Discrimination of water stress in pepper using thermography and leaf turgor pressure probe techniques

The use of technology is spreading rapidly in modern agriculture with remote sensing and sensor technologies becoming more important. The objective of this study is to investigate the possibilities of determining the water stress level and irrigation time in peppers using leaf pressure probes based on turgor pressure and thermography techniques. An experiment consisting of four different irrigation treatments (100%, 75%, 50% and 25%) was conducted in Canakkale province, Turkey in the 2017-2018 summer growing seasons. During this seasons, leaf turgor pressure (Pp) and soil moisture levels were recorded in real time by a remote monitoring system. Thermographic measurements were taken before each irrigation. Data were analyzed using the analysis of variance and regression tree methods. Results show that both Pp and thermal data significantly differed according to water stress. Pp values decreased partially after irrigation and increased until the next irrigation. However, it was observed that it is not enough to decide the irrigation time using results obtained from graphical readings only. Models including meteorological features strengthen the decision-making models. According to the classification and regression tree analysis, it was revealed that there is a potential to separate the treatments, especially in models including thermal indices. Leaf turgor pressure data and thermal indices, which are plant-based monitoring techniques, have the potential to be used in determining irrigation time and distinguishing water stress in the pepper plant. However, there is a need for more studies especially in laboratory conditions, to understand the mechanisms in plants and how environmental conditions affect the responses of Pp probes.