Surface energy balance partitioning in tilled and non-tilled bare soils

Knowledge of the partitioning of the surface energy balance (SEB) components is essential in understanding heat and water budgets at the soil-plant-atmosphere interface. Agriculturally, changes in soil structure due to soil tillage in the fall and spring affects the magnitude of these components. SEB partitioning determined by modeled and measured studies usually assumes a constant near surface bulk density values for extended periods of time. The objectives of this study is to determine the effect of soil bulk density changes on net radiation, soil heat flux (G), latent heat flux (LE) and sensible heat flux (H) of a tilled and non-tilled bare soil with time. Micro-Bowen ratio (MBR) system were set up for 91 days on a tilled (Till) soil and a non-tilled (NT) soil at the Iowa State University Agronomy and Agricultural Engineering Research farm near Ames. MBR systems measured water vapor and air temperature at 0.01 and 0.06 m heights above the soil surface, to determine atmospheric gradients for LE and H calculations. Net radiation was obtained by a net radiometer positioned at 1.25 m above the surface, while soil heat flux measurements were obtained from soil heat flux plates at a 0.06 m depth and soil heat storage calculations (0- 0.06 m). Evaporation rates were also determined by micro-lysimeters. Two time periods, were selected early and late in the season (relative to tillage), to determine the effect of changing bulk density with time. Bulk density showed little to no change following tillage in Period 1 but increased by 0.11 g cm-3 following substantial rainfall events at the Till plot during Period 2. In Period 1, Rn and G fluxes did not differ between plots as bulk density and water contents were similar. The Till soil LE flux was 12% higher than in the NT according to the MBR measurements and 15% higher according to the ML measurements. In Period 2 (DOY 262-266), Rn and G fluxes showed relatively larger daytime difference between Till and NT. As bulk density and water content increased during this period, G fluxes represented 7% more Rn at the Till soil than in the NT soil. A subsequent 7% lower available energy was observed at the Till plot leading to 10% lower LE values for Period 2. The results of this research highlight the value of considering dynamic bulk density measurements with time when determining the distribution of energy at the soil surface

Surface Energy Balance Partitioning in Tilled Bare Soils

Core Ideas Following tillage, soil bulk density increased after rainfall. Increases in soil bulk density decreased the available energy for turbulent fluxes. Surface energy balances in tilled soils are affected by changes in bulk density. Surface energy balance (SEB) partitioning is critical to heat and water budgets at the soil–atmosphere interface. Tillage can alter SEB partitioning by initially decreasing soil bulk density (ρb), after which ρb increases with time due to rainfall and other factors. The objective of this study is to determine the effect of ρb changes on SEB partitioning. We measured SEB components for two 4‐d periods (Period 1 and Period 2) at an early‐tilled (T1) and late‐tilled (T2) bare soil site. During Period 1, ρb, net radiation, and soil heat flux were similar for T1 and T2, but evaporation was higher at T2. During Period 2, ρb was 0.11 g cm‾3 larger at T2 than at T1. This resulted in a 7% higher soil heat flux at T2, which in turn caused 13% less evaporation. These results highlight the importance of considering dynamic ρb with time when determining SEB partitioning for tilled soils

Surface energy balance partitioning in tilled and non-tilled bare soils

Knowledge of the partitioning of the surface energy balance (SEB) components is essential in understanding heat and water budgets at the soil-plant-atmosphere interface. Agriculturally, changes in soil structure due to soil tillage in the fall and spring affects the magnitude of these components. SEB partitioning determined by modeled and measured studies usually assumes a constant near surface bulk density values for extended periods of time. The objectives of this study is to determine the effect of soil bulk density changes on net radiation, soil heat flux (G), latent heat flux (LE) and sensible heat flux (H) of a tilled and non-tilled bare soil with time. Micro-Bowen ratio (MBR) system were set up for 91 days on a tilled (Till) soil and a non-tilled (NT) soil at the Iowa State University Agronomy and Agricultural Engineering Research farm near Ames. MBR systems measured water vapor and air temperature at 0.01 and 0.06 m heights above the soil surface, to determine atmospheric gradients for LE and H calculations. Net radiation was obtained by a net radiometer positioned at 1.25 m above the surface, while soil heat flux measurements were obtained from soil heat flux plates at a 0.06 m depth and soil heat storage calculations (0- 0.06 m). Evaporation rates were also determined by micro-lysimeters. Two time periods, were selected early and late in the season (relative to tillage), to determine the effect of changing bulk density with time. Bulk density showed little to no change following tillage in Period 1 but increased by 0.11 g cm-3 following substantial rainfall events at the Till plot during Period 2. In Period 1, Rn and G fluxes did not differ between plots as bulk density and water contents were similar. The Till soil LE flux was 12% higher than in the NT according to the MBR measurements and 15% higher according to the ML measurements. In Period 2 (DOY 262-266), Rn and G fluxes showed relatively larger daytime difference between Till and NT. As bulk density and water content increased during this period, G fluxes represented 7% more Rn at the Till soil than in the NT soil. A subsequent 7% lower available energy was observed at the Till plot leading to 10% lower LE values for Period 2. The results of this research highlight the value of considering dynamic bulk density measurements with time when determining the distribution of energy at the soil surface.</p

Surface Energy Balance Partitioning in Tilled Bare Soils

Core Ideas Following tillage, soil bulk density increased after rainfall. Increases in soil bulk density decreased the available energy for turbulent fluxes. Surface energy balances in tilled soils are affected by changes in bulk density. Surface energy balance (SEB) partitioning is critical to heat and water budgets at the soil–atmosphere interface. Tillage can alter SEB partitioning by initially decreasing soil bulk density (ρb), after which ρb increases with time due to rainfall and other factors. The objective of this study is to determine the effect of ρb changes on SEB partitioning. We measured SEB components for two 4‐d periods (Period 1 and Period 2) at an early‐tilled (T1) and late‐tilled (T2) bare soil site. During Period 1, ρb, net radiation, and soil heat flux were similar for T1 and T2, but evaporation was higher at T2. During Period 2, ρb was 0.11 g cm‾3 larger at T2 than at T1. This resulted in a 7% higher soil heat flux at T2, which in turn caused 13% less evaporation. These results highlight the importance of considering dynamic ρb with time when determining SEB partitioning for tilled soils.This article is published as Akuoko, Ohene, Dilia Kool, Thomas J. Sauer, and Robert Horton. "Surface energy balance partitioning in tilled bare soils." Agricultural & Environmental Letters 3, no. 1 (2018): 1-4. doi: 10.2134/ael2018.07.0039.</p