Precursor (L-tryptophan)-Inoculum (Azotobacter) Interaction for Improving Yields and Nitrogen Uptake of Maize

Auxins produced in the rhizosphere as a result of precursor-inoculum interaction may affect plant growth. Auxin production by Azotobactercultures was measured {in vitro} in the presence and absence of L-tryptophan and the most prolific auxin-producing culture (Z4) was then selected. A field experiment was conducted to evaluate the effect of L-tryptophan (an auxin precursor) and Azotobacterapplication on the growth, yield, and nitrogen (N) uptake of maize crop. Five levels of L-tryptophan (10− 3–10− 7 M) were tested with and without Azotobacter inoculation in a fertilized (NPK: 150–100–100 kg ha− 1, respectively) field. Results revealed that application of L-tryptophan (L-TRP) or Azotobacter inoculation alone significantly affected the maize crop; however, their combined application produced more pronounced effects as compared with their separate application. Combined application of 10− 4 M L-TRP and Azotobacter significantly increased the grain yield (18.4%), fresh biomass (16.7%), 1000-grain weight (14.5%), and total nitrogen uptake (40%) compared with an untreated and uninoculated control. It is highly likely that the physiological response evoked is due to the presence of auxins produced in the rhizosphere of maize as a result of precursor-inoculum interaction.