Inferring stomatal resistance of sparse crops from infrared measurements of foliage temperature

• Published in: Agricultural and forest meteorology Vol. 42; no. 2; pp. 183 - 198
• Main Authors: Smith, R.C.G., Barrs, H.D., Fischer, R.A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.1988; Oxford Elsevier; New York, NY
• Subjects: Agricultural and forest climatology and meteorology. Irrigation. Drainage; Agricultural and forest meteorology; Agronomy. Soil science and plant productions; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Generalities, techniques; Generalities. Techniques. Climatology. Meteorology. Climatic models of plant production; Water balance and requirements. Evapotranspiration; Monocotyledones; New South Wales; Gramineae; Angiospermae; Spermatophyta; Australia; Cereal crop; Triticum aestivum; Oceania
• ISSN: 0168-1923; 1873-2240
• DOI: 10.1016/0168-1923(88)90076-7

A coupled two-layer model of energy partitioning between soil and foliage for application to sparse crops was used to calculate the mean stomatal resistance from infrared measurements of foliage temperature. The model was tested against diurnal measurements of stomatal resistance, made with a diffusion porometer on two contrasting plots of wheat. One plot was kept well watered (W) and the other plot was left unwatered (D) for 40 days. Soil water deficit conditions had developed on the D plot by the time of measurement. To further test the model, a sensitivity analysis of the calculated stomatal resistance for a wide range of hypothetical leaf areas, foliage temperatures and sensible heat fluxes from the soil was conducted. At 0800 hours the foliage temperature of the W plot was 0.2°C cooler than the D plot. When measurements ceased at 1600 hours the W plot was 3.7°C cooler. As a result of these temperature differences the calculated mean leaf stomatal resistance deviated little from 90 s m −1 on the W plot but increased during the day from 130 to 250 s m −1 on the D plot. These calculated values accounted for 76% of the variance measured by porometer and were close to the 1:1 relationship. The sensitivity analysis indicated the importance of using a coupled two-layer model when calculating stomatal resistance from sparse, water stressed crops. Without such a model the effects of leaf area index on bulk boundary layer resistance and sensible heat flux from soil are ignored and the calculated stomatal resistance is overestimated. This results because drying of the soil can elevate soil surface temperature causing an increase in foliage temperature without any stomatal change.