Overestimation of soybean crop transpiration by sap flow measurements under field conditions in Central Portugal
✍ Scribed by Gerrit Gerdes; Bruce E. Allison; Luis S. Pereira
- Publisher
- Springer
- Year
- 1994
- Tongue
- English
- Weight
- 507 KB
- Volume
- 14
- Category
- Article
- ISSN
- 0342-7188
No coin nor oath required. For personal study only.
✦ Synopsis
Direct measurements of the xylem sap flow by the stem heat balance technique can be a valuable aid for determining the irrigation demand of field crops. In the present study, soybean (Glyr max (L.) Merr.) sap flow was evaluated under well-watered and water-stressed conditions using Dynamax SGA10 sap flow gauges. Solar radiation was measured continuously throughout the growing season. Soil water content was measured before and after each irrigation. There was a close relationship between solar radiation and xylem sap flow. The water flux in the soybean stems responded realistically to changes in the soil water content. However, the absolute values of sap flow were highly questionable. Calculating crop transpiration from sap flow measurements, the resuits were up to 4 times as high as calculated transpiration from soil moisture data and simulated transpiration using the locally calibrated soybean crop growth model SOYGRO. A sensitivity analysis of the stem heat balance technique gave no indications of technique or input errors. The gauge design was possibly not appropriate for the outdoor installation on soybeans.
The water flux in the stem of intact plants can be measured directly using the stem heat balance (SHB) technique according to Sakuratani (1981). Since the xylem sap flow is closely related to transpirational water losses (about 99% of plant water uptake is lost by transpiration), sap flow is assumed to equal transpiration. The relative accuracy of the SHB method compared with direct weighing of water losses is reported to be about +10% (Sakuratani 1981(Sakuratani , 1984(Sakuratani , 1987;;Baker and Van Bavel 1987;Steinberg et al. 1990). However, most of the studies using the SHB technique were conducted in controlled environments. The objective of this study was to determine soybean crop transpiration by sap flow measurements under well-watered and water-stressed condi-