Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2016
Publication Date: 10/13/2016
Citation: Zaibon, S., Anderson, S.H., Kitchen, N.R., Haruna, S.I. 2016. Hydraulic properties affected by topsoil thickness in switchgrass and corn-soybean cropping systems. Soil Science Society of America Journal. 80(5):1365–1376. doi: 10.2136/sssaj2016.04.0111.

Interpretive Summary: Degraded land is defined as land that has lost the capacity to support plant growth as a result of intensive agricultural practices and enhanced soil erosion. The loss of topsoil thickness from erosion on claypan soils reduces productivity due in part to decreased soil water holding capacity, infiltration, and hydraulic conductivity. The objective of this research was to evaluate the effects of claypan soil topsoil thickness and cropping systems (perennial switchgrass bioenergy crop versus corn-soybean grain crop) on important soil hydraulic properties. We found that switchgrass improved soil hydraulic properties in claypan landscapes as compared to a corn-soybean rotation system. Switchgrass had 3% lower bulk density, 73% greater hydraulic conductivity, 11% higher saturated water content, and 53% larger proportion of soil macro pores as compared to the grain crops. In related investigations we concurrently found switchgrass to have greater water use efficiency. Variable topsoil thickness (or degree of erosion) was the main factor controlling these hydraulic properties. Thus, the establishment of switchgrass favors more continuous and more permanent soil pores which contributes to improved soil hydraulic properties. This in turn will result in less runoff from these marginal soil landscapes. This work benefits farmers and the public because it helps them know the benefits of growing a cellulosic bioenergy crop on degraded soils. These benefits help restore soil function, and with restored function the soil is healthier and more sustainable for future food, fiber, and fuel crop management systems.

Technical Abstract: Loss of productive topsoil by soil erosion over time can reduce the productive capacity of soil and can significantly affect soil hydraulic properties. This study evaluated the effects of reduced topsoil thickness and perennial switchgrass (Panicum virgatum L.) versus corn (Zea mays L.)/soybean [Glycine max (L) Merr.] rotation on soil bulk density ('b), saturated hydraulic conductivity (Ksat), soil water retention, and pore size distributions. The experiment was conducted at University of Missouri South Farm on a Mexico silt loam (Vertic Epiaqualfs). Twenty-seven years after establishment, plots with selected topsoil thickness were grouped in four treatments [TopA (4 cm), TopB (11 cm), TopC (22 cm), and TopD (36 cm)]. Plots with corn-soybean rotation and switchgrass were established in 2009 with four replicates. Sample cores, 76 mm by 76 mm, were collected by 10 cm depth increments from the surface to the 40 cm depth. Results showed that switchgrass had 53% and 27% higher macroporosity (>1000 um diam.) and coarse mesoporosity (60 to 1000 um diam.), respectively, compared to row crop management. This led to 73% greater Ksat and 11% higher water content at saturation as compared to row crop management. Thicker topsoil treatments (TopC and TopD) had consistently lower 'b and greater Ksat than the shallow topsoil treatments (TopA and TopB) for all sampling depths. These results imply that switchgrass production systems significantly improve soil hydraulic properties particularly in eroded claypan landscapes.