Long-term changes in soil phosphorus status related to P budgets under maize monoculture and mineral P fertilization

Monitoring soil phosphorus (P) changes under continuous cropping over decades is an important agronomic and environmental issue. The aim was to determine soil P dynamics in the plough layer as a function of cumulative P budgets (Bcum) across extended cropping periods (7, 12, and 17 yr) for four rates of mineral P fertilization. This field experiment was established in 1975 on a slightly alkaline, sandy loamy soil (luvic Arenosol). Soil P was assessed by three P tests: the concentration of P ions in solution (Cp), Olsen (P(Ol)), and Mehlich-3 P (P(M3)). Annual P budget was calculated as P applied minus P exported by the grain. The Bcum values were the sum of annual P budgets. Bcum, Cp, P(Ol), and P(M3) values were significantly influenced by cropping periods and P rates. The nine combinations (3 periods x 3 soil P tests) of P dynamics versus Bcum were described by linear regressions. For each soil P test, all means fell on the same regression line for the three cropping periods indicating that the P transformation rates were similar for positive and negative P budgets. Relationships depended on soil test P but did not vary for cropping periods. For this specific soil, we calculated that a change in P budget of 100 kg/ha would change Cp, P(Ol), and P(M3) by 0.11 mg/L, 3.3 mg/kg, and 14 mg/kg, respectively. Although this result needs to be confirmed and extended to other soil types, we conclude that a single year of soil sampling after a decade of experimentation would be sufficient to establish the relationship between soil P status and P budgets.