Co-applied Nitrogen and Auxin via Nano-clay-Polymer Composites Enhances Yield and Nitrogen Use Efficiency

Simultaneous application of nitrate (NO3⁻-N) and synthetic auxin in nano-clay-polymer composites (NCPC) is hypothesized to increase rice yield and nitrogen (N) use efficiency. A pot experiment was conducted in 2019 at ICAR-National Rice Research Institute (NRRI), Cuttack, Odisha, India, during Rabi season with rice variety Sahbhagi dhan with eight treatments, viz. control, auxin 1-naphthaleneacetic acid (NAA), sodium nitrate (NaNO3), NAA + NaNO3, NCPC, NCPC + NAA, NCPC + NaNO3 and NCPC + NAA + NaNO3, in four replicates using a basal addition of ${}^1/{}_3$ of the recommended dose, i.e. 35.71 mg N kg⁻¹. Except for the control, urea was applied to all the treatments at maximum tillering and panicle initiation stages using one-third of the recommended N dose at each stage without further addition of NAA or NCPC. Phosphorus and potassium were added at the rate of 17.86 mg kg⁻¹ in all pots (including control). Plant yield increased more in NCPC-loaded NaNO3 fertilizer treatments than the NaNO3 fertilizers alone. Combined application of NaNO3 and NAA loaded in NCPC resulted in the highest yield, which was 71%, 43% and 28% higher than the control, sole application of NAA and sole application of NaNO3, respectively. Combined application of NCPC, NaNO3 and NAA was found to have 7.6% higher total N content in grain than the NaNO3 alone. Although the pH and electrical conductivity remained unchanged among all treatments, it was found that soil available N (175 mg kg⁻¹) and N uptake in straw and grain were highest in the NCPC + NAA + NaNO3 treatment. Hence, we conclude that smart delivery of NO3⁻-N and synthetic auxin through NCPC offers significant benefits in terms of yield, N content and N use efficiencies in rice.