Inoculation with Plant Growth-Promoting Bacteria and Nitrogen Doses Improves Wheat Productivity and Nitrogen Use Efficiency

Abstract

Wheat is one of the staple foods of the global population due to its adaptability to a wide range of environments. Nitrogen is one of the crucial limiting factors in wheat production and is considered a challenge to food security. Therefore, sustainable agricultural technologies such as seed inoculation with plant growth-promoting bacteria (PGPBs) can be adopted to promote biological nitrogen fixation (BNF) for higher crop productivity. In this context, the objective of the current study was to evaluate the effects of nitrogen fertilization and seed inoculations with Azospirillum brasilense, Bacillus subtilis and A. brasilense + B. subtilis on agronomic and yield attributes, grain yield, grain N accumulation, N use efficiency and applied N recovery in Brazilian Cerrado, which consists of gramineous woody savanna. The experiment was carried out in two cropping seasons in Rhodic Haplustox soil under a no-tillage system. The experiment was designed in a randomized complete block in a 4 × 5 factorial scheme, with four replications. The treatments consisted of four seed inoculations (control-without inoculation, inoculation with A. brasilense, B. subtilis and A. brasilense + B. subtilis) under five N doses (0, 40, 80, 120 and 160 kg ha^-1, applied from urea) at the wheat tillering stage. Seed co-inoculation with A. brasilense + B. subtilis increased grain N accumulation, number of spikes m^-1, grains spike^-1 and grain yield of wheat in an irrigated no-tillage system of tropical savannah, regardless of the applied N doses. Nitrogen fertilization at a dose of 80 kg ha^-1 significantly increased grain N accumulation and number of grains spikes^-1 and nitrogen use efficiency. Recovery of applied N was increased with inoculation of B. subtilis and co-inoculation of A. brasilense + B. subtilis at increasing N doses. Therefore, N fertilization can be reduced by the inclusion of co-inoculation with A. brasilense + B. subtilis in the cultivation of winter wheat under a no-tillage system of Brazilian Cerrado.

Keywords: Triticum aestivum L.; cereal inoculation; grain yield; microorganisms; nitrogen fertilization; nitrogen use efficiency.

Figure 1

Grain N accumulation in 2016 (A) and 2017 (B); nitrogen use efficiency (NUE) in 2017 (C); NUE in 2016 was not significant as a function of N doses and plant growth-promoting bacterial inoculations and co-inoculation. Error bars indicate the standard deviation of the means (n = 4 replications). **: means it is statistically significant by Tukey’s test at probability p ≤ 0.01.

Figure 2

Recovery of applied N in 2016 (A) and 2017 (B) as a function of N doses and plant growth-promoting bacterial inoculations and co-inoculation. Error bars indicate standard deviation of the means (n = 4 replications). * and **: means it is statistically significant by Tukey’s test at probability p ≤ 0.05 and p ≤ 0.01, respectively.

Figure 3

Number of grains spike⁻¹ of wheat as a function of N doses in the 2016 cropping season. Error bars indicate standard deviation of the means (n = 4 replications). **: means it is statistically significant by Tukey’s test at probability p ≤ 0.01.

Figure 4

Heat-map color scale indicating Pearson’s correlation among evaluated parameters of wheat plants in response to N applications and diazotrophic bacteria inoculations in the 2016 (A) and 2017 (B) cropping seasons. X = indicates a non-significant relationship (p < 0.05). Abbreviations: N = grain N accumulation, NUE = N use efficiency, RA_N = recovery applied N, LCI = leaf chlorophyll index, PH = plant height, NSPIKE = number of spike m⁻¹, GSPIKE = number of grain spike⁻¹, 100-G = 100-grain weight, GY = grain yield.