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Latent heat fluxes of a soybean field measured and modeled by energy balance-combination models
Abstract
A two-source model based on the energy balance equation and the Penman-Monteith combination equation was used to describe energy exchanges of a soybean canopy and the soil surface. Combination equations which eliminated soil surface resistance to soil latent heat flux were developed, but the equations contained a new variable, the soil surface vapor pressure deficit. Objectives were to quantify soil surface vapor pressure deficit and determine if the modified model improved estimates of soil and total latent heat flux compared with the original model. Research was conducted in 1994 at North Platte, Nebraska. Total latent heat flux from an irrigated soybean field was estimated with the Bowen ratio-energy balance method. Latent heat flux from the soil was measured with microlysimetry. Soil surface vapor pressure deficit was quantified with a device which sampled air near the soil surface. Soil surface vapor pressure was generally underestimated. Drier air from above the soil surface was mixed with near-surface air and reduced its humidity. Soil surface vapor pressure deficit was also underestimated, with the most likely error the underestimation of soil surface temperature. There were no significant differences between the original soil surface resistance model and the modified soil deficit model in the estimation of total or soil latent heat fluxes. Two-source models estimated total latent heat flux much better than a single-source model when the canopy was sparse, but there was no difference when the canopy was full. The models predicted soil latent heat flux best when there was no canopy. Their accuracy decreased when the canopy was sparse and was poorest when the canopy was full. Overestimation of soil latent heat flux by the surface deficit model was attributed to underestimation of soil surface temperature. However, overestimation when the canopy was full was attributed to canopy-dependent factors such as available energy at the soil surface, within-canopy aerodynamic resistance or canopy surface resistance.
Subject Area
Agronomy|Soil sciences
Recommended Citation
Todd, Richard William, "Latent heat fluxes of a soybean field measured and modeled by energy balance-combination models" (1996). ETD collection for University of Nebraska-Lincoln. AAI9712530.
https://digitalcommons.unl.edu/dissertations/AAI9712530