Selenium (Se) is considered a beneficial element for plants; however, in high concentrations, it causes negative effects on plant physiology and development. This study reports the first physiological, nutritional, and ultrastructural description of Se toxicity in cowpea growing under field conditions. Selenium was supplied as a foliar application of sodium selenite at varying concentrations (0, 50, 100, 200, 400, 800, 1200, and 1600 g ha −1). An increased yield was observed with the application of 50 g ha −1 Se. Application of concentrations higher than 50 g ha −1 caused leaf toxicity. Increased lipid peroxidation and hydrogen peroxide concentration and reduced total sugars, sucrose, and carotenoid concentration were observed at highest doses tested (1200 and 1600 g ha −1). Applications of more than 50 g ha −1 Se reduced the phloem diameter, caused chlorosis of the leaf blade with a coalescence of lesions, and caused pink salt deposits to appear. Lesions were observed mainly near the trichomes on the adaxial surface of the leaf blade. An analysis of the element distribution with microprobe Xray fluorescence spectrometry (μ-XRF) revealed accumulation of Se, calcium (Ca), potassium (K), copper (Cu), and manganese (Mn) near the primary vein and in the necrotic brown areas of the leaf lesions. In contrast, Na was homogeneously distributed in the leaf tissue.

BACKGROUND Selenium (Se) is a nutrient for animals and humans, and is considered beneficial to higher plants. Selenium concentrations are low in most soils, which can result in a lack of Se in plants, and consequently in human diets. Phytic acid (PA) is the main storage form of phosphorus in seeds, and it is able to form insoluble complexes with essential minerals in the monogastric gut. This study aimed to establish optimal levels of Se application to cowpea, with the aim of increasing Se concentrations. The efficiency of agronomic biofortification was evaluated by the application of seven levels of Se (0, 2.5, 5, 10, 20, 40, and 60 g ha−1) from two sources (selenate and selenite) to the soil under field conditions in 2016 and 2017. RESULTS Application of Se as selenate led to greater plant Se concentrations than application as selenite in both leaves and grains. Assuming human cowpea consumption of 54.2 g day−1, Se application of 20 g ha−1 in 2016 or 10 g ha−1 in 2017 as selenate would have provided a suitable daily intake of Se (between 20 and 55 μg day−1) for humans. Phytic acid showed no direct response to Se application. CONCLUSION Selenate provides greater phytoavailability than selenite. The application of 10 g Se ha−1 of selenate to cowpea plants could provide sufficient seed Se to increase daily human intake by 13–14 μg d−1. © 2019 Society of Chemical Industry

This research was developed to investigate whether inoculation with Azospirillum brasilense in combination with silicon (Si) can enhance N use efficiency (NUE) in wheat and to evaluate and correlate nutritional and productive components and wheat grain yield. The study was carried out on a Rhodic Hapludox under a no-till system with a completely randomized block design with four replications in a 2 × 2 × 5 factorial scheme: two liming sources (with Ca and Mg silicate as the Si source and limestone); two inoculations (control - without inoculation and seed inoculation with A. brasilense) and five side-dress N rates (0, 50, 100, 150 and 200 kg ha−1). The results of this study showed positive improvements in wheat growth production parameters, NUE and grain yield as a function of inoculation associated with N rates. Inoculation can complement and optimize N fertilization, even with high N application rates. The potential benefits of Si use were less evident; however, the use of Si can favour N absorption, even when associated with A. brasilense. Therefore, studies conducted under tropical conditions with Ca and Mg silicate are necessary to better understand the role of Si applied alone or in combination with growth-promoting bacteria such as A. brasilense.

A B S T R A C TIn search of a more sustainable agriculture, the use of beneficial microorganisms has been highlighted, because they are low-cost and can reduce the use of fertilizers and increase grain yield. The present study aimed to evaluate the efficiency of A. brasilense inoculation and the best form and dose of inoculation in maize, measuring the impact on some physical characteristics and on its nutrition. The experiment was conducted in a greenhouse, in Ilha Solteira, SP, Brazil, in a completely randomized design, with four replicates and eight treatments: 1) control; 2) Seed 1x; 3) Seed 2x; 4) Soil 1x; 5) Soil 2x; 6) Leaf 1x; 7) Leaf 2x; 8) Seed 1x + Leaf 1x, respectively representing in each treatment the site and dose of application (1x, dose recommended by the manufacturer; 2x, twice the dose recommended by the manufacturer). No differences were found in any physical characteristics evaluated between treatments; however, for nutrient contents in the leaf tissue, there was effect on Zn content. It was concluded that, regardless of the presence of A. brasilense inoculation, forms or dose (in hybrid DKB 350), in general, there were no improvements in the characteristics evaluated. Doses e formas de inoculação com Azospirillum brasilense na cultura do milho R E S U M O Microrganismos benéficos vem sendo amplamente aplicados na agricultura, por possuírem baixo custo e possibilitarem a redução da utilização de adubos e incrementos na produtividade de grãos. Com o presente trabalho, objetivou-se determinar o efeito de doses e formas de aplicação do inoculante Azospirillum brasilense na nutrição de planta e na produção da cultura do milho. O experimento foi realizado em casa de vegetação, no município de Ilha Solteira, SP, em delineamento inteiramente ao acaso, com quatro repetições e oito tratamentos: 1) Testemunha; 2) Semente 1x; 3) Semente 2x; 4) Solo 1x; 5) Solo 2x; 6) Foliar 1x; 7) Foliar 2x; 8) Semente 1x + Foliar 1x, sendo, respectivamente dentro de cada tratamento, o local e a dose de aplicação (1x, dose recomendada pelo fabricante; 2x, dobro da dose recomendada pelo fabricante). Não foram verificadas diferenças para os tratamentos avaliados, nas características avaliadas, já para as concentrações de nutrientes no tecido foliar, houve efeito somente para o Zn. Concluiu-se que, independente da presença de inoculação, da forma ou da dose de A. brasilense avaliada, no híbrido DKB 350, de modo geral, não houve melhorias nas características avaliadas e na nutrição da cultura do milho.

Alternative management practices are needed to minimize the need for chemical fertilizer use in non-leguminous cropping systems. The use of biological agents that can fix atmospheric N has shown potential to improve nutrient availability in grass crops. This research was developed to investigate if inoculation with Azospirillum brasilense in combination with silicon (Si) can enhance N use efficiency (NUE) in maize. The study was set up in a Rhodic Hapludox under a no-till system, in a completely randomized block design with four replicates. Treatments were tested in a full factorial design and included: i) five side dress N rates (0 to 200 kg ha-1); ii) two liming sources (Ca and Mg silicate and dolomitic limestone); and iii) with and without seed inoculation with A. brasilense. Inoculation with A. brasilense was found to increase grain yield by 15% when N was omitted and up to 10% when N was applied. Inoculation also increased N accumulation in plant tissue. Inoculation and limestone application were found to increase leaf chlorophyll index, number of grains per ear, harvest index, and NUE. Inoculation increased harvest index and NUE by 9.5 and 19.3%, respectively, compared with non-inoculated plots. Silicon application increased leaf chlorophyll index and N-leaf concentration. The combination of Si and inoculation provided greater Sishoot accumulation. This study showed positive improvements in maize growth production parameters as a result of inoculation, but the potential benefits of Si use were less evident. Further research should be conducted under growing conditions that provide some level of biotic or abiotic stress to study the true potential of Si application.

This study aimed to investigate the effect of irrigation with saline water on fruit quality, yield, and plant nutrition of tomato (Lycopersicon esculentum Mill.) cultivars. Tomato cultivation was carried out under protected environment conditions in a double row system with drip irrigation performed according to the demand of the plants. Commercial fruit weight, commercial fruit number, fruit yield, absorption of Ca, N, P, S, K, and Mg were all affected by saline irrigation. The leaf Na concentration and the concentration of total phenolic compounds, total titratable acids, total soluble solids, vitamin C, carotenoids, and flavonoids in the fruits were favored from the increase in irrigation salinity. The Na+ causes a deficiency of Ca, which impairs seed formation in tomato fruits, as Ca is a structural element in the formation of the pollen grain. The Onix genotype had the highest yield, weight, and number of commercial fruits under control and moderate salt stress conditions. Saline water impaired nutrient absorption and improved tomato fruit quality. Under salt stress, tomato plants were able to absorb and translocate large amounts of Na+ to the shoot and even improved the organoleptic quality of fruits, increasing the content of carotenoids, flavonoids, vitamin C, total phenolic compounds, total soluble solids, and total titratable acids of tomato fruits. The clustering analysis was able to show the highest genetic dissimilarity between the group composed of Shanty, Maestrina, and Ipa 6 and the group with Sheena, Totalle, and Pizzadoro under salt stress conditions; also, it evidenced the greater stability of these genotypes.

There is a lack of more comprehensive research defining how much mineral N can be applied as regards the efficiency of BNF to attain high with Azospirillum brasilense, what is a bacterium that stands out for its biological nitrogen fixation (BNF) in corn crops, reaching economically sustainable yields. Moreover, it would be interesting to investigate the use of silicon, which exerts numerous benefits on grasses, especially when the plants are subjected to biotic and abiotic stresses. The aim of this work was to study a synergistic effect between the inoculation with A. brasilense and the application of silicon, thus enabling a higher efficiency of nitrogen fertilization, evaluating the grain yield of irrigated corn in economic terms. The experiment was conducted in Selvíria, MS, Brazil, under a no-till system, on a Latossolo Vermelho distrófico (Oxisol). The experiment was set up as a randomized block design with four replications, in a 2 × 5 × 2 factorial arrangement consisting of two soil corrective sources (dolomitic limestone and Ca and Mg silicate as source of Si); five doses of N (0, 50, 100, 150 and 200 kg ha -1 ); with and without inoculation with A. brasilense. The inoculation makes the corn increase much more profitable, irrespective of N doses and corrective source. The N dose of 200 kg ha -1 with dolomitic limestone, associated with inoculation provided greater grain yield. However, the highest economic return was obtained at the N dose of 100 kg ha -1 , with dolomitic limestone application and inoculation.

Agricultural practices that allow a productive increase in a sustainable manner are becoming increasingly necessary to feed an ever-growing global population. The inoculation with Azospirillum brasilense has the potential to reduce the use of synthetic mineral fertilizers with efficient capacity to promote plant growth and increase nutrition. Therefore, this research was developed to investigate the potential use of A. brasilense to increase the accumulation of macro- and micronutrients and its influence on grain yield, plant height, and spike population in two wheat cultivars (CD1104 and CD150), under irrigated conditions in the Brazilian Cerrado. The study was carried out in a Rhodic Hapludox under a no-tillage system. The experiment was designed in randomized blocks with six replications, arranged in a 2 × 2 factorial scheme: two cultivars (CD150 and CD1104) and two levels of inoculation (control and with A. brasilense). The inoculation with A. brasilense provided greater accumulation of micronutrients in the aerial part of the wheat. In the cultivar CD1104, B and Cu had an accumulation 27.7 and 57.4% higher compared with those of the control without bacteria. In the cultivar CD150, Azospirillum increased the accumulation of B, Fe, and Mn by 43.8, 49.9, and 22%, respectively, and reduced Cu by 21.9%, compared with those of the control. The cultivar CD150 has greater efficiency to accumulate N (+35.5 kg N ha−1) as compared with the cultivar CD1104. Interactions between inoculation and cultivars resulted in greater accumulation of S and K in the shoot of the wheat cultivar CD150, as well greater accumulation of Cu in CD1104. In growth assessments, inoculation or cultivars did not statistically influence wheat grain yield and spike population. Howevere, for plant height, the CD1104 genotype has 13.1% bigger plant height on average than that of the CD150 genotype. Inoculation can contribute more sustainably to wheat nutrition.