Impact of municipal waste water of Quetta city on biomass, physiology and yield of canola (Brassica napus L.)

The present study was carried out in order to investigate the impact of municipal wastewater effluents of Quetta city on the biomass, physiology, and productivity of two canola (Brassica napus L.) cultivars viz., Oscar and Rainbow. Plants were grown in pots from seed to maturity during 2005-2006 growth seasons. Different concentrations of effluents (T1: 20%; T2: 40%; T3: 60%; T4: 80; T5: 100%) were supplied to plants as a soil drench compared to control plants (T0) receiving normal tap water. The wastewater effluents were highly alkaline in nature along with very high Electrical Conductivity, Biological Oxygen Demand; Chemical Oxygen Demand; Sodium Adsorption Ratio, Total Suspended Solids and minerals concentrations have found well above threshold limits set for the usage of municipal wastewater for irrigation purposes. Growth performance of both canola cultivars showed statistically significant effects on some physiological attributes. All treated plants showed reductions in growth and yield parameters, but T5 treated plants were most affected compared to control. There were significantly higher reductions in stomatal conductance (49% in Oscar; 53% in Rainbow), transpiration rate (62% Oscar; 67% in Rainbow), and photosynthetic rate (62% in Oscar; 69% in Rainbow) of T5 treatment plants compared with control. Both pigments of chlorophyll (a & b) responded efficiently to the applied stress of wastewater effluents showing reductions in chlorophyll a and b by 68-82% in cv. Oscar and 74-86% in cv. Rainbow. Similarly, fresh and dry biomass also showed reductions in different effluents treated plants (T1 to T5) ranging from 2-78% in both the cultivars of canola. Drastic reductions were recorded in the number of siliqua per plant (70-72%), seeds per plant (84-85%), seed weight per plant (87-90), and in the harvest index (72-74%) in cultivars Oscar and Rainbow, respectively than that of control. The overall result of the municipal wastewater impacts on canola cultivars are alarming, as Pakistan is an agrarian country and the agriculture sector bears the brunt of country's economy. This study urged the vital significance of recycling the liquid wastewater effluents before discharge otherwise these could seriously affect the growth and productivity of plants.