Determination of yield and quality changes in winter squash (Cucurbita maxima Duch.) depend on partial rootzone drying and water stress

This study was conducted to investigate the effects of partial rootzone drying and deficit irrigation treatments on yield, quality traits (soluble solids content, pH, titratable acidity) and physiological parameters (leaf water potential, leaf relative water content, chlorophyl content) of drip-irrigated winter squash (Cucurbita Maxima Duch.) and to determine plant water consumption, water and irrigation water use efficiencies in 2017 and 2019 growing seasons of Tokat province. The effects of 6 different subjects were examined as: full irrigation (FI), deficit irrigations (DI-30, DI-50), fixed and alternate partial rootzone drying (FPRD, APRD) and non-irrigated (rain-fed, RF) treatments. Plant water consumptions varied between 178.7 and 433.8 mm in 2017 and between 230.1 and 472.5 mm in 2019. Marketable yield values varied from 2 220 to 4 036 kg/da in 2017 and from 2 989 to 5 230 kg/da in 2019. Water use efficiency (WUE) values varied between 9.3 and 10.6 kg/m3 in 2017 and between 10.9 and 12.5 kg/m3 in 2019. Irrigation water use efficiency (IWUE) values varied between 14.3 and 21.2 kg/m3 in 2017 and between 14.9 and 25.3 kg/m3 in 2019. Yield response factor (ky) was calculated as 0.82 in 2017 and as 0.76 in 2019, the average was 0.79. In the second year of the study, potential use of crop water stress index (CWSI) in irrigation scheduling was also investigated. The CWSI value varied from 0.22 to 0.97 and it was determined that high yields would be obtained when irrigation was done at CWSI values of between 0.22 to 0.38. There was a strong (R=0.97) relationship between yield and CWSI as Y=-3119.2×CWSI+6118.2. As compared to FI treatment, about 47% water saving was achieved with DI-50, FPRD and APRD treatments with relative yield losses of 17, 23 and 25%, respectively. Based on the present findings it was concluded that partial rootzone drying irrigation technique did not produce a significant advantage in terms of yield and quality under dry conditions. In areas with limited water resources, DI-50 subjects can be recommended in terms of water-saving.