The continuous development of soybean cultivars aiming at higher yields can result in a demand of N supply higher than the standard inoculation with Bradyrhizobium species. In this context, Azospirillum species, a nitrogen-fixing microorganism found in the rhizosphere of various plant species, may be studied as a way of providing soybean crop with the part of the N it needs. Employing a completely randomized design with four replicates, this study aimed to evaluate the agronomic performance of two different methods of standard inoculation of Bradyrhizobium spp. associated with the co-inoculation with Azospirillum spp. The tested treatments consisted of the absence of N fertilizer and inoculant, full N recommendation, two single inoculations with Bradyrhizobium spp. (in-furrow and seed-applied) combined with an in-furrow application of Azospirillum spp. At R2 growth stage, the nodule number, nodule dry weight, shoot dry biomass and shoot N content were the variables evaluated, whereas at R8 the grain yield, thousand seed weight and grain N content were assessed. The results demonstrated that the co-inoculation of Bradyrhizobium spp. with Azospirillum brasilense is beneficial to soybean yield, mainly using the in-furrow method of application for Bradyrhizobium spp., associated to the in-furrow co-inoculation with Azospirillum spp. Key words: Glycine max, inoculation, nitrogen content, yield.

Corn has shown different degrees of positive response to inoculation with the nitrogen- fixing bacteria of the genera Azospirillum. Part of it has been attributed to the plant genotypic variation, including the root exudates, that are used by the bacteria as energy source. In this study, we grew two corn hybrids that differ for their response to Azospirillum, to investigate the effect of different exudates profiles on the bacteria growth and nitrogenase activity. Employing high performance liquid chromatography, we identified nine amino acids (asparagine, aspartic acid, serine, glutamic acid, valine, phenylalanine, threonine, tryptophan and alanine), six sugars (glucose, sucrose, xylose, arabinose, fructose and galactose) and four organic acids (citrate, malate, succinate and fumarate). The less responsive corn genotype showed reduced plant growth (root volume, shoot dry mass and shoot N content), a lower concentration of Azospirillum cells within the root tissues, a higher content of asparagine and glucose and a reduced amount of metabolites that serve as bacterial energy source (all organic acids + five sugars, excluding glucose). The genotypes did not interfere in the ability of Azospirillum to colonize the substrate, but the metabolites released by the less responsive one reduced the nitrogenase activity.

The aim of this study was to evaluate the effect of industrial seed treatments on the physiological potential of soybean seeds over storage. Four mixtures of agrochemical products in association with two fertilizers were tested. The agrochemical product mixtures were carbendazim/thiram + imidacloprid/thiodicarb; pyraclostrobin, thiophanate-methyl, and fipronil; thiophanate-methyl/fluazinam + bifenthrin/imidacloprid; and metalaxyl-m/fludioxonil + thiamethoxam. The two fertilizers were 7% N, 16% P₂O₅, 0.6% Co, and 2.5% Mo; and 1% Co, 10% Mo, and 7% P₂ O₅. The experiment was carried out in a completely randomized design in a split-plot arrangement in time, with four replications. The treatments were allocated in the plots, while the storage periods (0, 30, 60, 90, and 120 days) constituted the split-plots. The following tests were carried out in each period: first count of germination, germination, accelerated aging, emergence speed index in sand substrate, and final seedling emergence in sand substrate. Seed germination and vigor declined over the storage period, especially after industrial treatment. Pesticide mixtures of a carbendazim/thiram fungicide base and an imidacloprid/thiodicarb insecticide base most impaired seed physiological potential throughout storage, regardless of fertilizer use in the industrial treatment.

This study aimed to compare the results of germination, vigor, and yield of high- and low-vigor soybean seeds submitted to on-farm application of biostimulant with its application via industrial treatment 60 days before sowing. The experimental design was a factorial arrangement of 6 × 2 × 2 (technology × vigor level × strategy of biostimulant application) for the laboratory experiment and of 6 × 2 (technology × strategy of biostimulant application) for the field experiment. Germination, accelerated aging, emergence in sand, seedling dry biomass, and electrical conductivity were assessed in the laboratory, while stand, one thousand-grain weight, and yield were assessed in the field. Biostimulant application in soybean seeds not coated with pesticides did not affect the physiological quality regardless of the application moment (at the day of sowing or at 60 days before sowing). However, when applied in seeds coated with fungicides and insecticides, better results of germination, vigor, and yield were obtained with the on-farm use of biostimulant.

The objective of this work was to investigate the impact of pesticides on the survival of the plant growth-promoting bacteria Azospirillum in the surface of coated seeds as well as in the maize rhizosphere. Our results showed that the greater the time that the bacteria are in contact with the seed surface, the higher the cell mortality. In uncoated maize seeds, inoculation increased bacterial concentration in root tissues and ensured superior plant growth up to 12 hours of Azospirillum contact with the seed surface, while for the coated seeds, a similar performance was observed only up to six hours of exposure.