## 2 Materials and Methods
### \({}^{15}\)N-Nitrogen-Use Efficiency  
To estimate \({}^{15}\)N-nitrogen-use efficiency with isotopic techniques of plant, straw, grain, and soil, samples were collected from the \({}^{15}\)N microplots (from the central furrow: an internal area of 0.8 m \(\times\) 1 m, after excluding the edges) [21]. The collection of plant samples was before each fertilization event (45 and 80 days after sowing, in the tillering stage and the milk stage of development, respectively). Straw, grain, and soil samples were collected at harvest from the same internal sampling area of the microplot. The soil was collected at 30 cm depth, dried at room temperature, and sifted with a No. 100 mesh sieve (to achieve a particle size of 0.149 mm). Plant, straw, and grain samples were milled to obtain smaller sample sizes (straw and plant particle size <2 mm, grain particle size <0.3 mm). All \({}^{15}\)N-enriched samples were processed in the Department of Plant Sciences of the University of California, at the Stable Isotope Facility (SIF) in Davis, with a continuous flow Elemental Analyzer coupled with an Isotope Ratio Mass Spectrometer (EA-IRMS). The equipment determined the percentage of \({}^{15}\)N atoms on all samples (plant, soil, straw, and grain; a \({}^{15}\)N-enriched urea sample was used as a control). Then, the NUE in the samples was calculated according to [PERSON] and [PERSON] (1990) [21], obtaining the nitrogen derived from the soil (Ndfs), subtracting the nitrogen derived from the fertilizer (Ndf), from the total N in the sample. In Vitro Assay of the Microbial Consortium Response to Different Rates of N and C (Anmonium Sulfate and Glucose)  
To determine the influence of varying carbon and nitrogen concentrations in the culture medium on the growth of the consortium strains, nine treatments comprising three replicates of three distinct N (ammonium sulfate) and C (glucose) concentrations were established in Elisa plates. Each strain of the bacterial consortium (_Bacillus aphralesii_ subsp. _cabrialesii_ TES\({}^{\text{3T}}\), _Priestia megaterium_ TRQ8, and _Bacillus panlicheniformis_ TRQ65) was inoculated and fermented in individual centrifuge tubes with 15 mL of a synthetic mineral medium, of composition previously mentioned in the preparation of the bacterial consortium for the field application [glucose, 10 g L\({}^{-1}\); KH\({}_{2}\)PO\({}_{4}\), 6.4 g L\({}^{-1}\); K\({}_{2}\)HPO\({}_{4}\), 5.32 g L\({}^{-1}\); (NH\({}_{4}\))\({}_{2}\) SO\({}_{4}\), 4 g L\({}^{-1}\); 0.4 g L\({}^{-1}\) of MgSO\({}_{4}\)-H\({}_{2}\)O; 0.03 g L\({}^{-1}\) of FeSO\({}_{4}\)-7H\({}_{2}\)O; 0.044 g L\({}^{-1}\) of MnSO\({}_{4}\)-H\({}_{2}\)O; and 0.021 g L\({}^{-1}\) of CaCl\({}_{2}\)], at 30 \({}^{\circ}\)C and 180 rpm, for -24 h, until reaching an optical density of -1.0 (630 nm). Then, they were co-inoculated and co-fermented in a flask with 1 L of the synthetic mineral medium at the same conditions as the preinocula. After the optical density reached -1.0, 0.1 mL of the inoculum was added to each well of the Elisa plates. The base conditions of N and C were the original synthetic mineral medium, which was developed and selected due to the observed optimal growth of the microorganisms in the culture medium in those conditions. A total volume of 1 mL of the mineral medium was added to each well to establish the treatments.