Inoculation with Herbaspirillum seropedicae associated with nitrogen (15N) fertilization on marandu grass

Author(s)

Cássio Carlette Thiengo

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2023-03-08

Examining board members

José Lavres Junior; Fernando Shintate Galindo

• Advisor: José Lavres Junior

Abstract

The compatibility between four levels of nitrogen fertilization (N-urea) was evaluated in marandu grass (Urochloa brizantha cv. Marandu) inoculated by leaf application with emerging endophytic diazotrophic bacteria (Herbaspirillum seropedicae HRC54). The experiment was developed under a randomized block design under greenhouse conditions, following a 4x2 factorial scheme. This approach was based on the recurrent environmental and economic appeal around the low use efficiency of N-urea in non-legume crops. More usual procedures in our field of research were combined with precise techniques to address the contribution of N-fixed and the recovery of applied N-fertilizer in this plant-bacteria interaction primarily. A combination of 15N isotopic techniques (natural abundance &#948;15N and isotopic dilution) found that inoculation contributed significantly to N-fixed, but a substantial reduction in biological nitrogen fixation was observed with increasing N levels (from 21.5% to 8.6%). At a high N-fertilization level (100 mg kg-1of soil), little or no effect of inoculation was found, providing the sufficient basis to classify it as inhibitory to microorganism action. Inoculated marandu grass plants provided with more modest N-fertilization conditions (default, low and medium level or 0, 25, and 50 mg kg-1 soil, respectively) produced more root (up to +37.7%) and shoots (up to +28.5%) dry matter. They also exploited more soil resources (N, P, K, Mg, and Fe were accumulated more in shoots) as well as applied N-fertilizer (recovering up to 2 times more), which was attributed mainly to the more significant development of smaller diameter roots (especially <1mm). Here, we communicate, on a small scale, how to take better advantage of H. seropedicae inoculation on marandu grass, thus contributing to more rational and efficient N-fertilizer use. Finally, we open questions for further investigations based on 15N isotopic techniques with great potential for applicability. (AU)

• FAPESP's process: 21/05372-0 - Inoculation of Herbaspirillum seropedicae associated with nitrogen (15N) fertilization on marandu physiological and biochemical changes and recovery of applied N
• Grantee: Cássio Carlette Thiengo
• Support Opportunities: Scholarships in Brazil - Master