2013 Annual Report
Under the terms of this agreement, the ARS will develop the RUSLE2D DLL version of RUSLE2, develop code for calculating ephemeral gully erosion and develop code to track soil organic carbon/matter in agricultural systems. The priority of the items will be set by a NRCS National Agronomist. The ARS agrees to follow the direction of the NRCS, National Water Erosion Specialist Agreement Contact. The National Water Erosion Specialist will be the primary, day-to-day RUSLE2 contact who will communicate with the ARS development team.
The implementation of this project was delayed. The budget was only posted and made available on 06/09/2013. Nevertheless, progress was made on the objectives.
The current RUSLE2 DLL including the most up-to-date science code has been supported. Extensive testing has found no problems by DLL users from Purdue, Wisconsin, Department of Energy (DOE), NRCS, and Agren, Inc.
The RUSLE2 code was adapted to make use of the Rothemsted carbon model(ROTH-C) approach to modeling carbon sequestration in the soil. This included linkage of the existing RUSLE biomass decomposition routines in place of the first stage of the ROTH-C equations. This has been implemented for 24 1-inch layers in a soil profile. This method appears to work well, but will require some calibration of the approach to adequately represent various land uses and soil moisture effects. Efforts are underway to determine how to link the cropping factor or Soil Tillage Intensity Rating (STIR) to the decomposition factor in ROTH-C. Preliminary tests show that modification of the way RUSLE2 “sifts” residue during tillage will be needed to reproduce soil carbon maxima near the soil surface. This modification of RUSLE2 residue burial behavior will be implemented and evaluated in the future.
The Ephemeral Gully Erosion Estimator (EphGEE) computes ephemeral gully evolution for a series of storm events that are predicted by RUSLE2, although it may be driven by other models. The model has been implemented as an independent C++ program, which has as inputs a series of extensible markup language (xml) files containing a map of potential gullies, soil properties, sediment size definition, and spatially-distributed runoff and sediment loads to for a series of storm events. Erosion is computed based on erosion rate determined as a function of local excess shear stress. Gully channels evolve according to Foster and Lane’s (1983) approach, which assumes gully channels evolve in a two-step process, first eroding vertically to form a rectangular channel whose width is proportional to flow parameters, and once a layer of high resistance is reached, channels widen at varying rates. This is the same conceptual approach taken in Chemicals, Runoff and Erosion from Agricultural Management Systems (CREAMS) and the watershed version of the Water Erosion Prediction Program (WEPP). Currently, EphGEE is a standalone model to which RUSLE2 outputs are passed through a Geographic Information System (GIS) interface. The user must specify the soil erodibility and critical shear stress parameters. The code has been adapted for implementation within RUSLE2, however at present there is no user interface exists that would allow users to define the channel properties. The issue of defining channel erodibility and critical shear stress from the National Soil Information System (NASIS) soils database also remains to be resolved. These issues are beyond the scope of the current statement of work.
ARS is preparing a new release that will include the new grazing subroutines and NRCS printing templates. An NRCS release is anticipated in 2013. Developing installers and fixing bugs found in this new release will be major efforts supported by this project which will be extended for an anticipated period of at least six months, considering the very late start date when funds became available (June 2013).