ABSTRACT:The biological nitrogen fixation (BNF) process in grasses is caused by diazotrophic bacteria, particularly Azospirillum brasilense. However, studies are lacking on BNF efficiency to define how much mineral nitrogen (N) can be applied to achieve more sustainable high yields. Furthermore, there should be an analysis of whether urea with the urease enzyme inhibitor NBPT is less harmful, benefiting BNF in grasses. The objective of this study was to evaluate the effect of N sources and N rates associated with inoculation with Azospirillum brasilense regarding foliar diagnosis and leaf chlorophyll index (LCI), agronomic efficiency (AE), and corn grain yield in the Cerrado (Brazilian tropical savanna) region. The experiment was conducted in a no-tillage system in a Latossolo Vermelho Distroférrico (Oxisol). A randomized block experimental design was used with four replications in a 2 × 5 × 2 factorial arrangement as follows: two N sources -urea and Super N, urea with urease enzyme inhibitor NBPT [N -(n-butyl thiophosphoric triamide)]; five N rates (0, 50, 100, 150, and 200 kg ha -1 ) applied in topdressing; and two seed inoculation treatments, one with and one without A. brasilense. N rate positively influenced the LCI and concentrations of N, S, and Mn in leaves, and may increase the concentrations of P, Cu, and Fe; however, higher N rates can reduce AE. The N sources had similar effects, and therefore urea is recommended for N fertilization. Inoculation with A. brasilense decreased leaf concentration of Fe and increased LCI, leaf concentration of P, AE, and corn grain yield; the use of this diazotrophic bacterium is therefore viable even when high rates of N are applied.

Manganese (Mn) is an essential element for plants; however, high concentrations in certain soil conditions can cause toxicity symptoms in the plant tissue. Here, we describe Mn toxicity symptoms and Mn toxicity responses in soybean plants. Soybean plants exposed to excess Mn showed reductions in the CO assimilation rate and stomatal conductance, which in turn resulted in decreased shoot biomass. Furthermore, peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activity were higher in plants grown with the highest Mn concentration. The Mn doses increased the activity of antioxidant enzymes such as CAT, POD, and SOD. The toxicity symptoms presented by the leaves included hypertrophying of the adaxial epidermis and the formation of necrotic areas with purple-colored veins. Dramatic movement of calcium from the healthy region to the purple-colored necrotic region was observed, as was the exit of potassium from the necrotic area to the healthy region of the tissue. The high activities of POD and SOD in the presence of high Mn compartmented in the roots was the main physiological responses at high Mn uptake by soybean plants.

RESUMONeste trabalho, objetivou-se comparar épocas e doses de aplicação do superfosfato triplo (SFT) cloreto de potássio (KCl) com e sem revestimento por polímero no desempenho produtivo da soja em condições edafoclimáticas de cerrado. O experimento foi realizado em Rio Verde, GO, em um Latossolo Vermelho distroférrico. Os tratamentos foram dispostos em delineamento de blocos ao acaso, em esquema fatorial 2x2x2+1. O primeiro fator foi constituído pelos fertilizantes SFT e KCl revestidos ou não por polímeros, o segundo por duas doses de fósforo e potássio (40 + 40 e 80 + 80 kg ha -1 P 2 O 5 e K 2 O), e o terceiro, por duas épocas de aplicação dos fertilizantes (15 dias antes da semeadura e na semeadura). Inclui-se ainda, um tratamento testemunha sem adubação. Foi avaliada a produção de biomassa, a produtividade de grãos e componentes de produtividade. Houve resposta à aplicação da adubação com P e K na produção de massa fresca e produtividade, sendo a ausência de adubação prejudicial ao desenvolvimento da cultura da soja. A aplicação a lanço de superfosfato triplo e cloreto de potássio, revestidos por polímeros 15 dias antes da semeadura, proporcionou maior produção de massa seca, número de vagens por planta e produtividade de grãos de soja em relação aos fertilizantes convencionais. Quando aplicados na semeadura, os fertilizantes convencionais e fertilizantes revestidos por polímeros conferiram a mesma produção de massa seca e produtividade de grãos de soja. Termos para indexação:Glycine max, fertilizante de liberação controlada, nutrição de plantas. ABSTRACTThe objetive of this work was to compare times and application rates of triple superphosphate (TSF) and potassium chloride (KCl) with and without polymer coating on soybean yield performance in the cerrado environmental conditions. The experiment was conducted in Rio Verde, GO, in an Oxisol. Treatments were arranged in a randomized block design, in factorial 2x2x2+1. The first factor consisted by fertilizer TSF and KCl coated or not by polymer, the second by two doses of phosphorus and potassium (40 + 40 and 80 + 80 kg ha -1 P 2 O 5 and K 2 O, respectively), and the third by two times of application fertilizer (15 days before sowing and at sowing). It also includes a treatment control without fertilization. Biomass yield, grain yield and yield components were evaluated. There was a response to the application of fertilizer P and K in fresh mass production and productivity, with the absence of fertilizer detrimental to the development of soybean. The broadcast application of superphosphate and potassium chloride coated polymer 15 days before sowing promoted dry matter yield, number of pods per plant and grain yield of soybeans compared to conventional fertilizer. When applied at sowing, the conventional fertilizer and slow release fertilizers promoted the same dry matter yield and grain yield of soybeans.

-The objective of this work was to evaluate the effect of inoculation with Azospirillum brasilense, associated with N rates and sources, in soil of the Cerrado (Brazilian savanna), on the grain yield of irrigated wheat (Triticum aestivum). The experiment was carried out under a no-tillage system in a Typic Haplustox. The experimental design was randomized complete blocks with four replicates, in a 2x5x2 factorial arrangement: two N sources (urea and urea with NBPT urease inhibitor); five N rates applied as topdressing (0, 50, 100, 150, and 200 kg ha -1 ); and with or without seed inoculation with A. brasilense. The increase in the N rates positively affected spike length, number of spikelets and of grains per spike, number of spikes per meter, N accumulation in the straw, leaf chlorophyll content, and grain yield of irrigated wheat, regardless of the use of NBPT urease inhibitor with conventional urea. Singly, inoculation with A. brasilense does not affect production components and grain yield, despite the increase in N content in wheat straw. The inoculation with A. brasilense, associated with the application of 140 kg ha -1 N, provides the highest grain yield of irrigated wheat cropped after corn in low-altitude Cerrado.

New studies are needed to optimize the nitrogen amount that can be applied to utilize the Azospirillum brasilense benefits in maize cropping systems. In addition, information regarding the interaction between the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and biological nitrogen fixation (BNF) and how they affect the crop development and yield is also needed. The objective of this study was to evaluate the effect of rates and sources of N in combination with A. brasilense, on leaf chlorophyll index (LCI), N leaf concentration, production components, and maize grain yield in the Brazilian Cerrado region. The study was performed in a Typic Rhodic Hapludox under no-tillage system. The experimental design was a randomized complete block design with four replications arranged in a 2 × 5 × 2 factorial scheme: two N sources (urea and urea with NBPT) and five N rates (0, 50, 100, 150, and 200 kg ha-1), with and without A. brasilense inoculation. The increase in N rates significantly enhance LCI, N leaf concentration, plant height, ear diameter, mass of 100 grains, and grain yield. No significant differences were observed among the N sources. Inoculation with A. brasilense increased LCI, stem diameter, ear length, and nitrogen use efficiency (NUE), with a positive effect on grain yield. The increase in N rate up to 200 kg ha-1 with A. brasilense inoculation increased grain yield, independently of the N source. The application of 100 kg ha-1 of N as urea, with inoculation of A. brasilense produced the highest profit in maize production.

Nickel (Ni) toxicity has been reported to decrease productivity in soybean (Glycine max L.). However, soybean responses to Ni toxicity are not well understood. The aim of the present study was to describe Ni toxicity in soybean plants through physiological, nutritional, and ultrastructural analyses. Plants were grown in nutrient solution containing increasing Ni concentrations (0, 0.05, 0.1, 0.5, 10, and 20 μmol L −1), and nutritional, anatomical, physiological and biochemical features were determined. The results revealed previously unreported detrimental effects of Ni toxicity on soybean plants. CO 2 assimilation rates, stomatal conductance and transpiration decreased, resulting in lower biomass in soybean plants exposed to the highest Ni levels. Nitrate reductase activity increased with up to 0.05 μmol L −1 Ni and then decreased, indicating halted N-metabolism. Urease activity increased with increasing Ni availability in the nutrient solution, and peroxidase and superoxide dismutase activities were higher in plants grown at higher Ni levels. Leaf epidermal thickness (abaxial and adaxial), as well as root xylem and phloem diameter, decreased starting at 0.1 μmol L −1 Ni. Mean Ni concentrations varied from 77.5 to 17,797.4 mg kg −1 in roots and 2.3 to 16,774.5 mg kg −1 in shoots. Soybean plants exhibited symptoms of Ni toxicity starting at 0.1 μmol L −1 Ni, presenting mean shoot Ni concentration of 28.9 mg kg −1 , along with leaf water loss until complete drying. The results contribute to our understanding of several physiological, biochemical and histological mechanisms of Ni toxicity in soybean, which is still poorly understood.

Azospirillum brasilense is a bacterium known for its biological nitrogen fixation (BNF) in corn crops. However, there is a lack of comprehensive research defining how much mineral N should be applied to maximize the efficiency of BNF and attain high, economically sustainable yields. Moreover, it would be interesting to investigate whether adding urea with NBPT urease inhibitor might increase BNF in grasses. Therefore, the aim of this study was to determine the effect of inoculation with Azospirillum brasilense associated with N sources and doses in a Cerrado biome soil by 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 sources of N (urea and urea with NBPT urease enzyme inhibitor) and five N doses applied as top-dressing (0, 50, 100, 150, and 200 kg ha -1 ), with and without the inoculation of seeds with A. brasilense. Inoculation with Azospirillum brasilense makes corn growth much more profitable, irrespective of the dose and source of N. Addition of 200 kg ha -1 N in the form of conventional urea coupled with inoculation with Azospirillum brasilense increases grain yield; however, the highest economic return is obtained with N applied at 100 kg ha -1 with conventional urea and inoculation. Key words: Fertilizer with improved efficiency. Nitrogen fertilization. No-tillage system. Total operational cost. Urea. Zea mays. ResumoO Azospirillum brasilense se destaca na fixação biológica de nitrogênio (FBN) em cultivo de milho. Contudo, faltam maiores pesquisas para definição do quanto se pode aplicar de N mineral quanto à eficiência da FBN, para alcançar altas produtividades economicamente sustentáveis. Além disso, seria interessante analisar se a ureia com inibidor da enzima urease NBPT pode ser menos prejudicial, beneficiando a FBN em gramíneas. Sendo assim, objetivou-se estudar o efeito da inoculação com Azospirillum brasilense, associado às doses e fontes de N, em solo de Cerrado, avaliando economicamente a produtividade de grãos de milho irrigado. O experimento foi desenvolvido em Selvíria -MS, em sistema plantio direto, em Latossolo Vermelho distrófico. O delineamento experimental foi em blocos

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.