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ARS Home » Plains Area » El Reno, Oklahoma » Grazinglands Research Laboratory » Agroclimate and Natural Resources Research » Research » Publications at this Location » Publication #332266

Research Project: AGRICULTURAL LAND MANAGEMENT TO OPTIMIZE PRODUCTIVITY AND NATURAL RESOURCE CONSERVATION AT FARM AND WATERSHED SCALES

Location: Agroclimate and Natural Resources Research

Title: Residue decomposition of submodel of WEPS

Author
item Van Donk, Simon - University Of Nebraska
item Steiner, Jean
item Schomberg, Harry
item Unger, Paul
item Fox, Jr, Fred

Submitted to: USDA Miscellaneous Publication 1343
Publication Type: Book / Chapter
Publication Acceptance Date: 1/17/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: The Residue Decomposition model of the Wind Erosion Prediction System (WEPS) simulates the decrease in crop residue (biomass) due to microbial activity. The decomposition process is modeled as a function of temperature and moisture in terms of decomposition days; under optimum temperature and moisture conditions one decomposition day per day is accumulated while only a fraction of a decomposition day is accumulated if less than optimum conditions occur. Biomass remaining after harvest is partitioned between various pools representing standing, flat, buried, and root biomass. Residue from different crops may decompose at different rates. Since residue decomposition can require a long period of time, crop residue biomass from sequential harvests is accounted for in three separate pools. Biomass from the most recently harvested crop will be in pool one, biomass from the previous crop in pool two, and there is a third pool for biomass from the oldest crop(s). After harvest, any residue biomass remaining from a previous crop is moved into the older age pools and residue from the just harvested crop is moved into pool one. Standing residue losses not only result from microbial activity, but also from physical forces. A daily estimate of the standing stem population is required in order to evaluate the vertical stem area that the wind encounters and thus wind resistance and, ultimately, wind erosion. Tillage may alter the amount of residue in the different pools. The Residue Decomposition model of WEPS is the only model that simulates the residue decomposition as it affects erodibility for improved simulation of wind erosion.

Technical Abstract: The Residue Decomposition submodel of the Wind Erosion Prediction System (WEPS) simulates the decrease in crop residue biomass due to microbial activity. The decomposition process is modeled as a first-order reaction with temperature and moisture as driving variables. Decomposition is a function of decomposition days; under optimum temperature and moisture conditions, one decomposition day per day is accumulated, but only a fraction of a decomposition day is accumulated if less than optimum conditions occur. Biomass remaining after harvest is partitioned between standing, flat, and buried position pools. Residue from different crops may have different properties and decompose at different rates. Therefore, each event that creates residue places it into one of five unique age pools. After harvest, any residue biomass remaining from a previous crop is moved down one age pool and residue from the just harvested crop is moved into the first age pool. The fifth age pool accumulates remaining biomass from the oldest crop(s). Standing residue losses not only result from microbial activity, but also from physical forces. Transfer of crop residue from the standing biomass position pool will reduce stem population and standing biomass. A daily estimate of the standing stem population is required to evaluate the vertical stem area that the wind encounters. This area is quantified by the stem area index, which is calculated from standing stem number, stem height, and stem diameter. It affects aerodynamic resistance and, ultimately, wind erosion. Stems start to fall after reaching a threshold of cumulative decomposition days after harvest. Both standing and flat crop residue provide cover to the soil surface, protecting it against wind erosion. Soil cover from flat residue is calculated from flat residue mass. Tillage may alter the amount of residue in the different position pools. The WEPS Residue Decomposition model was compared and contrasted with other residue decomposition models and five simulation scenarios were created to illustrate its functionality. The Residue Decomposition submodel of WEPS is the only model that simulates the residue decomposition as it affects erodibility for improved simulation of wind erosion.