Fine root distributions and water consumption of alfalfa grown in layered soils with different layer thicknesses

Abstract

Although creation of layers with different textures in topsoil is known to increase available water holding capacity (AWHC) and plant survival, little is known about associations between the layers and fine root density (FRD) or water consumption. This study investigates the effects of alternating a coarse sand layer over a finer loess layer on alfalfa growth. Soils were packed into 90-cm long columns, either individually or in alternating layers. The three layered soils had layer thicknesses of 11.25, 22.5 or 45cm. Soils were saturated, allowed to drain freely and the AWHC was determined. Alfalfa, sown in the columns, grew for 15 days before an irrigation regime was applied to all columns. The net photosynthetic rate (PN) and profile soil water content were measured during the three-month growing period. Shoot, root, and total dry biomass and FRD were measured after the experiment ended. The AWHC was considerably increased by decreasing the layer thickness. The FRD decreased with depth, and was greater in the loess than in the sand. Decreasing layer thickness increased FRD in the loess layers. Root and shoot growth, water consumption, transpiration and alfalfa biomass all increased in the layered soils relative to the homogeneous soils. Hence, alfalfa biomass increased in response to decreasing layer thickness. These results can be used to test and validate mining soil reclamation and/or arid agricultural water management practices in the field.