|CABRERA, M - UNIVERSITY OF GEORGIA
|CALVERT, V - UNIVERSITY OF GEORGIA
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2003
Publication Date: 12/2/2005
Citation: Franklin, D.H., Cabrera, M.L., Calvert, V.H. 2005. Effects of fertilizer source, surface manipulation and landscape position on runoff volume and quality in grassland plots using simulated rainfall. Soil Science Society of America Journal. 78:84-89.
Interpretive Summary: Producers are under increasing pressure from regulatory agencies and society to reduce the amount of phosphorus and nitrogen leaving agronomic environments to surface waters. Minimizing loss of phosphorus, nitrogen, and water in overland flow from pastures may benefit the producer by improving nutrient use efficiency as well increasing the amount of rainfall captured on-farm. By reducing losses to the environment the likelihood of over enrichment to aquatic systems is reduced. This cooperative work was conducted by researchers from the USDA-ARS, J. Phil Campbell Natural Resource Conservation Center and the Univ. of Georgia to evaluate the effect of fertilizer source, soil aeration and landscape position on runoff volume and quality in pastures. Two phosphorus sources (fertilizer phosphorus and broiler litter) and two mechanical operations (aeration and no aeration) were studied on four landscape positions(shoulder, backslope, footslope, and toeslope)in tall fescue plots. Rainfall was simulated in both April and May 2003, at a rate of 2 in/hr. Runoff samples were analyzed for concentrations of dissolved phosphorus, particulate phosphorus, ammonium and runoff volume. We found that fescue plots fertilized with fertilizer phosphorus lost more phosphorus than plots fertilized with broiler litter. Although aeration had no effect on concentrations of phosphorus and nitrogen losses, it reduced runoff by 27% regardless of fertilization treatment, for the April simulated rainfall. Under drought conditions, capturing an additional 27% of rainfall may improve forage yields. We also found that runoff and phosphorus losses were lower in the footslope position than in other landscape positions. These results support the use of different weighting factors for broiler litter and inorganic phosphorus fertilizer in risk assessment tools used by regulatory (state level environmental), educational (Extension Service), and service (Natural Resource Conservation Service) agencies and suggests that buffer strips placed in the footslope position could further reduce runoff losses.
Technical Abstract: Minimizing the loss of phosphorus, nitrogen, and water in overland flow from pastures may benefit the producer and abate potential eutrophication of aquatic systems. This work was conducted to evaluate the effect of fertilizer source, soil aeration and landscape position on runoff volume and quality in grass. Sixteen tall fescue (Festuca arundinacea Schreb.) plots (1.5 m2) were fertilized (36 kg N ha-1,39 kg P ha-1, 60 kg K ha-1)to provide the recommended rate of P for tall fescue in low soil test P soils. Two P sources (triple superphosphate (TSP) and broiler litter (BL)) and two mechanical operations (aeration and no aeration) were factorially combined to generate four treatments that were applied randomly within each of four landscape blocks (shoulder, backslope, footslope, and toeslope). Runoff samples were collected every five minutes for 30 minutes after initiation of runoff for each of two simulated rainfall events(50 mm/hr for 30 min). Samples were analyzed for concentrations of dissolved reactive phosphorus (DRP), total Kjeldahl phosphorus (TKP), ammonium (NH4)and volume. Fescue plots fertilized with TSP lost (p <.05)more DRP and TKP than plots fertilized with BL (2.9 and 3.44 vs .85 and 1.10 kg P/ha, respectively). Aeration reduced runoff (mm) by 27% (p< 0.16) regardless of fertilization treatment for the April simulated rainfall event. Under drought conditions, gaining an additional 27% water volume to the soil may improve forage yields. No effect of aeration was detected on DRP, TKN or NH4 loss, likely due to high variability. Cumulative runoff, DRP and TKP losses after 30 minutes of runoff were significantly lower (ps < 0.12,0.14 and 0.07, respectfully)in the footslope position than in other landscape positions. These results support the use of different weightng factors for broiler litter and inorganic fertilizer P (TSP) in P-indices and suggest that buffer strips placed in the footslope position could be more effective.