Nitrogen use efficiency in corn cropping system under Savannah conditions: effects of inoculation with plant growth promoting bacteria associated with 15N rates

Abstract

Nitrogen (N) fertilization is one of the highest costs in the production process of non-leguminous crops such as corn (Zea mays L.). Developing management practices which minimize the reliance on chemical N inputs are critical for global food security and environmental sustainability. Recent research has shown the potential for utilization of Plant Growth Promoting Bacteria (PGPB) to enhance nutrient use efficiency in non-leguminous cropping systems, reducing N losses to the environment. Microorganisms such as Azospirillum brasilense and Bacillus subtilis, are PGPB known to have a significant effect on the nutrient balance in the soil-plant ecosystem. The mutualism relationship between PGPB, soil microflora, and plants could lead to better plant nutrition and development and increased productivity, while minimizing the needs for external inputs. The objectives of the proposed study are: I) to assess the potential for using PGPB to improve Nitrogen Use Efficiency (NUE) in corn, using 15N isotopic dilution technique; II) evaluate possible evidence of Biological N Fixation (BNF) in corn from inoculations with A. brasilense and/or B. subtilis, using 15N natural abundance isotopic technique (´15N 0); III) determine if the amount of N required for maximum corn production can be decreased or fulfilled by inoculation with PGPB; IV) determine the pathway that describes how PGPB interacts with plants to increase nutritional efficiency and alleviate abiotic stress. The overall hypothesis of this study is that A. brasilense and B. subtilis have the ability to promote plant growth by increasing NUE, nutrients uptake, and reduce a myriad of environmental stresses pertained to water and nutrient imbalances. This hypothesis will be systematically addressed in greenhouse and in field trials at two different sites under Savannah (Cerrado) conditions (Selvíria - low altitude Savannah, Mato Grosso do Sul State and Rio Verde - high altitude Savannah, Goiás State). The treatments tested will be four levels of PGPB, and five N rates applied to each level of PGPB and relative to control. The PGPB levels will be: a) control (check), without inoculation; single bacterial application, mono-association, with the corn plants b) A. brasilense or c) B. subtilis inoculation), and in double bacterial association with corn plants d) A. brasilense + B. subtilis inoculation). The N rates will be (0, 60, 120, 180 and 240 kg N ha-1 as urea labeled with 15N in a side-dress application). The proposed project will shed light on how the PGPB-corn association can help improve NUE, nutrients uptake, and reduce biotic and abiotic stresses. The potential benefits that will arise from this research is lower amounts of chemical fertilizers needed to grow food for an ever-growing global population. In addition, we expect to develop a clear understanding of the biochemical processes taking place under the use of PGPB in corn production systems. (AU)