Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2007
Publication Date: 11/20/2007
Citation: Srinivasan, M.S., Kleinman, P.J., Gburek, W., Buob, T. 2007. Hydrology of small field plots used to study phosphorus runoff under simulated rainfall. Journal of Environmental Quality. 36:1833-1842. Interpretive Summary: The National Phosphorus Runoff Project (NPRP) was launched in 1999 to study phosphorus transport characteristics in overland flow from agricultural lands during rainfall periods. Artificial rainfall simulations using rainfall simulators were conducted in small plots (2-m by 1-m) to simulate runoff and P transport. These rainfall-runoff simulations were conducted for three consecutive days. Analyses of data from three such simulations showed that the plots reached an equilibrium condition after the first day of rainfall application. Overland flow and P transport characteristics did not differ significantly on days 2 and 3. Also, the plots produced overland flow as the rate of rainfall applied was greater than the intake capacity of the soils. When dairy manure was surface applied, P transport in overland flow greatly increased as opposed to no-manure conditions. Under such conditions, P transport from these plots was controlled more by surface available P from manure applications than by the overland flow characteristics of the plots.
Technical Abstract: The National Phosphorus Runoff Project (NPRP) uses small plots and rain simulators to assess trends in runoff water quality related to agricultural management. Plot hydrology was analyzed for grassed silt loam (Lewbeach) and sandy loam (Marlow) soils before and after broadcasting dairy manure. Once unamended soils were subjected to an initial rainfall event (5.5 cm for silt loam soil; 9.5 cm for sandy loam soil) to saturate the soil surface, no significant differences in starting moisture conditions, runoff volumes or rainfall depth (events were fixed by runoff duration) were observed over subsequent events. Significant differences were observed in antecedent moisture, runoff amounts and rainfall between soils. Continuous infiltration of rain water during runoff indicated the mechanism of runoff to be that of infiltration-excess. Broadcasting manure resulted in increases in runoff P of at least 10 to 35 fold relative to pre-application runoff. Moisture contents and rainfall depths were significantly greater from manured plots than from unamended plots, but runoff amounts did not differ significantly. Results indicate (1) that rainfall-runoff experiments reach hydrologic equilibrium once surface soils have been sufficiently saturated, and (2) that broadcast manure interacts with rainfall to effect plot hydrology.