Core Ideas In high‐yielding conditions, biological nitrogen fixation and soil total N may not be sufficient to sustain N uptake rates during soybean seed‐filling period to meet the seed N demand required to reach the maximum attainable seed yield. Foliar N fertilization in R3 to R4 growth stages may be used to increase N supply during the final reproductive cycle of plant. The importance on nutrients application, in special N, in crop production has increased in recent years in tropical and subtropical conditions in Brazil because of intensive cultivation (soybean–wheat, soybean–corn, and soybean–cotton), use of high yielding cultivars, and increasing the cost of production. Nitrogen sources (urea, ammonium nitrate, potassium nitrate, calcium nitrate, and ammonium sulfate) and rates (0, 5, and 10 kg ha−1) have different responses and efficiency index in seed yield, when N foliar applied on soybean leaves at the R3 to R4 growth stages. The response of soybean [Glycine max (L.) Merr.] to foliar N application during pod formation has been inconsistent. The objective of this study over three growing seasons was to evaluate the effects of foliar N sources and rates of application on yield, nutritional status, and yield components of soybean. The treatments consisted of five sources [NO3NH4, CaNO3, KNO3, urea‐[CO(NH2)2], and (NH4)2SO4], two N rates (5 and 10 kg N ha−1), applied at the beginning pod growth stage, and a control (no‐N fertilization). Foliar N generally increased the seed yield, irrespective of the N source and analysis pooled over three growing seasons showed an average seed yield increase of 5.0% (211 kg ha−1) and 6.1% (259 kg ha−1) for the 5 and 10 kg N ha−1 over control, respectively. Neither N rate nor source affected seed size, protein, oil, and nutritional status of leaves or seed. Nitrogen rate affected N use efficiency, but results varied with N sources. These data suggest that foliar N application may increase yield of soybean under certain environmental conditions.

The introduction of cultivars with earlier development and greater productivity has raised questions about the effect of management practices on soybean [Glycine max (L.) Merr] yield in a no‐till (NT) system. The objective of the study was to evaluate the interaction between N fertilization, row spacing, and plant density on photosynthetic index, yield components, yield, and nutritional status of soybean–wheat (Triticum aestivum L.) intercropping. For soybean cultivation, three N rates, three row spacing, and three planting densities were assessed during two growing seasons, while for wheat, 17.5‐cm row spacing and no N fertilization were used. No significant effects of row spacing and plant density were detected. The yields for 0 and 40 kg N ha−1 rates were similar, while applying 20 kg N ha−1 reduced, on average, soybean yield by 14.5%. The planting densities, row spacing, and N rates did not affect wheat yield, or oil and protein content in soybean seeds. Soil temperature (ST), intercellular carbon dioxide concentration (Ci), and intrinsic water use efficiency (IWUE) increased, while plant height, chlorophyll content (CC), and transpiration rate (Trmmol) decreased with increasing spacing of soybean. Plant density changed ST, Ci, chlorophyll content, and stomatal conductance (gs). Leaf tissue analysis indicated adequate nutrient levels in soybean and wheat. The current management practice with 50‐cm row spacing, no N fertilization to complement biological nitrogen fixation (BNF), and 333,000 plants ha−1 is adequate for soybean cultivation, while N supplied from soil organic matter (SOM) and BNF is sufficient to meet requirements of associated wheat crops.

Soybean is one of the most important legume crops in the world. Two greenhouse experiments were conducted to determine the influence of liming and gypsum application on yield and yield components of soybean and changes in soil chemical properties of an Oxisol. Lime rates used were 0, 0.71, 1.42, 2.14, 2.85, and 4.28 g kg −1 soil. Gypsum rates applied were 0, 0.28, 0.57, 1.14, 1.71, and 2.28 g kg −1 soil. Lime as well as gypsum significantly increased grain yield in a quadratic fashion. Maximum grain yield was achieved with the application of 1.57 g lime per kg soil, whereas the gypsum requirement for maximum grain yield was 1.43 g per kg of soil. Lime significantly improved soil pH, exchangeable soil calcium (Ca) and magnesium (Mg) contents, base saturation, and effective cation exchange capacity (ECEC). However, lime application significantly decreased total acidity [hydrogen (H) + aluminum (Al)], zinc (Zn), and iron (Fe) contents of the soil. The decrease in these soil properties was associated with increase in soil pH. Gypsum application significantly increased exchangeable soil Ca, base saturation, and ECEC. However, gypsum did not change pH and total acidity (H + Al) significantly. Adequate soil acidity indices established for maximum grain yield with the application of lime were pH 5.5, Ca 1.8 cmol c kg −1 , Mg 0.66 cmol c kg −1 , base saturation 53%, Ca saturation 35%, and Mg saturation 13%. Soybean plants tolerated acidity (H + Al) up to 2.26 cmol c kg −1 soil. In the case of gypsum, maximum grain yield was obtained at exchangeable Ca content of 2.12 cmol c kg −1 , base saturation of 56%, and Ca saturation of 41%.

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Resumo -Em algumas culturas com carência de B, observou-se menor deposição de lignina nos elementos do xilema, formando paredes finas e pouco resistentes e menor translocação de carboidratos das folhas para outras partes da planta. Com o objetivo de detectar essas alterações anatômicas no xilema de caules extremamente flexíveis de seringueira (Hevea spp.), que apresentavam sintomas de deficiência de B, realizou-se um estudo anatômico comparativo entre plantas com e sem sintomas de deficiência, quanto à espessura das paredes e grau de deposição de lignina e celulose, bem como quanto à concentração de grãos de amido no parênquima do xilema. Não foi observada variação significativa entre a espessura e o grau de deposição de lignina nas paredes dos elementos do xilema de plantas com e sem sintomas. No entanto, plantas com sintomas apresentaram lamela média de espessura muito reduzida, com menor intensidade de coloração, o que reflete a insuficiência de pectato de cálcio, composto responsável pela adesão entre as células e cuja síntese é bloqueada pela carência de boro. A causa da flexibilidade dos caules foi atribuída à menor coesão entre as células.Termos para indexação: Hevea, lignificação, anatomia vegetal, xilema. Relationship between stem flexibility of rubber tree and boron deficiencyAbstract -In some boron deficient crops, less lignin build up has been observed in xylem elements, which have thinner and weaker walls and also a lower translocation of carbohydrates from leaves to other plant organs. In order to detect these anatomical changes in the xylem of very flexible stem of rubber trees (Hevea spp.) displaying boron deficiency symptoms, a comparative anatomical study was made of the wall thickness, the degree of lignin and cellulose deposition as well as starch grain concentration in the wood parenchyma. No difference was found in thickness and lignin deposition in the walls of xylem elements of normal and boron deficient plants. However, the middle lamella of deficient plants was much thinner, with less intensive staining, reflecting a low supply of calcium pectate, which promotes the adhesion between cells and has its synthesis impaired by boron deficiency. The cause of the flexibility was considered to be due to a lower cohesion between cells.

Most tropical soils have high acidity and low natural fertility. The appropriate application of lime and cattle manure corrects acidity, improves physical and biological properties, increases soil fertility, and reduces the use of chemical and/or synthetic fertilizers by crops, such as soybean, the main agricultural export product of Brazil. This study aimed to assess the effects of the combination of the application of dolomite limestone (0, 5, and 10 Mg ha −1 ) and cattle manure (0, 40, and 80 Mg ha −1 ) on grain yield and the chemical properties of an Oxisol (Red Latosol) cultivated with soybean for two consecutive years. The maximum grain yield was obtained with the application of 10 Mg ha −1 of lime and 80 Mg ha −1 of cattle manure. Liming significantly increased pH index, the concentrations of calcium (Ca 2+ ) and exchangeable magnesium (Mg 2+ ), and cation exchange capacity (CEC) of soil and reduced potential acidity (H + + Al 3+ ), while the application of cattle manure increased pH level; the concentrations of potassium (K + ), Ca 2+ , and exchangeable Mg 2+ ; and CEC of the soil. During the 2 years of assessment, the greatest grain yields were obtained with saturation of K + , Ca 2+ , and Mg 2+ in CEC at the 4.4, 40.4, and 17.5 levels, respectively. The results indicated that the ratios of soil exchangeable Ca/Mg, Ca/K, K/Mg, and K/(Ca+Mg) can be modified to increase the yield of soybean grains.