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Title: Nitrogen and phosphorus runoff losses from variable and constant intensity rainfall simulations on loamy sand under conventional and strip tillage systems

Author
item Franklin, Dorcas
item Truman, Clinton
item Potter, Thomas
item Bosch, David
item Strickland, Timothy
item BENDNARZ, C - UNIVERSITY OF GEORGIA

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2006
Publication Date: 5/7/2007
Citation: Franklin, D.H., Truman, C.C., Potter, T.L., Bosch, D.D., Strickland, T.C., Bendnarz, C.W. 2007. Nitrogen and phosphorus runoff losses from variable and constant intensity rainfall simulations on loamy sand under conventional and strip tillage systems. Journal of Environmental Quality. 36:846-854.

Interpretive Summary: Nutrient losses in runoff may vary between natural rainfall and constant rate rainfall simulations and these variations may be exacerbated by management. Our objective was to quantify effects of natural (variable) rainfall intensity patterns and constant rainfall intensity patterns on nitrogen and phosphorus losses from a loamy sand soil managed under conventional or strip tillage systems. ARS scientists at J. Phil Campbell Sr. Natural Resource Conservation Center, Watkinsville, GA and Southeast Watershed Research Unit, Tifton, GA, in cooperation with Univ. Of Georgia simulated rainfall at a constant and variable rainfall intensity pattern and collected runoff for 70 minutes. No significant differences in total losses were evident for nitrogen and phosphorus in unfiltered samplesfrom either rainfall intensity pattern. This was not the case for filtered samples, in which total mass losses of soluble phosphorus and nitrogen were greatest for strip tillage at a constant rate of rainfall and least for conventional tillage under a variable rate of rainfall. These results indicate that constant intensity rainfall simulations may over estimate the amount of dissolved nutrients lost to the environment in runoff from cropping systems in loamy sand soils. We also found that conservation tillage treatments lost significantly greater amounts of total nitrogen and phosphorus than strip tillage treatments and in contrast, strip tillage treatments lost significantly greater amounts of dissolved phosphorus and nitrogen than conservation tillage treatments. These results indicate that strip tillage systems may be losing more soluble nutrients than conventional tillage systems, but only 33 % of the total nitrogen and 11% of the total phosphorus being lost through over land flow from conventional tillage systems. This information can be used by State Cooperative Extension Systems, USDA-NRCS, environmental consultants, and agricultural producers developing management plans for conservation of financial and environmental resources.

Technical Abstract: Nutrient losses in runoff may vary between natural rainfall and constant rate rainfall simulations. Our objective was to quantify effects of constant (Ic) and variable (Iv) rainfall intensity patterns on N & P losses from a Tifton loamy sand (Plinthic Kandiudult) managed under conventional (CT) or strip-till (ST) systems. We simulated rainfall at a constant intensity and a variable intensity pattern (57 mm hr-1) and collected runoff continuously at 5 min intervals for 70 min. For cumulative runoff at 70 min, no significant differences in total mass losses were evident for TKN-N or TKP-P from either rainfall intensity pattern. In contrast, total cumulative mass losses of dissolved reactive P (DRP) and NO3-N were greatest for ST-Ic, followed by ST-Iv, CT-Ic, and CT-Iv in diminishing order (69 g P ha-1 and 361 g N ha-1;37 g P ha-1 and 133 g N ha-1;3 g P ha-1 and 58 g N ha-1;1 g P ha-1 and 49 g N ha-1). These results indicate that constant rate rainfall simulations may over estimate amount of dissolved nutrients lost in runoff from cropping systems in loamy sand soils. Additionally, CT treatments lost greater amounts of TKN-N and TKP-P than ST treatments and in contrast, ST treatments lost greater amounts of DRP and NO3-N than CT treatments. These results indicate that ST systems may be losing more soluble fractions than CT systems, but only 33% of the total N and 11% of the total P being lost through over land flow from CT systems.