Improvement of yield-related traits of spring rapeseed in response to nano-superabsorbent and bio-fertilizers under water deficit conditions

A two-year experiment was performed to evaluate the efficacies of nano-superabsorbent and bio-fertilizers on the field performance of rapeseed under different levels of irrigation in 2018 and 2019. The experiment was arranged as the split-plot factorial based on a randomized complete block design with three replications. Three irrigation levels (I1, I2, I3: irrigation after 70, 120, and 170 mm evaporation from class A pan, respectively) were arranged in main plots and factorial combination of two levels of nano-superabsorbent (0 and 45 kg ha-1) and four levels of bio-fertilizers (control, Azotobacter and Enterobacter, chitosan, and bacteria + chitosan) in sub-plots. The activities of antioxidant enzymes, hydrogen peroxide, osmolytes, and malondialdehyde content were increased under I2 and I3. This reaction led to a decline in leaf water content, membrane stability index, leaf protein content, and yield-related traits. Application of bio-fertilizers especially chitosan + plant growth-promoting bacteria (PGPR) with and without nano-superabsorbent increased antioxidant enzymes activities. Utilization of nano-superabsorbent decreased the activity of these enzymes. The lack of reduction in these traits by application of nano-superabsorbent + bio-fertilizers indicates that the additive effect of chitosan + bacteria is more than the reduction effect of nano-superabsorbent on these enzymes' activity. The utilization of nano-superabsorbent with bio-fertilizers increased these enzymes’ activities through higher nitrogen retention in the soil and increased fertilizer effect. The utilization of chitosan, PGPR, and nano-superabsorbent, especially chitosan + PGPR + nano-superabsorbent, decreased proline content, however, increased soluble sugars, protein, chlorophyll, leaf water contents, and membrane stability index, and consequently, these treatments affected yield-related traits of rapeseed under water stress conditions.