Effect of canopy leaf distribution on sand transport and abrasion energy

Abstract

Abstract During times when crop canopies are short or sparse, wind erosion can uncover plant roots, deplete the soil resource, and damage plants by abrasion and desiccation. Few studies have considered the effects of position and number of leaves on sand transport and the distribution of the sand abrasion energy. The objectives of this study were to determine the effects of number and distribution of leaves on threshold velocities, sand transport rates, and relative abrasion energy among simulated dicotyledonous plant canopies. Six canopies were tested in a wind tunnel with two levels of leaf area index (LAI), two different maximum leaf heights, and either two or four leaves per plant with maximum freestream wind speeds from 12 to 17 m s −1 . The leaf heights were selected to position the lowest leaves to be either intercepting saltating sand or largely above the saltation layer. The wind tunnel was a 1.52 W × 1.82 H × 15.3 L m push-type recirculating tunnel with the floor covered with a layer of sieved sand. Sand discharge and relative abrasion energy were measured during 3-min duration test runs. For canopies with two leaves, the experimental sand transport capacity was reduced most when the leaves were highest above the surface even though they were intercepting saltation when in their lowest positions. As expected, canopy LAI was directly related to threshold velocity and inversely related to sand transport capacity. Total abrasion energy impacting the target soil channel containers located vertically in the canopy increased with wind speeds above the threshold. Within canopies, high wind speeds increased height of maximum abrasion but often still caused less total abrasion per unit sand discharge than over a bare, sandy surface. When leaves were located nearest the surface, they modified the vertical abrasion profiles by deflecting a portion of the sand impact energy upward in the wind stream. Overall, the canopies modified both the profiles and normalized abrasion energy of the sand discharge when compared with a bare, sandy surface. Hence, it may be important to place test plants within a canopy of similar plants—to allow development of a fully developed velocity profile in the canopy by using a minimum upwind fetch of about 70 canopy heights in a wind tunnel—when conducting plant abrasion tests using sand to achieve results representative of plants in the interior of a field. In contrast, abrasion on inter-row flat soil containers was independent of wind speeds, but was higher without a canopy compared with measurements in the canopy for a given sand discharge.