Effect of Canopy Leaf Distribution on Sand Transport and Abrasion Energy

Abstract

During times when crop canopies are short or sparse, wind erosion can damage plants by abrasion and desiccation. Erosion also may uncover plant roots as well as deplete the soil resource. Several studies have reported sand transport among standing stalks, but few 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. These included two canopies with four leaves per plant with the top leaf at either 170 or 130 mm above the surface and oriented in rows normal to the wind direction. The leaf height distribution was changed by moving the leaves so both canopies had a constant leaf area index (LAI) of 0.19. Similarly two canopies were created using two leaves per plant with the pair of leaves at heights of 170 or 70 mm above the surface with a constant LAI of 0.095. The final two canopies were created by doubling the row spacing to give LAI of 0.047. The leaf heights were selected to position the lowest leaves to be either intercepting saltating sand or largely above the saltation layer. The simulated plant canopies were tested in a 15 L x 1.5 H x 1.2 W m push-type recirculating wind tunnel. The tunnel floor was covered with a layer of sieved sand 0.29-0.42 mm in diameter and 25 mm deep. Pitot-static tubes were used to measure wind speeds above and within the canopies. The maximum freestream wind speeds used in the tests ranged from 13 to 17 m s-1. Vertical slot samplers measured sand discharge during 3-minute duration test runs. Relative abrasion energy was determined by mass of soil loss abraded from both flat and vertical containers placed in the canopy. The target soil for abrasion was created using a mixture of silty and fine, sandy soils that was puddled and then dried to create a uniform, weakly-consolidated test medium.