Effects of Water Stress on Spectral Reflectance of Potato Crop Grown in Open Field Conditions

Potato belongs to the Solanaceae family, which is known for being highly susceptible to abiotic stress, particularly related to water. Understanding how and to what extent potato plants respond to different wavelengths of light is essential for gaining insights into soil water and plant water status, chlorophyll levels, and optimal timing for watering. Studying the spectral response of potato plants before and after irrigation, particularly focusing on agricultural management, resource optimization, and enhancing crop output. This study aimed to investigate the spectral characteristics of potato plants before and after irrigation, while plants are under varying soil-water conditions. This was achieved by implementing different irrigation schedules that maintained soil moisture levels at 25%, 50%, 65%, and 85% of the Maximum Allowable Depletion (MAD) of Available Soil Moisture (ASW). The plants' spectral responses were measured using a portable spectroradiometer. During the vegetative stage of the potato crop, plants treated with MAD50 and MAD25 experienced a slightly higher spectral reflectance in the green band spectrum before irrigation indicating healthy plants (Chlorophyll abundance). In general, MAD50-treated plants showed a higher spectral reflectance than plants treated with MAD25, MAD65, and MAD85 in the red-edge band (730-750nm) and NIR band spectrum. Furthermore, MAD85-treated plants exhibited higher spectral reflectance in all spectra than MAD65, MAD50, and MAD25-treated plants after irrigation. However, the red band (around 680nm) was almost saturated for all plants treated with MADs before and after irrigation, except MAD85-treated plants, after irrigation.  In addition, we have found the least variations in spectral reflectance of the MAD25 and MAD50-treated plants prior and post-irrigation. Whereas, MAD65 shows a spectral reflectance increase of +1.54-2.97% in the green band and +2.23-12.18% in the red-edge and NIR band after irrigation. Similarly, MAD85 exhibits a reflectance increase of +3.56-6.29% in the green band and +4.24-19.73% in the red-edge and NIR band after irrigation.  These findings highlight that optimum soil moisture is required for plants to be effective in MAD25 and MAD50 compared to the other delayed irrigation conditions. This research suggests an effective irrigation schedule to adapt in situations where adverse impacts of climate change, such as unpredictable water supply, water scarcity, and decreased irrigation expenses affects production. Assessing the baseline spectral response of crops before irrigation aids in detecting indications of water stress, while post-irrigation assessment helps determine whether the provided water has relieved stress and promoted robust plant development.

Keywords: Potato crop, Spectral response, Handheld Spectroradiometer, Water-stress, Irrigation