5 cm layer of field plots was placed in one chamber of a vertically divided mini-rhizotron, and soil from the 5-10 cm layer was placed in the other chamber. Micro-suction cups (15 per chamber) were used to collect rhizosphere soil solution that was subsequently analyzed for P and pH. Initially, P concentrations in rhizosphere solution did not differ with distance from the root surface and were similar in the two soil layers. These results reflect the high levels of available P in both soil layers. Solution pH also was similar among the soil layers and distances from the root surface. The soil used in this study was calcareous and strongly buffered against changes in solution pH. After five days, both soil solution P and pH had decreased in both soil layers. However, only soil solution P was affected by distance from the root surface, confirming the pH buffering of the soil. Maize shoot dry matter production was similar in the two soil layers (0.65 g plant-1 in the 0-5 cm layer and 0.60 g plant-1 in the 5-10 cm layer), suggesting that soil P stratification in this soil under no-tillage had little effect on plant growth