Ammonium-N Sources Improve the Phosphorus Use Efficiency of Corn.

The source of nitrogenium (N) can affect the phosphorus (P) uptake and use by plants. The aim of this work is to study the impact of different N sources (ammonium-N, nitric-N and both) on the P use efficiency by corn. The experiment was conducted in São Paulo, Brazil, 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 five P doses: 0, 40, 80, 120 and 160 mg kg^-1 like triple superphosphate and four replications. The corn was cutt 40 days after emergence, then dry matter, P accumulation, P concentration, P uptake efficiency, P physiological efficiency and P use efficiency were evaluated. The ammonium-N showed the highest total dry matter production, shoot dry matter production and the best P uptake efficiency and P use efficiency because the presence of NH₄⁺ promote the rizosphere acidification, improve the work of symporters called H+/H₂PO₄- and generates the electrochemical gradient needed for transport of P from the soil solution into the root. The nitric-N showed highest dry matter of roots and highest root/shoot ratio because it is a strategy used to explore more efficiently the soil interstitial spaces when chemical conditions are not favorable, and it means that this N source promote unfavorable conditions for P availability like rizosphere alcalinization. The use of ammonium-N with P fertilizer improve the P use of corn and it can be used like a strategy in P fertilization management.