关键词: 玉米农田, 潜热通量, 显热通量, 日变化, 年变化

Abstract:

Aims Agroecosystems are influenced strongly by human activity and climate change. In order to scientifically manage agroecosystems under climate change, it is important to understand water exchange and energy transfer between agroecosystems and the atmosphere. We analyze latent and sensible heat fluxes of a maize agroecosystem as a case study.

Methods Latent and sensible heat fluxes were measured in a maize agroecosystem using a 3.5 m eddy covariance tower from June 2004 to December 2005 at the Jinzhou maize agricultural ecosystem field observation station (Liaoning Province, China). Meteorological factors were recorded using sensors at 2.3 and 4.1 m using a micrometeorological tower.

Important findings Diurnal and annual variations of latent heat fluxes and sensible heat fluxes had the same characteristics as net radiation and could be expressed as hyperbola curves. Their peak values appeared at 12∶00-13∶00. The maximum latent heat flux was about 655 w·m^-2 (at 13∶00 July 8,2004), and the maximum sensible heat flux was 369 w·m^-2 (at 13∶00 May 31,2004). The intensities of latent heat fluxes and sensible heat fluxes had close relationships with environmental factors. Latent heat flux was negatively correlated with atmospheric pressure, and sensible heat flux was positively correlated with air temperature. Fluxes of latent and sensible heat were very sensitive to precipitation. Latent heat flux was greatly affected by the intensity and timing of precipitation, regardless of seasonal and daily changes. Energy of the maize agroecosystem was unbalanced with the loss of about 15.5%, possibly because of lack of knowledge of 0-5 cm soil heat reserve and canopy heat reserve. The energy balance had obvious differences between cloudy and rainy days, with the loss of energy much less on rainy than cloudy days, especially with a surplus of energy on rainy days in August.

Key words: maize farmland, latent flux, sensible heat flux, diurnal variation, annual variation