Wednesday, 8 October 2008: 2:00 PM

George R. Brown Convention Center, 362DE

Matthias Langensiepen, Modelling Plant Systems, Humboldt-University of Berlin, Invalidenstrasse 42, Berlin, 10115, Germany, Marcel Fuchs, Environmental Physics and Irrigation, Agricultural Research Organization, Institute of Soil, Water and Environmental Sciences, Volcani Center POB 6, Bet Dagan, 50250, Israel, Homero Bergamaschi, Faculdade de Agronomia, Departamento de Plantas Forrageiras e Agrometeorologia, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 7712, Agronomia 91501-970, Porto Alegre, 15100, Brazil, Samuel Moreshet, Department of Environmental Physics and Irrigation. Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization of the Israel Ministy of Agriculture, POB 6, Bet-Dagan, 50250, Israel, Yehezkel Cohen, Agricultural Research O, Agricultural Research Organisation of the Israel Ministry of Agriculture, 2Department of Environmental Physics and Irrigation, Institute of Soil, Water and Environmental Sciences, POB 6, Bet.Dagan, 50250, Israel, Shabtai Cohen, 2Department of Environmental Physics and Irrigation, Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization of the Israel Ministry of Agriculture, POB 6, Bet-Dagan, 50250, Israel, Peter Wolff, University of Kassel, Heiligenstädter Weg 5, Witzenhausen, 37213, Germany, Samuel C. Jutzi, Animal Production and Health Division, FAO Headquarters, delle Terme di Caracalla, Rome, 00100, Italy, Louis M. G. Rosa, Departamento de Plantas Forrageiras e Agrometeorologia, Universidade Federal do Rio Grande do Sul, Faculdade de Agronomia, Bento Gonçalves 7712, Agronomia 91501-970, Porto Alegre, Brazil and Yan Li, CAS, 40-3 South Beijing Road, Xinjiang Institute of Ecology and Geography, Xinjiang, 830011, China

The Penman-Monteith equation was used for calculating the actual transpiration of optimum-managed maize crops under the contrasting climate conditions of

Brazil

Germany

and

Israel

. In-situ measurements of light interceptance and stomatal conductance were correlated and the resulting light response function was scaled to the canopy level using a light penetration model. The transpiration model was tested against 10634 independent sap flow measurements in maize stems. Measured and calculated 15-minute or 30-minute averaged transpiration rates are highly correlated (r²=0.95) and the slope of the regression line is close to unity (y=0.989x+0.002). The overall root mean square error (RMSE) of calculated transpiration minus measured sap flow is 0.08 mm/hr and dominated by its variance component (0.005 {mm/hr}²). Measured sap flow consistently lagged behind calculated transpiration, because plant hydraulic capacitance delayed the change of leaf water potential that drives water uptake. Calculated transpiration significantly overestimated sap flow during morning hours (mean = 0.068 mm/hr) and underestimated it during afternoon hours (mean = -0.065 mm/hr).

Calculated daily transpiration closely followed the measured trends at the three locations during two successive years. The RMSE of daily calculated transpiration minus measured sap flow was 0.6 mm / day. It was dominated by its variance component (variance=0.3 {mm/day}²; bias=0.2 mm/day). No significant differences were found between seasons and locations. Statistical uncertainties of canopy conductance parameterizations led to computation errors of up to 2.1 mm/day. The model responded most sensitively to a 30 percent change of net radiation (Absolute bias error =1.6 mm/day), followed by corresponding alterations of canopy resistances (0.8 mm/day), vapour pressure deficits (0.5 mm/day) and aerodynamic resistances (0.34 mm/day). The Penman-Monteith approach as implemented in the present study is sufficiently sensitive to detect small differences between transpiration and water uptake and provides a robust tool for managing plant water supply under unstressed conditions.

See more of: Sixty Years of the Penman Equation to Calculate ET/Div. A03 Business Meeting
See more of: A03 Agroclimatology & Agronomic Modeling

2008 Joint Annual Meeting (5-9 Oct. 2008): Application of the Penman-Monteith Equation under Contrasting Climate Conditions.

703-4 Application of the Penman-Monteith Equation under Contrasting Climate Conditions.