Impact of municipal wastewaters of Quetta city on some oilseed crops of Pakistan: Effects on biomass, physiology and yield of sunflower (Helianthus annuus L.)

摘要

Impact of municipal wastewaters of Quetta city on two cultivars viz., SF-187 and SH-3322 of sunflower (Helianthus annuus L.) was assessed during 2005 growth season. Wastewaters effluents were not fit for irrigation purposes due to extremely high mineral contents and heavy metals. In addition, effluents were highly alkaline in nature with much higher EC, BOD, COD, SAR, ESP values. Both cultivars of sunflower were grown in pots and received different effluent concentrations (20%:T1; 40%: T2; 60%: T3; 80%: T2; 100%: T5) for their complete growth period. Control (T1) plants were irrigated with normal tap water. Plants grown in effluents treatments showed stunted growth and development from seedling stage to maturity leading to reduced biomass (50-60%) as compared to the control plants which were lush green with more expanded leaves, fresh and dry weights of shoot and roots. Reduced biomass of treated plants was mainly due to altered physiological process. Stomatal conductance,transpiration rate and photosynthesis rates were reduced by approximately 46%, 58% and 64%, respectively in both the cultivars. Photosynthetic pigments (chlorophyll a & b) were also appreciably reduced in different pollutant treatments compared with control. Reproductive growth of sunflower cultivars was drastically affected by the application of sewage waters. Number of seeds per plant in T5-treated plants was reduced by 53-58%, while seed weight was reduced by 65-69% compared with control. 100-seed weight and harvest index was also reduced significantly from 50-54%, and 29-33% respectively in cultivars SF-187 and SH-3322. Present research work has reported remarkably high reductions in biomass and yield of sunflower plants primarily due to reduced performance of physiological attributes of treated-plants irrigated with deteriorating quality of wastewaters effluents. The results are undoubtedly alarming as the untreated municipal wastewater is being used for irrigation purposes to crops and fruit gardens of Quetta city which is a matter of serious concern and a hidden threat to the farmers and ultimately to the country's economy.