Date of this Version
Long–term manure and fertilizer applications to a soil can increase phosphorus (P) and nitrogen (N) transport in runoff. This study was conducted to determine P and N transport in runoff following long–term (since 1953) manure and fertilizer applications. Duplicate soil samples (32) were collected in 1998 from the top 0.1 m of selected plots of a long–term manure and fertilizer applications field experiment and later placed in 1 m2 soil pans in the laboratory. Manure and fertilizer were mixed with 16 of the soil samples, while no treatment was applied to the other half (long–term residual effect). Simulated rainfall was then applied to the soil during initial and wet (24 hours later) events.
Manure added just before simulated rainfall resulted in significantly greater concentrations of dissolved P (DP), bioavailable P (BAP), particulate P (PP), total P (TP), NO3–N, and NH4–N than when the last manure application was the previous year in 1997. Soil test P level was not a significant factor in DP loss when manure was applied just before rainfall. When the last manure application was the previous year, similar concentrations of DP, BAP, PP, and TP were measured on the manure and no–manure treatments. Concentrations of NO3–N and NH4–N in runoff were not influenced by long–term fertilizer application, but significantly increased with increasing N application rate when N was applied just before rainfall. Phosphorus concentration in runoff decreased with time of runoff up to 45 minutes, after which the P concentration remained constant. NO3–N and total N concentrations continued to decrease for the entire runoff period. Manure and fertilizer should not be applied when the probability of rainfall immediately following application is great.