Essential plant nutrients are mainly applied to soil and plant foliage for achieving maximum economic yields. Soil application method is more common and most effective for nutrients, which required in higher amounts. However, under certain circumstances, foliar fertilization is more economic and effective. Foliar symptoms, soil and plant tissue tests, and crop growth responses are principal nutrient disorder diagnostic techniques. Soil applications of fertilizers are mainly done on the basis of soil tests, whereas foliar nutrient applications are mainly done on the basis of visual foliar symptoms or plant tissue tests. Hence, correct diagnosis of nutrient deficiency is fundamental for successful foliar fertilization. In addition, there are some more requirements for successful foliar fertilization. Foliar fertilization requires higher leaf area index for absorbing applied nutrient solution in sufficient amount, it may be necessary to have more than one application depending on severity of nutrient deficiency. Nutrient concentration and day temperature should be optimal to avoid leaf burning and fertilizer source should be soluble in water to be more effective. Foliar fertilization of crops can complement soil fertilization. If foliar fertilization is mixed with postemergence herbicides, insecticides, or fungicides, the probability of yield response could be increased and cost of application can be reduced.

and urea are main sources of nitrogen (N) for annual crop production in developing countries. Two greenhouse experiments were conducted using ammonium sulfate and urea as N sources for upland rice grown on a Brazilian Oxisol. The N rates used were 0, 50, 100, 150, 3000, and 400 kg N kg −1 of soil. Yield and yield components were significantly increased in a quadratic fashion with increasing N rate. Ammonium sulfate X urea interaction was significant for grain yield, shoot dry matter yield, panicle number, plant height and root dry weight, indicating a different response magnitude of these plant parameters to two sources of N. Based on regression equation, maximum grain yield was achieved with the application of 380 mg N kg −1 by ammonium sulfate and 271 mg N kg −1 by urea. Grain yield and yield components were reduced at higher rates of urea (>300 mg kg N) but these plant parameters' responses to ammonium sulfate at higher rates was constant. In the intermediate N rate range (125 to 275 mg kg −1 ), urea was slightly better compared to ammonium sulfate for grain yield. Grain yield was significantly related with plant height, shoot dry weight, panicle number, grain harvest index and root dry weight. Hence, improving these plant characteristics by using appropriate soil and plant management practices can improve upland rice yield.

Amazonas State is the largest state in Brazil and mainly covered by tropical forest. Because of the importance of the tropical forest in maintaining soil health and a clean environment, conservation of the Amazon forest is a national priority. However, sustainable agriculture development is necessary in the state for the welfare of the local population. Maintaining soil fertility at an adequate level is an important component of sustainable farming. Very little information is available about soil fertility of Amazonas State. The objective of the present study was to evaluate chemical soil properties of Amazonas State of Brazil. Results include chemical properties of 3,340 samples, covering 62 municipalities of the state collected at 0-20 cm deep during 30 years . Chemical properties [phosphorus (P), potassium (K) extracted with Mehlich 1, calcium (Ca), magnesium (Mg), aluminum (Al) extracted with potassium chloride (KCl) 1.0 mol L 21 , potential acidity (H + Al) extracted with calcium acetate, and base saturation] presented great variation, except cation exchange capacity (CEC) and pH (water). Most of the soil samples were characterized as having high acidity; medium level of organic-matter content; low levels of P, K, Ca, and Mg; and high levels of Al and H + Al. Overall, base saturation was less than 20%, a value considered very low for most of annual crops. Soils from upland areas were more acidic and have poor fertility compared with lowland soils. To maintain sustainability of cropping systems, use of an adequate level of liming and chemical fertilizers are necessary on these soils.

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.

Rhizobia and other plant growth‐promoting rhizobacteria (PGPR) have been broadly used as inoculants in agriculture, resulting in morphofunctional improvements in roots and grain yield. This study was carried out during two cropping seasons under field and greenhouse conditions in Brazil to verify the effects of inoculation of two soybean cultivars with PGPR and secondary microbial metabolites (SMMs) on root activity and nodulation, plant development, and grain yield. Inoculation and co‐inoculation treatments consisted of Bradyrhizobium japonicum strain SEMIA 5079 and B. diazoefficiens strain SEMIA 5080 inoculated together, in combination with Bacillus subtilis strain QST 713, Azospirillum brasilense strains Ab‐V5 and Ab‐V6, and SMMs extracted from B. diazoefficiens strain USDA 110 and Rhizobium tropici strain CIAT 889. Root systems were evaluated by direct (optical reading) and indirect (rubidium nitrate application, 85RbNO3) methods. Increases of up to 1.6% in root diameter (0.01‐ to 0.5‐mm class), 28.5% in length, 19.7% in root volume, 17.8% in root surface area, 29% in the number of nodules, 27.2% in nodule dry weight, 13.5% in root dry weight, and 3.8% in shoot dry weight. Greater exploration and activity within and between rows following inoculation at up to 40 and 10 cm in depth, respectively, were observed in plants co‐inoculated with the standard inoculation (only Bradyrhizobium spp.) + SMMs + A. brasilense, resulting in a yield increase of 485 kg ha−1. The results emphasize the biotechnological potential of using secondary metabolites of rhizobia with inoculants containing rhizobia and PGPR to improve the growth and soybean yield in tropical conditions.

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%.

No abstract