Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2012
Publication Date: 3/26/2012
Publication URL: http://handle.nal.usda.gov/10113/54169
Citation: Dabney, S.M., Yoder, D.C. 2012. Improved descriptions of herbaceous perennial growth and residue creation for RUSLE2. Agronomy Journal. 104(3):771-784. Interpretive Summary: New methods were developed to make it easier to realistically determine erosion from hay and grazing lands. Trained specialists describe vegetations using easily understood parameters, such as the expected total forage production level and the monthly distribution of growth. An underlying plant growth model then determines the effects of alternative harvest management on the amount of forage harvested, the amount of above and below ground residues returned to the soil, and the resulting soil erosion caused by rainfall. The USDA-NRCS is developing extensive databases based on this new technology that will soon be implemented nationally. After the implementation of the new model and the new databases, conservationists using RUSLE2 will be able to consider erosion estimates as part of the forage/grazing planning process. Using the new procedures, hay and grazing lands will receive appropriate recognition for their contribution to soil and water conservation.
Technical Abstract: The methods commonly used in earlier versions of RUSLE and in other resource management modeling tools calculate residue production only in response to operations or during periods of canopy decline, but these methods result in underestimation of residue amounts and overestimation of soil erosion from pasture and hay lands. To solve this problem, new vegetation routines were implemented in RUSLE2 that better reflect the amount of residue added by perennial vegetation during its growth, and that make it is easier to model haying/grazing scenarios. The new routines are based on the assumption that all unharvested above ground biomass growth will die after its life span is reached, and that biomass will be added to a standing residue pool. Users specify the characteristics of a vegetation assemblage in terms of total annual potential production under good management, monthly production percentages reflecting expected fertility and irrigation levels, the average vegetation lifespans, maximum canopy height, the cutting height for optimal yield, and the tendency of the vegetation to thicken (form a sod) in response to repeated defoliations. The users then specify actual harvest management and an underlying model predicts plant growth responses in terms of the amount of forage harvested and the amount of above and below ground residues returned to the soil. The USDA-NRCS is developing extensive databases so that the new version of RUSLE2 will allow erosion estimates to be a factor considered as part of forage/grazing planning. Details of how forage harvest operations are implemented will be discussed in a separate report.