Nitrogenium Sources and Soil-Root Interactions Affect the Phosphorus Pools.

The source of nitrogenium (N) can change the conditions at root-soil interface, P availability to plants and P levels in different pools. The aim of this work is to study the impact of different N sources (ammonium-N, nitric-N and both) on the different P fractions in rhizosphere and bulk soil. The experiment was conducted in greenhouse and was carried out in pots of 12 L. The treatments consisted of 120 mg kg^-1 of N applied to three N fertilizers (calcium nitrate, ammonium sulfate and the mix of both) combined with triple superphosphate applied in five P doses: 0, 40, 80, 120 and 160 mg kg^-1. The corn was cut 45 days after sowing, then the bulk and rhizosphere soil samples were collected, and P status was evaluated using the sequential fractionation procedure recommended by Heldey et al. (1982) modified by Condron et al. (1985). Ammonium-N showed the highest values of Resin-P in both bulk and rhizosphere soil for all P doses. In rhizosphere soil levels of Resin-P were lower than bulk soil because this available Pi is in solution and is weakly absorbed especially in the zone of root influency. Ammonium-N showed the lowest values of NaHCO₃-Pi and NaHCO₃-Po while Nitrate-N the highest ones because the high Resin-P levels were maintained from these fractions. The lowest values of NaOH-Po and NaOH-Pi fractions by ammonium-N treatment in rhizosphere soil show the ability of this source to improve the plant mechanisms of P mineralization and P availability. The low values of HCl-Pi in all treatments showed an inexpressive participation of P associated with calcium in this soil because it has an acid reaction. The ammonium-P fertilization increase the P availability in the soil.