Measurement of energy budget components during the International Rice Experiment (IREX) in Japan
✍ Scribed by Y. Harazono; J. Kim; A. Miyata; T. Choi; J.-I. Yun; J.-W. Kim
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 194 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0885-6087
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✦ Synopsis
A ®eld study was conducted to measure the ¯uxes of energy budget components above a rice canopy in Okayama, Japan, from 5 to 16 August 1996. During this period, the canopy height was, on average, 0 . 72 m and the leaf area index was about 3 . 1. The study site was approximately 300 m  300 m, and was surrounded by similar rice ®elds. Our footprint analysis indicated that 490% of the measured ¯ux (at a height of 2 . 2 m above the ground) was expected from within the nearest 300 m of upwind area. The closure of the energy budget was examined to ensure the data quality. Owing to poor thermal conductivity of the heat transducers, soil heat ¯uxes were corrected for the dierence in the thermal conductivities of the paddy soil and the transducer. Eddy covariance ¯uxes were corrected for the eects of line averaging and the sensor separation. Latent heat ¯ux was further corrected for the density ¯uctuations. The magnitudes of the total corrections were not small and amounted to up to 20% of the raw ¯ux values. With these corrections the surface energy budget of a rice stand was closed within 1% under drained conditions and 5% under ¯ooded conditions. The daily evapotranspiration (ET) rate was near the potential rate of open water evaporation and ranged from 4 . 2 to 5 . 8 mm d À1 . In terms of changes in crop water use with irrigation, no dierence in ET rates was found between the drained and ¯ooded conditions.