The survival of Azospirillum brasilense Cd and Sp-245 in the rhizosphere of wheat and tomato plants and in 23 types of plant-free sterilized soils obtained from a wide range of environments in Israel and Mexico was evaluated. Large numbers of A. brasilense cells were detected in all the rhizospheres tested, regardless of soil type, bacterial strain, the origin of the soil, or the amount of rainfall each soil type received prior to sampling. Survival of A. brasilense in soils without plants differed from that in the rhizosphere and was mainly related to the geographical origin of the soil. In Israeli soils from arid, semiarid, or mountain regions, viability of A. brasilense rapidly declined or populations completely disappeared below detectable levels within 35 days after inoculation. In contrast, populations in the arid soils of Baja California Sur, Mexico, remained stable or even increased during the 45-day period after inoculation. In soils from Central Mexico, viability slowly decreased with time. In all soils, percentages of clay, nitrogen, organic matter, and water-holding capacity were positively correlated with bacterial viability. High percentages of CaCO 3 and fine or rough sand had a highly negative effect on viability. The percentage of silt, pH, the percentage of phosphorus or potassium, electrical conductivity, and C/N ratio had no apparent effect on bacterial viability in the soil. Fifteen days after removal of inoculated plants, the remaining bacterial population in the three soil types tested began to decline sharply, reaching undetectable levels 90 days after inoculation. After plant removal, percolating the soils with water almost eliminated the A. brasilense population. Viability of A. brasilense in two artificial soils containing the same major soil components as the natural soils from Israel did was almost identical to that in the natural soils. We conclude that A. brasilense is a rhizosphere colonizer which survives poorly in most soils for prolonged periods of time; that outside the rhizosphere, seven abiotic parameters control the survival of this bacterium in the soil; and that disturbance of the soil (percolation with water or plant removal) directly and rapidly affects the population levels. Azospirillum species survive for prolonged periods of time in the rhizosphere of numerous plant species (13). Colonization of roots is nonspecific, and bacteria migrate between different plant species (7, 9, 18). However, conflicting evidence has been reported for survival of Azospirillum spp. in the soil outside the rhizosphere. Azospirillum spp. occur in most soils of tropical (3, 22, 23, 48, 51) and some soils of temperate (26) regions, indicating a high survivability outside the rhizosphere. In contrast, in studies done mainly in temperate and semiarid zones (1, 4, 15, 21, 52, 53), but also in tropical regions (41), it was found that introduced Azospirillum spp. survived poorly in these soils and hardly lasted from one season to the next (27). In Israeli soils, Azospirillum spp. adsorbed firmly ...

The present research was aimed at the foliar biofortification of chard plants with iron and selenium and at determining the influence of this treatment on the accumulation of these elements, as well as proteins and nitrate, in the aerial portion (shoot) of chard. A 3 2 factorial experiment was conducted for the above purpose, and the study factors were the foliar applications of Fe (0, 2500 and 5000 mg L -1 ) and Se (0, 10 and 20 mg L -1 ). The foliar applications were performed every 15 days for a total of four spray applications. The variables evaluated were the accumulations of Fe, Se, proteins, and nitrate in the shoot. Two samples were collected after performing the second and fourth foliar spray applications. The results indicate that increasing application concentrations of Fe and Se promote greater foliar accumulations of these elements. Foliar applications of Se did not affect the accumulation of nitrate; however, a greater foliar accumulation of Se produced a greater accumulation of proteins. On the other hand, after only four foliar spray applications of Fe at a dose of 5000 mg L -1 , there was a statistically significant accumulation of nitrate, which had a positive correlation with the lower accumulation of proteins.

Summary In the quantification and analysis of the distribution of soil basic components, factors such as spatial resolution, scales of observation and analytical techniques used to interpret digital images of microscopic platforms are critical to obtain reproducible results. In addition, individual or discrete images, sometimes with high spatial resolution, distort features or basic components when zooming in or out, which limits their classification. This research proposes the use of micromorphological tools, spatially referenced mosaics with high resolution, image analysis and composite images to elaborate thematic maps of soil components. Therefore, we created mosaics with sequential digital images from soil thin sections (up to 3850 mm2) of different diagnostic horizons, with different magnifications (2×, 10× and 20×) and light sources. The mosaics (between 0.25 and 2.6 μm2 per pixel, and between 2 and 8 GB file size) were processed by image analysis (segmentation, supervised classification and accuracy assessments) for delimiting their basic soil components from composite images and with spatial operators to elaborate thematic maps at the microscopic level. The RGB (red, green, blue) brightness values of each soil component with different light sources enabled us to identify and quantify size classes of aggregates, voids, pedofeatures and organic matter with different degrees of decomposition at a high level of precision (up to 99% overall accuracy). It was also possible to develop good‐quality thematic maps of such components from high‐resolution spatially referenced mosaics and composite images Thematic maps of soil components can be explored without losing their spatial reference and analysed on multiple scales from a whole soil thin section. Highlights Micromorphology and digital cartography to develop thematic maps of soil components High spatial resolution mosaics from thin sections and image analysis were used for mapping RGB brightness values of different light sources facilitated mapping of soil features Accurate maps enabled quantification and analysis of spatial relations of soil components

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