LONG–TERM MANURE AND FERTILIZER APPLICATION EFFECTS ON PHOSPHORUS AND NITROGEN IN RUNOFF

Abstract

Longterm manure and fertilizer applications to a soil can increase phosphorus (P) and nitrogen (N) transportin runoff. This study was conducted to determine P and N transport in runoff following longterm (since 1953) manure andfertilizer applications. Duplicate soil samples (32) were collected in 1998 from the top 0.1 m of selected plots of a longtermmanure and fertilizer applications field experiment and later placed in 1 m 2 soil pans in the laboratory. Manure and fertilizerwere mixed with 16 of the soil samples, while no treatment was applied to the other half (longterm residual effect). Simulatedrainfall was then applied to the soil during initial and wet (24 hours later) events.<br><br>Manure added just before simulated rainfall resulted in significantly greater concentrations of dissolved P (DP),bioavailable P (BAP), particulate P (PP), total P (TP), NO3N, and NH4N than when the last manure application was theprevious 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 onthe manure and nomanure treatments. Concentrations of NO3N and NH4N in runoff were not influenced by longtermfertilizer 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 remainedconstant. NO3N and total N concentrations continued to decrease for the entire runoff period. Manure and fertilizer shouldnot be applied when the probability of rainfall immediately following application is great.