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Potassium (K)-based fertilizers are highly demanded in crop systems, as they are one of the elements most required by plants. Due to the high rates of K-fertilizers applied consecutively in agriculture and the doubts generated as to their permanence in soil and possible negative effects in a subsequent crop, there is a need for long-term studies that evaluate the residual effect of applications of these fertilizers on nutritional status and yield crops that make up the crop system. This study aimed to verify the effect of K-fertilizer doses applied in topdressing in maize on crop nutrition and yield, as well as soybean in succession. Nine doses of K2O (0, 15, 30, 45, 60, 75, 90, 120 and 150 kg ha−1) were applied to maize. The nutritional status and yield components were evaluated. Our results reveal the beneficial effect of applications, between 70 and 80 kg K2O ha−1 on maize nutrition and yield, as well as on soybean in succession. Consecutive K2O application in doses over 90 kg ha−1, strongly reduce the levels of leaf Ca and Mg in maize and soybean leaves and their respective grain yields. [ABSTRACT FROM AUTHOR]

Dunite [(MgFe)2SiO4] is an igneous rock that remineralizes and corrects soil acidity as well as providing magnesium (Mg2+) and silicon (Si4+) to several crops of agricultural interest. However, few studies have verified its solubility in tropical soils, which is important for its use in different tropical conditions. In a greenhouse incubation experiment, this study verified the solubilization kinetics of dunite in clayey, medium texture, and sandy soils. The soil samples were dried and sieved (50 mesh), placed in plastic cups (300 g), and incubated for six months (at 60%–80% of the moisture retention capacity). Samples for pH (CaCl2 extractor), Mg2+ (resin extractor), and Si4+ (CaCl2 extractor) analysis were taken at 10, 20, 30, 40, 50, 60, 70, 85, 100, 115, 130, 150, and 180 days after incubation. The application of dunite led to an increase in Mg2+ and Si4+ contents and an acidity correction in the three studied soils. Its controlled release presents method for increasing the efficiency of magnesium fertilization. It allows for fewer losses due to Mg2+ leaching, as the dissolution kinetics are slower than soluble sources and have a residual effect for subsequent crops. [ABSTRACT FROM AUTHOR]

Thermomagnesium (TM) or magnesium (Mg) silicate (MgSiO3) is a byproduct of the nickel (Ni) industry. As a fertilizer, TM elevates the pH of acidic soils as well as provides Mg and silicon (Si) to plants. This novel practice can be a pivotal sustainable strategy to enhance soybean [Glycine max (L.) Merrill] development, particularly in tropical environments. Therefore, the present study aimed to evaluate the effects of TM application on the chemical properties of soil; Mg and Si contents in soil and plants; contents of reducing sugars, sucrose, and starch in leaves; and yield of soybean. The experiment was performed under controlled conditions in a greenhouse during the 2016–2017 cropping season. Two soil types (clayey and sandy) and five TM rates (0, 55, 273, 709, and 2,018 mg kg−1 of TM, and 0, 293, 410, 645, and 1,260 mg kg−1 of TM, respectively) with four replicates were used. In both soil types, pH as well as Mg and Si contents increased with increasing TM rates. Similarly, leaf contents of Mg, Si, reducing sugars, and sucrose as well as yield of soybean increased with increasing TM rates. Conversely, leaf starch content decreased with increasing TM rates. Therefore, TM positively affects whole-plant carbohydrate partitioning, thereby improving soybean development, grain filling, and yield. [ABSTRACT FROM AUTHOR]

Molybdenum (Mo) is a key element in the N fixing and assimilation processes in leguminous plants. This study aimed to evaluate the effects of Mo fertilization on the yield and seed vigor of the common bean. Molybdenum was applied at six rates (0, 20, 40, 80, 120 and 160 g ha−1) in field trials over 2 consecutive years (2015 and 2016). Foliar applications were performed during the phenological stages V4 (4th trifoliolate leaf unfolded) and R1 (early flowering). The SPAD index, height of first pod insertion, number of pods per plant, number of seeds per pod, weight of 100 seeds, yield and seed vigor were determined. Molybdenum affected the production of reproductive organs only in the second agricultural year. Application of Mo at T-V4 resulted in an increase in the number of pods per plant (11%), and at 120 g ha−1, there was an increase (41%) in the number of seeds per pod, but this did not result in a yield seed increase. Molybdenum applied at the T-V4 phase reduced electrical conductivity in the first year of the experiment at rates of 40 g ha−1 (17%) and 160 g ha−1 (13%). In the second agricultural year, Mo applied at the T-R1 phase reduced in 44% the electrical conductivity, as well as the application of 20 g ha−1 also at the T-R1 phase increased seed germination (28%), seedling length (8%), and length of the primary root (10%). Different responses to the Mo application time and dose between the experimental years suggest that common bean plants recycle Mo. Molybdenum applied in the first agricultural year may have satisfied the initial Mo demand of the common beans in the second year of crop due it's low Mo requirement. This study show that foliar Mo application is an important strategy to achieve sustainable production of higher quality seeds of common bean. [ABSTRACT FROM AUTHOR]

Thermomagnesium (TM) or magnesium silicate (MgSiO3), is originally from the nickel (Ni) industry, and is a by-product that provides magnesium (Mg) and silicon (Si) to plants and corrects soil acidity. Some studies verify its solubility in tropical soils. This study evaluated the application of TM in two particle sizes (20 and 100 mesh), in sandy and medium-texture soils (Typical Oxisol), and a clayey texture soil (Typical Ultisol), in a six-month incubation experiment in a greenhouse. The soil samples were dried and sieved, placed in plastic pots, and incubated from 60 to 80% of the moisture retention capacity. Samples for pH analysis (CaCl2 extraction), Mg2+ (resin extraction) and Si4+ (CaCl2 extraction) were taken at 10, 20, 30, 40, 50, 60, 70, 85, 100, 115, 130, 150, and 180 days of TM incubation in the soils. The application of 100 mesh TM was superior owing to its greater contact surface, which increased the soil content of Mg and Si, and corrected the acidity in the three soils that were studied. The controlled release of TM (100 mesh) increased Mg fertilization efficiency, since less Mg2+ is lost by leaching, owing to the slower dissolution kinetics than soluble sources. The TM adjusts to the demand of the plants and has a residual effect for subsequent crop seasons. [ABSTRACT FROM AUTHOR]

Using sustainable management to maximize crop yield without increasing production costs is one of the great challenges of modern agriculture. This study aimed to evaluate the effect of nitrogen (N) supply management, associating inoculation with Rhizobium tropici, co-inoculation schemes with Azospirillum brasilense and mineral top-dressing fertilization, on the agronomic and qualitative performance of early-cycle common bean cultivars. The experiment was installed in a randomized block design, in a 2 x 12 factorial scheme (2 cultivars and 12 N supply management), with four repetitions. The N supply management consisted of the association of mineral fertilization with N (45 and 90 kg ha−1 of N in top-dressing), inoculation of seeds with Rhizobium tropici and co-inoculation of seeds and leaves with Azospirillum brasilense. The agronomic and qualitative performance of common bean was affected by the nitrogen supply management and by the cultivars, and the response was independent of the interaction between cultivars and N supply management. Except for plant dry mass, all variables analyzed showed maximum response in the treatment of seed inoculation with Rhizobium tropici, leaf-spray of Azospirillum brasilense and mineral top-dressing fertilization with 90 kg ha−1 of N, which led to a 27% increase in yield compared to the control. The cultivar IAC Imperador has a superior agronomic performance (grain yield = 2,840 kg ha−1) compared to IPR Curió (2,484 kg ha−1). The results demonstrated the feasibility of using co-inoculation with Azospirillum brasilense as a tool to increase yield, grain quality and sustainability in common bean production systems. [ABSTRACT FROM AUTHOR]

This study aimed to assess the physiological and biochemical responses of cotton plants to manganese (Mn2+) nutrition. Four cotton genotypes (G1 – TMG 47; G2 – FM 975 WS; G3 – TMG 11 WS and G4 – IMA 8405 GLT) were grown in nutrient solution under two Mn2+ concentrations (2 and 200 µmol L−1) for 10 days. No visible symptoms of Mn2+ toxicity were observed in the genotypes tested. All genotypes showed a marked increase in leaf chlorophylls, pheophytins, carotenoids, sucrose and total sugars concentration in response to high Mn2+ in a nutrient solution. However, the net photosynthetic rate, stomatal conductance, internal carbon dioxide concentration and transpiration decreased in genotypes G1 and G2 growing under 200 µmol L−1. Antioxidant enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) activities increased in genotypes G1, G3 and G4. Cotton genotypes showed an increased leaf antioxidant and sugar metabolism as a possible strategy to mitigate oxidative stress. The decrease in the net photosynthetic rate and stomatal conductance; the increased antioxidant enzymes activities (SOD, APX and GR); and the increase in leaf sucrose and total sugar concentration were the main physiological and biochemical responses in cotton plants to Mn2+ stress. [ABSTRACT FROM AUTHOR]