Abstract
Sugarcane is a crop of great economic, social, and environmental relevance in Brazil. The country is the largest sugar producer and the second largest bioethanol producer in the world. The goal of this study was to evaluate the efficiency of a sugarcane inoculant composed of five diazotrophic bacterial strains, as well as nitrogen fertilization of two sugarcane varieties. Two experiments were carried out on two varieties using an experimental design composed of complete randomized blocks in a factorial of two varieties and three treatments with four replicates. The treatments can be described as: inoculation with the consortium of five diazotrophic strains, or N fertilization with 120 kg ha−1, and one control treatment. The following parameters were then evaluated: stem yield, accumulation of total dry matter, nitrogen content, quality of the sugarcane juice, and 15N natural abundance on flag-leaves. Inoculation and N fertilization on the Sapucaia plantation promoted increases of stem yield equivalent to 22.3 and 26.5 Mg ha−1 in the RB867515 variety, in comparison to the control, respectively. Inoculation and N fertilizer used for the Coruripe plantation increased stem yield of 38.0 and 42.4 Mg ha−1, respectively, with the RB867515 variety, while RB72454 showed increases of 16.7 and 37.5 Mg ha−1, both compared to the control. Biological nitrogen fixation was not affected by the treatments, however, both treatments increased the total recoverable sugar yield. Benefits from inoculation appeared to promote plant growth due to the plant–bacteria interaction.
Highlights
Sugarcane (Saccharum spp.) is the most important crop for Brazilian production of renewable energy
Various studies to quantify the contribution of biological N2 fixation (BNF) to the crop have shown that approximately 50% of the total N accumulated in plant tissues comes from the air (Boddey et al, 2001; Lima et al, 1987; Urquiaga et al 2012; Yoneyama et al, 1997)
An inoculant composed of five diazotrophic strains was developed, in which the BNF contribution was of approximately 30%, using the SP701143 sugarcane variety grown in pots with inoculated soil containing a consortium of N2-fixing bacteria (Oliveira et al, 2002)
Summary
Soil samples were collected at three points from each experimental area in layers described as 0–15, 15–30, 30–45, and 45–60 cm (depth that contains most of the sugarcane root system). These samples were dried and sieved through a 2 mm mesh sieve. The weighted average of 15N natural abundance in the profiles was calculated through this methodology, since the N content available in the soil decreases according to profile depth, and almost all sugarcane roots are found only to a depth of 60 cm (Urquiaga et al, 2012). Soil δ15 N values which were extracted by reference plants were compared through mean standard error bars
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