Response of some physiological components of cotton to surface and subsurface drip irrigation using different irrigation water levels

This study was carried out to determine the leaf water potential (LWP), stomatal conductance (SC) and leaf area index (LAI) of cotton crop using subsurface drip irrigation (SSDI) and surface drip irrigation (SDI) and different irrigation water levels based on the FAO-56 Penman-Monteith (PM) during the 2016 and 2017 growing seasons. The critical LWPs in vegetative period, flowering stage and boll formation stage in SDI for irigation time were -24, -23 and -24 bar, respectively. Considering the same putting in order for the crop development stages in SSDI-40 cm, those were -23, -23 and -24 bar, respectively. The values of LWP in SSDI-30 cm were the same levels in SSD-40 cm. LWP in the boll formation stage were, in general, lower (bigger in minus numerical number) compared to the first two development stages of the crop. The critical SCs in vegetative period, flowering stage and boll formation stage in SDI were 312.8, 201.8 and 198.9 mmol m-2 s-1, respectively. The values of SC in the same putting in order for the crop development stages in SSDI-30 cm and SSDI-40 cm were 368.8, 182.6 and 221.8 mmol m-2 s-1; and 371.7, 185.9 and 186.8 mmol m-2 s-1, respectively. SC decreased from the vegetative period through generative period of the crop. The SCs increased together with increasing amount of irrigation water and it decreased with increasing water stress conditions. The LAIs were 2.99, 3.11 and 3.45 in SDI, SSDI-30 cm and SSDI-40 cm, respectively. The values of LAI increased from the surface drip irrigation and lower irrigation water level applied through subsurface drip irrigation and highest level of amount of irrigation water. Although some plant physiological indicators such as LWP and SC might be used for irrigation scheduling and irrigation time, these indicators are highly affected by soil water status, temperature, light, air humidity and calibration of the devices used.