This study was conducted to determine crop water stress index (CWSI) values and irrigation timing in the case of Derinkuyu dry bean ( Phaseolus vulgaris L.). In 2017, dry beans were grown as the main crop according to the field design consisting of plots divided into randomised blocks. Irrigation treatment comprised full irrigation (I100) and irrigation issues with three different levels of water stress (I66, I33, I0). This study applied 602 mm of water under the I100 irrigation. The yield of Derinkuyu dry beans was equal to 3576.6 kg∙ha ^–1 in I100 irrigation. The lower limit (LL) value, which is not necessary for the determination of CWSI, was obtained as the canopy–air temperature difference ( Tc – Ta) versus the air vapour pressure deficit ( VPD). The upper limit (UL) value, at which the dry beans were wholly exposed to water stress, was obtained at a constant temperature. The threshold CWSI value at which the grain yield of dry beans started to decrease was determined as 0.33 from the measurements made with an infrared thermometer before irrigation in I66 irrigation treatment. As a result, it can be suggested that irrigation should be applied when the CWSI value is 0.33 in dry beans. Furthermore, the correlation analysis revealed a negative correlation between grain yield and crop water stress index and a positive correlation between yield and chlorophyll content. According to variance analysis, significant relationships were found between the analysed parameters at p ≤ 0.01 and p ≤ 0.05.

According to the SRES A1B climate change scenario, by the end of the 21st century temperature in Poland will increase by 2–4°C, no increase in precipitation totals is predicted. This will rise crop irrigation needs and necessity to develop irrigation systems. Due to increase in temperature and needs of sustainable agriculture development some changes in crop growing structure will occur. An increase interest in high protein crops cultivation has been noted last years and further extension of these acreage is foreseen. Identifying the future water needs of these plants is crucial for planning and implementing sustainable agricultural production. In the study, the impact of projected air temperature changes on soybean water needs, one of the most valuable high-protein crops, in 2021–2050 in the Kuyavia region in Poland was analysed. The calculations based on meteorological data collected in 1981–2010 were considered as the reference period. Potential evapotranspiration was adopted as a measure of crop water requirements. The potential evapotranspiration was estimated using the Penman–Monteith method and crop coefficient. Based on these estimations, it was found that in the forecast years the soybean water needs will increase by 5% in the growing period (from 21 April to 10 September), and by 8% in June–August. The highest monthly soybean water needs increase (by 15%) may occur in August. The predicted climate changes and the increase in the arable crops water requirements, may contribute to an increase in the irrigated area in the Kuyavia region and necessity of rational management of water resources.