Effects of irrigation on near surface energy budget distribution as influenced by soybean canopy

Effects of irrigation on near surface energy budget distribution as influenced by soybean canopy

1999

A:PS

The effects of crop canopy on net radiation, sensible heat, and evaporative latent heat flux mechanisms based on the energy budget balance assumption at the near surface atmospheric boundary layer were discussed. This paper compares the diurnal variation before and after irrigation by measuring microclimatic change. The study was carried out in Hsuehchia Upland Crop Irrigation Experimental Station on May 1994. Climatic data including wind velocity, air temperature, net radiation, and soil surface temperature, soil surface heat flux, and other correlated edaphic data were collected simultaneously. The crop factors included leaf area index and distribution of leaves within vertical profile. Canopy architecture and physiology were the major factors affecting energy transfer in canopy stands. Meanwhile, there was significant interaction among the incident solar radiation angle, the optical properties of leaf area, and the tillage direction in field. The momentum transfer was forced not only by the friction but also by the form drag when air flow. The penetration function, which equals the ratio of soil net radiation and global net radiation, was estimated by Beer-Bougher exponential declining law. The sensible heat transfer was derived by Monin-Obukhov similarity theorem. And exponential wind vertical distribution assumption, leaf area index, and turbulent diffusivity at the top of canopy were used to derive the aerodynamic resistance of sensible heat. The evaporative latent heat was be obtained by energy balance method. Results showed that the sensible heat transfer at both canopy layer (Hc(+)) and soil boundary layer (Hs(-)) were more intense before irrigation than aider it. And before irrigation, the amount of the evaporative latent heat flux of the soil boundary layer can reach 90 percents of the amount of the gross one in atmosphere according energy budget balance theory. The role of evaporative latent heat flux in canopy layer before irrigated was vice versa. It demonstrated that the canopy has significant function in regulating the energy budget balance near ground.

1999:223-233, AGRICULTURAL ENGINEERING RESEARCH CENTER RESEARCH BULLETIN

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