Observations were made of stomatal behaviour of groundnut growing in glasshouses. Stomatal resistance or its reciprocal, conductance, varies throughout a canopy: between different parts of a leaf, between upper and lower surfaces, between leaves and between plants. The response of stomatal behaviour to environmental factors was analysed. Fig. 4 shows an example of responses of conductance to environmental factors such as air temperature, irradiance and vapour pressure deficit. It is also seen that leaf conductance increases with soil moisture. Under full cover of plants and with wet soil, the following relation between canopy conductance and environmental variables has been found:
gc = 0.299 (IR/VPD) - 0.089, (r = 0.94)
where gc—canopy conductance (cm/s), IR—intercepted radiation (W/m2), VPD—vapour pressure deficit (mba), r—correlation coefficient.