Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 11, 2003
Publication Date: July 1, 2003
Citation: Aiken, R.M., Nielsen, D.C., Ahuja, L.R. 2003. Scaling effects of standing crop residues on the wind profile. Agronomy Journal 95:1041-1046. Interpretive Summary: Standing crop residues protect the soil from erosive winds that can deplete soil water. Knowledge of the insulating effects of various crop residues can guide land management decisions. We adapted and evaluated theory derived for growing crops to standing dead crop residues. After adjusting theoretical values for shape of standing residues, the adapted theory accounted for 98% of the variation observed in wind speeds near the land surface. These equations can be readily applied to existing crop management models, which guide soil and water conservation.
Technical Abstract: Standing, but senescent stems increase the aerodynamic roughness of the boundary layer, reducing wind energy available for momentum transfer at the soil surface, and reducing the soil-atmosphere convective exchange of heat, water vapor and trace gases. We conducted studies to determine the predictive accuracy of algorithms, derived for plant canopies, which scale effects of standing crop residues on the wind profile. We calculated aerodynamic properties of standing crop residues, related to the log wind profile equation, by substituting stem area index for leaf area index in these algorithms. We calculated apparent roughness length for wind profiles measured, under neutral stability conditions, over wheat (Triticum aestivum), corn (Zea mays), millet (Panicum miliaceum) and sunflower (Helianthus annuus) stems using calibrated single needle and cup anemometers at up to ten heights ranging from 0.07m to 2.40m above the soil lsurface on fields with fetch: height ratios exceeding 200:1. A least- squares fit of roughness length, calculated by an algorithm derived for crop canopies, indicated a systematic, positive bias when applied to standing stems. Predictive error (RMSE) within profiles ranged from 0.5 to 4.6% of reference wind speed; the coefficient of determination exceeded 0.98 in all cases. The non-linear forms of the scaling algorithms are consistent with theory and wind tunnel observations. This advance warrants evaluation of the adjusted algorithm for simulation of energy balance, microclimate, and pest population dynamics in the soil-residue-crop canopy regime. Application to momentum transfer problems requires further investigation of drag partitoning.