SUITABILITY OF PLANT GROWTH-PROMOTING BACTERIA TO DECREASE NITROUS OXIDE EMISSIONS: A CASE STUDY IN SUGARCANE

ALFARO J.D.; VALENCIA-MOLINA M. C; FLORES C.; YÁÑEZ YAZLLE, M. F.; ACRECHE M.M.; CHALCO VERA J.E.

Simposio; Global Symposium on Soils for Nutrition; 2022

Sugarcane requires a high amount of synthetic nitrogen (N), generating concern because it is partially lost to the environment as nitrous oxide (N2O), a powerful greenhouse gas. It could be mitigated by enhancing the nitrogen use efficiency (NUE) 1 by using plant growth-promoting bacteria (PGPB) 2, 3. Bacteria could increase sugarcane biomass per unit of available N, allowing a replacement or reduction of synthetic N. This study aims to determine the effect of PGPB on the growth, yield, and N2O emissions compared to traditional N-fertilization in sugarcane. A greenhouse experiment was performed in a soil with a microbial activity 18 to 36% lower than the soil outside the greenhouse (FDA method). Treatments were: Gluconacetobacter diazotroficus strain PAL5 (PAL5); Pseudomonas fluorescens and Azospirillum brasilense strain AZ39 (P+AZ39), each one (PAL5 and P+AZ39) with (+T) and without trace elements; urea (U1); urea with urease inhibitor (U2), both (U1 and U2) incorporated with a dose of 110 kg N ha-1; and a reference treatment without any application (control). Inoculation was performed at planting by immersion of one-bud stalks in inoculant with a concentration of 108 CFU ml-1 (each bacteria) for 10 minutes. A re-inoculation was applied at the N-fertilization moment (59 days after planting; dap) by located irrigation. The effects of these treatments on the initial growth and N2O emissions were assessed. Gas samplings were performed 1 day before and 3, 6, 10, and 28 days after N fertilization by using the static chamber method. In general, inoculation with PGPB increased plant population (p= 0.004) and sprouting rate (p= 0.009) with an interactive effect of trace elements. All treatments with PGPB had a higher mean population of plants than the control 55 dap. At this moment, the percentage of sprouting was as follows: PAL5+T (66.7%) > P+AZ39 (66.3%) > P+AZ39+T (58.2%) > PAL5 (55.2%) > Control (47.4%, average of all treatments without PGPB as fertilization was performed later at tillering). This resulted in coverage percentages (p= 0.007) of 49.1, 42.3, 40.8, 38.9, and 33.4 % for P+AZ39, PAL5+T, P+AZ39+T, PAL5, and control, respectively. Overall, N2O emissions were low and steady; they picked up 10 days after N fertilization for U1 and U2 treatments. The mean of N2O emissions (adjusting a mixed model) for 87 dap were 30.4 ± 3.9, 13.5 ± 9.8, and ≤ 4.5 μg N2O-N m-2 h-1 for U2, U1, and the average of the rest of the treatments, respectively. Although the roles of PAL5 4,5 and P+AZ39 6,7 on N and phosphorus nutrition and plant growth are well recognized, this work is one of the few that studied its effect on N2O emissions 8. However, additional treatments to explore the interaction between reduced rates of synthetic N fertilizer and PGPB will be required 8. Our results suggest that the enhanced initial growth promoted by PGPB without external N could mitigate N2O emissions while maintaining crop yields. Measurements and analyses need to be continued to determine the impact of PGPB on yield components and cumulative N2O emissions.