Abstract
Supplementing N fertilizer demand of flooded rice (Oryza sativa L.) crop by integrated means is important area of research
for economical and sustainable agriculture. For present field trial, three soil N rates (60, 90, 120 kg ha−1) were applied to
main plots. Before transplantation to randomized subplots, roots of rice seedlings were dipped for 1 h in water (control),
Azospirillum and Azotobacter in 1:1 ratio (diazotrophs) or diazotrophs + 10−5 M L-tryptophan (L-TRP). Compared with
control of seedling treatment, diazotrophs alone or in combination with L-TRP significantly (P≤0.05) increased straw and
paddy yields at low (60 kg N ha−1) and medium (90 kg N ha−1) rates of N. However, paddy yield was only non-significantly
different between 90 kg N ha−1 with diazotrophs alone and 120 kg N ha−1 with or without diazotrophs. At 90 and 120 kg N
ha−1
, most of the studied plant growth and nutrient accumulation responses were statistically at par between seedling
treatments with diazotrophs and diazotrophs + L-TRP. Nitrogen application was the main factor that influenced N
concentration in plant tissues. However, seedling treatments also significantly increased N and P concentration in rice straw
and grain. Maximum net value of the produce and value-to-cost ratio were achieved with diazotrophic inoculation at 90 kg N
ha−1
. Conclusively, diazotrophic inoculation supplemented N demand of flooded rice by potentially fixing atmospheric N2 and influencing nutrient dynamics in soil.
