Short-term effects of land leveling on soil physical properties and microbial biomass

Land leveling is a practice that facilitates more uniform delivery of irrigation water. However, the spatial variability and distributions of soil physical and biological properties, and the relationships between them, are not well characterized in agroecosystems that have been land leveled. The objectives of this study were to characterize the short-term impacts of land leveling on the magnitudes, spatial variability, and spatial distributions of soil physical and biological properties, and to evaluate the relationships between these properties in a Stuttgart silt loam (fine, smectitic, thermic Albaqultic Hapludalf) used for irrigated soybean [Glycine max (L.) Merr.] and rice (Oryza sativa L.) production in eastern Arkansas. Bulk density and sand and clay contents significantly increased, while silt content and fungal and bacterial biomass significantly decreased, as a result of land leveling. Land leveling did not change the fungal/bacterial biomass ratio indicating that, despite the effect leveling had on the relative abundance of the fungal and bacterial biomass, the relative proportion of fungal/bacterial biomass, hence the structure of the soil microbial community, remained unaffected as indicated by soil-sample staining methods. Land leveling significantly changed the variance associated with soil biological properties, but the variances of soil physical properties were unaffected. The relationships between soil physical and biological properties also changed significantly as a result of land leveling, but the ability to predict soil biological properties from soil physical properties was surprisingly poor. These results indicate that variability in soil biological properties may play an important role in restoring productivity to precision-leveled soils.