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Low and variable atmospheric coupling in irrigated Almond (Prunus dulcis) canopies indicates a limited influence of stomata on orchard evapotranspiration.
- Source :
-
Agricultural Water Management . Jan2018, Vol. 196, p57-65. 9p. - Publication Year :
- 2018
-
Abstract
- The degree of coupling to the environment of almond ( Prunus dulcis ) orchards during periods of transient water stress was investigated in a two-year study in California. Plant water status was monitored weekly, before and/or after irrigation, measuring midday stem water potential (Ψ stem ) that ranged from −0.5 to −2 MPa, while actual evapotranspiration (ET a ) was measured with an eddy covariance tower. Irrigation was applied weekly following common commercial practice, resulting in weekly cycles of Ψ stem . Despite Ψ stem reaching levels shown to induce substantial stomatal closure, the ratio actual to reference evapotranspiration (ET a /ET o = K a ) did not show a decrease during weekly periods of low Ψ stem in the two years of the study. Midday average canopy surface resistance (r cmid ), computed by reversing the Penman-Monteith equation from eddy covariance ET data, yielded a statistically significant increase with a decrease in Ψ stem , but just in the first year of the study. However, r cmid did not show a significant relationship with stomatal resistance measured at the leaf level with porometry and scaled-up to the canopy level. In the first year, r cmid showed a sharp increase after harvest, when K a also decreased, perhaps produced by the composite effect of defoliation associated with harvest and stomatal closure associated with water stress. During the growing season, r cmid ranged from 0 to 100 s m −1 and midday average aerodynamic resistance (r amid ) ranged between 0 and 50 s m −1 . Despite r cmid being generally larger than r a , the midday average decoupling factor (Ω) averaged 0.7 during the irrigation season, indicating decoupled conditions. However, there was a large day to day fluctuation of midday Ω ranging from 0.16 to 0.98 mostly associated with r cmid and wind speed. This study indicated that tall and rough canopies can be relatively decoupled depending on the effect of wind speed and canopy resistance on the decoupling factor. From a water management point of view, this result suggests that inducing transient mild to moderate water stress may not produce substantial water savings in areas having low to moderate winds. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 03783774
- Volume :
- 196
- Database :
- Academic Search Index
- Journal :
- Agricultural Water Management
- Publication Type :
- Academic Journal
- Accession number :
- 126363795
- Full Text :
- https://doi.org/10.1016/j.agwat.2017.10.019