Soil phosphorus status in potato fields

Potato crops generally require high amounts of phosphorus (P) fertilizer to reach economically acceptable yields. However, high inputs of P not only increase production cost, but also may increase the environmental risk of P runoff. We evaluated soil test P and sequentially-extracted P in soil samples from 10 potato fields which had three-year crop rotations with or without irrigation. Whereas soil test (Olsen) P was not significantly influenced by crop rotation and irrigation, P levels in sequentially-extracted fractions were impacted by management. The impact of crop rotation was mainly expressed on water extractable P. Irrigation had greater influence on stable P extracted in NaOH and HCl fractions. Higher levels of NaOH extractable inorganic P were observed in soil from irrigated fields, while higher levels of HCl extractable P were observed insoils under rainfed management. Our data indicate that crop management practice may eventually affect P availability and runoff potential in these potato soils over the long term.However, more field data from longer experimental periods are needed to confirm this hypothesis.