P-31 NMR Characterization of Fertilizer Residual P In Cotton/Corn Fields.

Phosphorus (P) is an essential plant nutrient.  However, over application of P to soils has raised concerns because excess P in runoff could result in eutrophication of fresh water bodies. A field experiment of poultry litter (PL) and chemical fertilizer (CF) to a Cecil soil used for cotton and corn production has been maintained for 10 years. In the top soil (0-2.5 cm), the soil total P levels in fields with conventional tillage (CT) were about 50% of those with no-till (NT) managements for both PL and CF application. Sodium hydroxide (0. 25M NaOH)-EDTA (0.05 M) extracted 63 to 82% of soil total P. The extraction efficiency was consistently higher with PL than CF under the same managements and soil layers. Solution P-31 NMR data revealed that, whereas a significant part of P in PL was in the organic forms, the relative abundance of organic P (% of total P) was lower in these soils with PL than in corresponding soil with inorganic P fertilizer (CF). Phytate, the major organic P form of PL, was not accumulated in PL-applied soils as the abundance of phytate in those soils was similar to that of CF-applied soils. This suggests either the dynamic transformation of phytate in these cotton/corn fields, with phytate available as a plant nutrient; or loss of phytate in leaching or runoff, which is and environmental concern.