Waste water irrigation in the regulation of soil properties, growth determinants, and heavy metal accumulation in different Brassica species.

To evaluate the impact of waste water (WW) irrigation, four Brassica species, namely B. campestris, B. juncea, B. napus, and B. nigra, were grown for 2 years in the agricultural field. First-year experiment (2014-2015) was conducted with the comparative effect of WW and ground water (GW) under a uniform dose of NPK (N80P45K45, kg ha-1). WW irrigation proved efficacious over GW to increase growth, physiological, and yield parameters. Increase in all parameters was due to the use of WW which leads to the improvement in the physico-chemical properties of soil as compared to resulted soil from GW application. Second-year experiment (2015-2016) therefore deals with WW irrigation only but under interaction with two levels of NPK fertilizers (N80P45K45 and N60P30K30, kg ha-1). Results of this year revealed that maximum enhancement in growth, physiological, and yield parameters was observed at WW × N60P30K30 and the input of WW × N80P45K45 was not of benefit. WW × N60P30K30 treatment was beneficial also because, at this treatment level, the accumulation of Cr, Cu, Pb, Ni, and Cd in leaf and seed was comparatively lesser in amount than that of WW × N80P45K45. The study concluded even though the use of WW was applicable to save freshwater, enhance soil nutrient status, and make N, P, and K balance at their lower inputs, WW irrigation caused accumulation of heavy metals in all Brassica crops far above the safe limits during a quite longer irrigation time (70 days and 105 days after sowing (DAS)). However, WW was safe to use only up to 35 DAS. Therefore, the study suggested that there should be regular monitoring of heavy metal concentrations in irrigation water as well as in various crop vegetables.