Inoculation methods with Azospirillum brasilense in sorghum cultivation as a sustainable management tool for reducing nitrogen fertilization: Effects on physiology, nutrition, growth, and yield

Abstract

The sorghum crop has been an excellent option for situations where water deficit and low soil fertility conditions pose greater risks for other second-crop cultures, such as corn cultivation in high-risk regions like Western São Paulo. Additionally, sorghum cultivation has contributed to offering multiple uses, including human and animal nutrition and bioenergy production. However, studies are necessary to optimize the sustainable management of the crop, such as research on nutrient management. In this context, nitrogen fertilization is one of the highest costs in the production process of non-leguminous crops, like sorghum. Developing management techniques that minimize the need for chemical N application and improve nutrient utilization in production systems is essential for increasingly sustainable, productive, and less polluting agriculture. Recent research has demonstrated the potential use of the bacterium Azospirillum brasilense to increase the efficiency of applied fertilizers and soil nutrients, primarily through enhanced root growth, in addition to a small contribution to biological nitrogen fixation (BNF), optimizing nutrient management and plant growth in productive systems. Despite several studies conducted on A. brasilense inoculation in various crops, studies on inoculation methods in sorghum cultivation are still scarce. This information is crucial to define crop management strategies and flexible inoculation practices, which could benefit different production systems based on sorghum cultivation as a second crop, fostering increasingly sustainable agriculture. Based on the above, the objective of the present proposal is to evaluate inoculation methods with A. brasilense in sorghum cultivation associated with 100% or 75% of the recommended nitrogen topdressing dose, aiming to optimize growth and development and reduce nitrogen application in grain sorghum through inoculation. The research project will be conducted in the municipality of Dracena - SP, in a typical sandy-textured Ultisol. The experiment will follow a randomized block design with four replications in a 4 × 2 factorial scheme, comprising 8 treatments: 4 forms of inoculation with A. brasilense (control - no inoculation, seed inoculation, furrow inoculation, and broadcast application at the beginning of sorghum vegetative development), associated with 100% or 75% of the recommended nitrogen topdressing dose. The following variables will be evaluated: leaf chlorophyll index (LCI), gas exchange (IRGA), dry mass and nitrogen accumulation in the shoot and root at full flowering, as well as plant height, stem diameter, 100-grain mass, shoot biomass, sorghum grain yield, and nitrogen accumulation in the shoot and grains at the end of the cycle (harvest time).