Estimation of the leaf stomatal conductance in pumpkin under different nitrogen levels using leaf temperature

Since stomatal conductance (gs) couples the crop photosynthesis and transpiration, estimation of gs is important for adopting management practices which can increase crop growth through efficient use of water. In the current study, a simple model based on temperature difference between crop leaf and a reference surface was used for estimation of the leaf stomatal conductance. The model calibrated and validated using two years field experiment data with pumpkin carried out during 2013 and 2014 at Research Farm of Ferdowsi University of Mashhad. Results showed that model had a very good performance and very accurately simulated pumpkin leaf stomatal conductance under conditions without nitrogen deficiency. Under nitrogen deficient conditions, by using the nitrogen nutrition index (NNI), the good or very good performance and accuracy were obtained from the model. The relative difference (RD) between simulated and observed values of average of stomatal conductance during the growing season was ranged from 1.1% to 2.5 for non-nitrogen deficient treatments and from 2.8% to 5% for nitrogen deficient treatments. The accuracy and simplicity of the model and its low input requirements make it suitable for use in stomatal conductance based crop growth models.