Seed inoculation with Azospirillum brasilense and nitrogen fertilization for no‐till cereal production

Abstract

Cereal crops have a high N requirement in a high‐yield environment. However, N use efficiency is still low in agricultural production systems and little is known about the effects of inoculation with Azospirillum brasilense in a high‐yield environment. A field experiment was conducted from 2012 to 2018 with a maize (Zea mays L.)–wheat (Triticum aestivum L.) rotation under a continuous no‐till in southern Brazil. Seeds were inoculated with A. brasilense (strains Ab‐V5 and Ab‐V6) and different levels of N fertilization were used in top dressing. Seed inoculation provided slight changes in N, P, and K concentrations in leaves and grains of maize and wheat. Increasing N input increased the leaf and grain N concentration and the maize and wheat grain yields. Seed inoculation caused varied responses on cereals in different cropping seasons. Wheat was more affected by inoculation in response to N application than maize. Rainfall distribution during the growing seasons possibly interfered on crop responses with inoculation between years and N fertilization levels. Under a similar N input, inoculation resulted in an average increase of 454 kg ha−1 yr−1 of maize and 242 kg ha−1 yr−1 of wheat by applying a higher N rate to the maize and a lower N rate to the wheat. An additional gain of US$409.72 ha−1 (2012–2018) was also achieved using this strategy. Although the possibility of inoculation causing economy with N fertilization in wheat was evident, for maize in rotation with wheat, A. brasilense inoculation was apparently more viable under higher N fertilizer input.

Improving Sustainable Field-Grown Wheat Production With Azospirillum brasilense Under Tropical Conditions: A Potential Tool for Improving Nitrogen Management

“…The verified results agreed with previous findings that A. brasilense inoculation associated with N fertilization management could increase wheat grain yield between 3 and 26% compared to N application without inoculation (Galindo et al, 2017;Munareto et al, 2019;Caires et al, 2020;Galindo et al, 2020). It has been broadly explored that multifaceted microbe-environment-plant interactions shifts with expansion of agronomic response to A. brasilense inoculation (Cassán and Díaz-Zorita 2016), including bacteria and plant genotypes (Bashan and de-Bashan, 2010;Cassán et al, 2020).…”

“…Under field trial evaluations, crop responses to Azospirillum sp. inoculation have been related to harsh environmental conditions (e.g., dryland, limited fertilization and high temperatures), especially during the initial stages of plant growth (Cesari et al, 2019;Caires et al, 2020). In this study, although supplementary irrigation was performed, total rainfall was poor and not well distributed in all the wheat growing seasons (Suppplementary Figures S1A,B).…”

“…to plants is not the major role in plant growth promotion (Cassán et al, 2020). Additional plant growth promoting mechanisms were proposed, such as the production of phytohormones like gibberellins, auxins and cytokinins (Fukami et al, 2018), increases in root development leading to greater nutrient and water acquisition (Caires et al, 2020), increase in N use efficiency from applied N-fertilizer (Galindo et al, 2020), enhancement of nitrate reductase activity (Fereira et al, 1987;Pereira-Defilippi et al, 2017), solubilization of phosphates (Rafi et al, 2019), among others. Therefore, the additive hypothesis best addresses A. brasilense operating principle, in which multiple mechanisms of plant growthpromotion works in convergence or in sequence (Bashan and de-Bashan 2010;Cassán et al, 2020).…”

“…It has been reported that inoculation with A. brasilense can generate an economy of 1.2 billion dollars per year with half substitution of N-based fertilizer application required by wheat and maize crops (Hungria et al, 2010). Similarly, Caires et al (2020) concluded that since wheat seed inoculation A. brasilense has demonstrated economic viability, the strategy of side-dressing N application could be changed and a lower N level may be applied to wheat crops. For instance, it should be also highlighted that the obtained results should be carefully considered for the specific conditions tested (no-till, specific N fertilizer type, environmental conditions, wheat cultivar etc.)…”

“…To date, the additive hypothesis best addresses A. brasilense operating principle, in which multiple mechanisms of plant growth-promotion works in convergence or in sequence (Bashan and de-Bashan 2010;Cassán and Diaz-Zorita 2016;Cassán et al, 2020). For example, A. brasilense has been reported to promote plant growth by increasing the production of phytohormones like gibberellins, auxins and cytokinins (Fukami et al, 2018), increasing root development leading to greater nutrients and water acquisition (Caires et al, 2020), increasing N use efficiency from applied N-fertilizer (Galindo et al, 2020), enhanced nitrate reductase activity (Ferreira et al, 1987;Pereira-Defilippi et al, 2017), solubilization of phosphates (Rafi et al, 2019), among others. Although the adoption of A. brasilense inoculation by Brazilian farmers has increased in recent years, it is not yet a consolidated management practice in agricultural production systems such as Bradyrhizobium sp.…”