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Soybean [Glycine max (L.) Merr.] is highly efficient in the biological N2 fixation (BNF) process through the association of bacteria of the genus Bradyrhizobium in the root nodules of the plants. However, there are still doubts about the need to complement soybean N demand through N fertilization in high‐yield environments. In addition, the real impact of co‐inoculation of soybean with Azospirillum brasilense and Bradyrhizobium spp. is not yet clear in such environments. A field experiment was conducted from 2012 to 2021 with six soybean cropping seasons in a crop rotation scheme with black oat (Avena strigosa Schreb), maize (Zea mays L.), and wheat (Triticum aestivum L.) under no‐till (NT) in Southern Brazil. Soybean seeds were co‐inoculated with A. brasilense (strains Ab‐V5 and Ab‐V6) shortly after inoculation with Bradyrhizobium japonicum, and different levels of N fertilization were used in top dressing at the start of pod formation (R3). Soybean nutritional status and grain yield were not benefited by co‐inoculation with A. brasilense. Since the increased inoculum rate of A. brasilense co‐inoculated with rhizobia in soybean compromised both N nutrition and grain yield, this practice should not be encouraged. There was no need to complement soybean N demand through N fertilization during the reproductive stage. Soybean achieved grain yields of 5.0–5.7 Mg ha−1 and, even so, there was no need to complement N demand through N fertilization. The results suggest that soybean N demand in a high‐yielding environment under NT could be satisfied exclusively through the optimization of BNF. Core Ideas: Benefits of co‐inoculation of soybean with Azospirillum brasilense are unclear.Late N fertilization in soybean is an unnecessary practice.Co‐inoculation and N fertilization did not improve soybean nutrition and yield.N fertilization for no‐till soybean production should not be encouraged.Increased inoculum rate of A. brasilense in soybean should not be encouraged. [ABSTRACT FROM AUTHOR]

The benefits of applying phosphogypsum to the soil are widely known. However, the effect of phosphogypsum on phosphate fertilization efficiency is still unclear. A long-term field experiment was performed on an Oxisol in Parana State, Brazil to evaluate the effects of triple superphosphate (TSP) and phosphogypsum application rates on nutrition and grain yield of soybean, wheat, and black oat under no-till. Applying TSP in the sowing furrow of soybean and wheat increased soybean yield by 14 to 24%, wheat yield by 57%, and black oat yield by 78%. Soybean yields varied in different cropping seasons in response to phosphogypsum application (with no response to increases of up to 15% in yield), while phosphogypsum increased wheat yield by 23% and black oat yield by 59%. The water balance during crop flowering possibly interfered on crop yield response to phosphogypsum. The use of phosphogypsum increased agronomic P-use efficiency by 20%, regardless of the TSP-P application rates. Changes in P-leaf concentration caused by TSP fertilization and phosphogypsum use had a positive impact on crop grain yield. Our results reveal that the continued use of phosphogypsum to alleviate subsoil acidity could increase the phosphate fertilization efficiency and improve crop yield performance under drought stress. [ABSTRACT FROM AUTHOR]

Root growth and crop yield can be affected by chemical modifications of the soil profile owing to lime and gypsum applications. A field trial was carried out on a dystrophic Clayey Rhodic Hapludox at Ponta Grossa, PR, Brazil, aiming to evaluate lime (without or with incorporation into the soil) and gypsum effects on root growth, mineral nutrition and grain yield of wheat (cv. OR 1). A randomized complete block design was used, with three replications, in a split-plot experiment. Treatments with dolomitic limestone (without lime and 4.5 t ha-1 of lime applied on the surface, in total rate and 1/3 of the requirement per year during 3 years, or incorporated into the soil) were applied in July 1998 (main plots) and the rates of gypsum (0, 3, 6 and 9 t ha-1) in October 1998 (subplots). Wheat was evaluated in the 2000 winter season. In conditions of water deficit absence, there was no limitation in root growth in depth, for exchangeable Ca of 6 mmol c dm-3. Lime incorporation of lime increased the Mg concentration in the leaves, but wheat yield was not influenced by the correction of soil acidity through liming treatments. Gypsum increased the concentrations of Ca and S in wheat leaves, with significant effects on grain yield. The critical level of S-SO4(2-) in the 0-20 cm soil layer, extracted by ammonium acetate 0.5 mol L-1 in acetic acid 0.25 mol L-1, was 25.8 mg dm-3.

High-intensity crop-production seeking for higher grain yields increases nutrient demand by plants. A field experiment was performed in Parana State, Brazil, on a clayey Haplic Cambisol to evaluate the effects of phosphogypsum and nitrogen (N) amendments on a wheat–soybean rotation. Phosphogypsum was surface-applied to plots at 0, 2, 4, and 6 Mg ha−1 before wheat sowing and two rates of urea at 40 and 80 kg N ha−1 were applied to subplots in top dressing at tillering of wheat. Phosphogypsum improved the yield performance of wheat–soybean rotation. Wheat grain yield increased by 20% due to phosphogypsum application only when a higher rate of urea at 80 kg N ha−1 was applied in top dressing, indicating an influence of the interaction between N and sulfur (S). Soybean grain yield increased by 16% with phosphogypsum application, regardless of the urea-N rates to the previous wheat crop. Higher grain yields of wheat and soybean were related to higher levels of Ca2+ and S in the soil profile (0–0.40 m). Although there was a slight involvement of phosphogypsum in reducing aluminum Al3+ toxicity in the subsoil due to a reduction in Al3+ saturation caused by increased Ca2+ concentration, the improvements imparted by the use of phosphogypsum resulted mainly from increased S concentration. The results showed that the critical levels of SO4–S by 0.01 mol L−1 Ca(H2PO4)2 were 14 and 27 mg dm−3 at 0–0.20 m and 0–0.40 m depths, respectively, for the wheat–soybean cropping system. [ABSTRACT FROM AUTHOR]

Long-term surface application of lime (L) and/or phosphogypsum (PG) in no-till (NT) systems can improve plant growth and physiological and biochemical processes. Although numerous studies have examined the effects of L on biomass and plant growth, comprehensive evaluations of the effects of this practice on net CO2 assimilation, antioxidant enzyme activities and sucrose synthesis are lacking. Accordingly, this study examined the effects of long-term surface applications of L and PG on soil fertility and the resulting impacts on root growth, plant nutrition, photosynthesis, carbon and antioxidant metabolism, and grain yield (GY) of maize established in a dry winter region. At the study site, the last soil amendment occurred in 2016, with the following four treatments: control (no soil amendments), L (13 Mg ha–1), PG (10 Mg ha–1), and L and PG combined (LPG). The long-term effects of surface liming included reduced soil acidity and increased the availability of P, Ca2+, and Mg2+ throughout the soil profile. Combining L with PG strengthened these effects and also increased SO42–-S. Amendment with LPG increased root development at greater depths and improved maize plant nutrition. These combined effects increased the concentrations of photosynthetic pigments and gas exchange even under low water availability. Furthermore, the activities of Rubisco, sucrose synthase and antioxidative enzymes were improved, thereby reducing oxidative stress. These improvements in the physiological performance of maize plants led to higher GY. Overall, the findings support combining soil amendments as an important strategy to increase soil fertility and ensure crop yield in regions where periods of drought occur during the cultivation cycle. Schematic summary of the main effects of lime and phosphogypsum on soil fertility, root growth and maize physiology. [ABSTRACT FROM AUTHOR]

Cereal crops have a high N requirement in a high‐yield environment. However, N use efficiency is still low in agricultural production systems and little is known about the effects of inoculation with Azospirillum brasilense in a high‐yield environment. A field experiment was conducted from 2012 to 2018 with a maize (Zea mays L.)–wheat (Triticum aestivum L.) rotation under a continuous no‐till in southern Brazil. Seeds were inoculated with A. brasilense (strains Ab‐V5 and Ab‐V6) and different levels of N fertilization were used in top dressing. Seed inoculation provided slight changes in N, P, and K concentrations in leaves and grains of maize and wheat. Increasing N input increased the leaf and grain N concentration and the maize and wheat grain yields. Seed inoculation caused varied responses on cereals in different cropping seasons. Wheat was more affected by inoculation in response to N application than maize. Rainfall distribution during the growing seasons possibly interfered on crop responses with inoculation between years and N fertilization levels. Under a similar N input, inoculation resulted in an average increase of 454 kg ha−1 yr−1 of maize and 242 kg ha−1 yr−1 of wheat by applying a higher N rate to the maize and a lower N rate to the wheat. An additional gain of US$409.72 ha−1 (2012–2018) was also achieved using this strategy. Although the possibility of inoculation causing economy with N fertilization in wheat was evident, for maize in rotation with wheat, A. brasilense inoculation was apparently more viable under higher N fertilizer input. [ABSTRACT FROM AUTHOR]

Our study examined whether the nutrient content analysis of soybean seed could be used to assess the plant nutritional status, generating results as or more accurate than those obtained by leaf analysis. We hypothesized that soybean nutritional assessment could be carried out using seeds as a reference. Nutritional diagnosis in soybean leaves and seeds was assessed using the Mathematical Chance (MCh), Diagnosis and Recommendation Integrated System (DRIS), and Compositional Nutrient Diagnosis (CND) methods. Results showed that optimal nutrient levels in soybean leaves and seeds estimated by DRIS and CND were equal or close to the average content in the reference population, while slightly different values were obtained by MCh method. Nutrient average contents were larger for soybean seeds than for leaves for nitrogen, phosphorus, sulfur, and zinc; and lower for potassium, calcium, magnesium, boron, copper, iron, and manganese. The ranges of optimum levels obtained for seed nutrient content showed normality in results for the three studied methods (MCh, DRIS, and CND). This indicates that using seeds as a diagnostic tissue for assessing soybean nutritional status is promising. Optimal nutrients levels in soybean seeds estimated mainly by the CND and DRIS methods could help to monitor soybean nutritional status. [ABSTRACT FROM AUTHOR]

This study aimed to develop a novel regression model for prescription of required nitrogen (N) for maize by combining spectral reflectance data from GreenSeeker sensor and agronomic efficiency. For this end, two field trials at two sites were carried out with maize (Zea mays L.) on Oxisols under no-till systems in Southern Brazil. For both experiments, a randomized complete block design, with three replications in a split-plot arrangement, was used. The main plots consisted of four urea-N rates at sowing (0, 20, 40, and 60 kg N ha−1) and subplots included four urea-N rates in top dressing (0, 80, 160, and 240 kg N ha−1). Based on the results, a novel model for prescription of N rate in top dressing for maize was defined. The increases in maize yields with the N rates estimated by the model (16% to 39%) were similar to that obtained with the N rates used for maximum economic yield (15% to 42%). The estimated N rate by the model provided an economic return 36.5% and 7.0% higher than the N rate for maximum yield, and only 6.6% and 2.0% lower than the N rate for maximum economic yield, at sites 1 and 2, respectively. Thus, the economic return obtained using the model was closer to that reached with the N rate for maximum economic yield than that for maximum yield. Therefore, the developed model, combining spectral reflectance and agronomic efficiency, exhibited great potential to improve the maize N fertilization efficiency. [ABSTRACT FROM AUTHOR]

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Copyright of Acta Scientiarum: Technology is the property of Universidade Estadual de Maringa and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista Ciência Agronômica is the property of Revista Ciencia Agronomica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The complex dynamics of the sulphur (S) cycle has prompted several questions concerning its bioavailability and evaluation by different extraction methods, and few studies under field conditions have been performed to elucidate available S on Brazilian soils under no-till (NT) cropping systems. A field experiment examined the effects of phosphogypsum (PG) applications on nutrient uptake and availability of S to maize and wheat crops under an NT system aiming to establish critic levels of S on an Oxisol (clay, kaolinitic, Rhodic Hapludox) in Parana state, Brazil. PG at the rates of 0, 3, 6 and 9 t ha−1 was applied on the surface of the plots in 1998 upon conversion from pasture to an NT cropping system, and in 2004 subplots received either 0 or 6 t ha−1 of PG on the surface. Effects of PG applications on nutrient uptake and available soil SO4-S to the maize and wheat crops were evaluated in 2004–2005. Increasing the surface-applied PG rate in 1998 increased Mg uptake by maize, and N, K, Ca and Mg uptake by wheat plants. Reapplication of PG in 2004 increased the uptake of N and P by maize, and the uptake of N, K, Ca and Mg by wheat plants. The PG rates surface-applied in 1998 have resulted in a long-term residual effect on soil by increasing SO4-S in surface and subsoil layers 6.5 and 7.5 years after application, affecting aboveground biomass, S uptake and S content in the leaves of the wheat crop. The reapplication of PG in 2004 increased maize S uptake, S content in leaves and grains and S exported by maize harvest, and increased wheat aboveground biomass, S uptake and S content in leaves. These effects were due to increasing available soil SO4-S from different depths extracted by 0.5 M ammonium acetate (NH4OAc) along with 0.25 M acetic acid (HOAc) and 0.01 M calcium phosphate (Ca(H2PO4)2). Both extractants were very similar in their ability to assess available soil S in these crops, and the 0–0.20-m layer is shown to be adequate for evaluating the concentration of available SO4-S in maize and wheat cultivated under NT. [ABSTRACT FROM AUTHOR]

In a no-till system (NTS) on naturally acidic soils, surface liming is essential to neutralize soil acidity and increases crop productivity. As a result, the soil organic matter (SOM) pools of the soil surface layers may change, reflecting increased C inputs by crop residues. The objective of this study was to quantify changes in SOM pools and the rate of C sequestration that occur in response to surface liming in a long-term NTS experiment. The experiment was conducted in an Oxisol in southern Brazil. The treatments consisted of the application of 0 or 6 Mg ha-1 of dolomitic lime on the soil surface in 1993 and a reapplication of 0 or 3 Mg ha-1 of dolomitic lime in 2000 to plots with or without the previous lime application. Liming caused total organic C (TOC) accumulation, especially in the 0- to 2.5-cm layer. The amount of TOC stored in the 20-cm layer was 49.9, 52.9, 52.7, and 57.5 Mg ha-1 in the control, 6 + 0, 0 + 3, and 6 + 3 Mg ha-1 treatments, respectively. The levels of particulate organic C (POC) and mineral-associated organic C (MAOC) in the SOM were also enhanced by liming. The increase in POC was directly related (R² = 0.99, P = 0.002) to the accumulation of C from crop residues, which was greater in the plots receiving lime treatment. There were positive correlations between TOC and C extractable with hot water, total polysaccharides, and labile polysaccharides. The correlation analysis also demonstrated that TOC was more tightly correlated with POC than with MAOC, indicating a greater influence of the labile fraction on the increase in TOC with surface liming. [ABSTRACT FROM AUTHOR]

Abstract: Crop residues that are left on the soil surface to serve as mulch can diminish the soybean response to surface application of lime under no-till management by ameliorating soil chemical and physical attributes and the plant nutrition. A field experiment was performed in the period from 2000 through 2003 in Parana State, Brazil, on a clayey-sandy Rhodic Hapludox. Soil chemical attributes and soybean [Glycine max (L.) Merrill] nutrition, grain yield, and quality were evaluated after surface application of lime and covering with crop residues of black oat (Avena strigosa Schreb) and corn (Zea mays L.) under a no-till system. Dolomitic lime was surface applied at the rates of 0, 2.5, 5.0, and 7.5 t ha-1 on the main plots, and three treatments with vegetable covering were applied on the subplots: (i) without covering, (ii) with covering of corn straw, and (iii) with covering of corn straw and black oat residue (oat-corn-oat). After 30 months, surface-applied lime increased soil pH and the exchangeable calcium (Ca2+) and magnesium (Mg2+) levels down to a 10-cm depth, independent of the vegetable covering treatments. The black oat and corn residues on the soil surface increased the soil exchangeable K+ level at the 5- to 10-cm depth. Liming increased leaf potassium (K) content and phosphorus (P) content in the soybean grain and reduced leaf zinc (Zn) content and manganese (Mn) content in the soybean leaf and grain. There was no effect of liming on soybean grain, oil, or protein yields, independent of the vegetable residues kept on the soil surface. The treatment with black oat covering and corn straw increased leaf N content, P content in the leaf and grain, and the contents of K, Mg, copper (Cu), and Zn in the soybean grain. It also increased soybean grain and protein yields. The corn straw left at the surface after harvesting was very important to the performance of the no-till soybean. [ABSTRACT FROM AUTHOR]

Field experiments have been used to explain how soil organic carbon (SOC) dynamics is affected by lime and gypsum applications, however, how SOC storage occurs is still debatable. We hypothesized that although many studies conclude that Ca-based soil amendments such as lime and gypsum may lead to SOC depletion due to the enhancement of microbial activity, the same does not occur under conservation agriculture conditions. Thus, the objective of this study was to elucidate the effects of lime and gypsum applications on soil microbial activity and SOC stocks in a no-till field and in a laboratory incubation study simulating no-till conditions. The field experiment was established in 1998 in a clayey Oxisol in southern Brazil following a completely randomized blocks design with a split-plot arrangement and three replications. Lime and gypsum were surface applied in 1998 and reapplied in 2013. Undisturbed soil samples were collected before the treatments reapplications, and one year after. The incubation experiment was carried out during 16 months using these samples adding crop residues on the soil surface to simulate no-till field conditions. Lime and gypsum applications significantly increased the labile SOC stocks, microbial activity and soil fertility attributes in both field and laboratory experiments. Although the microbial activity was increased, no depletion of SOC stocks was observed in both experiments. Positive correlations were observed between microbial activity increase and SOC gains. Labile SOC and Ca 2 + content increase leads to forming complex with mineral soil fractions. Gypsum applications performed a higher influence on labile SOC pools in the field than in the laboratory experiment, which may be related to the presence of active root system in the soil profile. We conclude that incubation experiments using lime and gypsum in undisturbed samples confirm that soil microbial activity increase does not deplete SOC stocks under conservation agriculture. [ABSTRACT FROM AUTHOR]

The application of lime and gypsum has been recognized as an important strategy for correcting soil acidity and for improving soil fertility, soil aggregation, and agronomic productivity in highly weathered soils. We hypothesized that the combined application of lime and gypsum would create favorable conditions for biological activity and result in increased SOC storage and agronomic productivity. Thus, the aim of this study was to evaluate the long-term ( i.e. , 15 years) impact of lime and gypsum application on the biological activity, SOC stocks, and agronomic productivity of plots under no-till soil management. The experiment was established in 1998 at a site with clayey Oxisol in southern Brazil, and was designed with a split-plot arrangement, completely randomized blocks, and three replicates. The main plot was subject to three lime treatments: (i) control (no lime); (ii) incorporated lime (IL):incorporation of 4.5 Mg lime ha −1 to a depth of 0–20 cm by; and (iii) surface lime (SL): surface application of 4.5 Mg lime ha −1 , which was equally divided among three annual applications during the first three years of the experiment. The subplots were comprised by surface applications of gypsum at 0, 3, 6, or 9 Mg ha −1 . Soil samples were collected in 1998, before of the experiment, and in October 2013, in order to evaluate soil enzyme activities, SOC pool stocks, crop productivity, C-biomass input, and soil fertility attributes. Both forms of lime application significant improved the stocks of several SOC pools, crop productivity, biomass-C input rates, soil fertility attributes, and enzyme activity. The SOC stocks were positively correlated with Ca 2+ content and biomass-C input, demonstrating the potential of calcium to improve C accumulation. Enzyme activities were significantly affected by both soil fertility and SOC pools, with increases in hot water extractable organic C yielding the greatest increases in enzyme activity. In addition, we also found that gypsum application significantly increased the stocks of labile SOC pools and arylsulfatase activity. However, effects of gypsum application were less apparent than those of lime application and the combination of surface lime (4.5 Mg ha −1 ) and gypsum (9 Mg ha −1 ) application yielded the greatest long-term increase in the stock of total organic C stock. Thus, the results of the present study suggest that lime and gypsum application, along with no-till management and biomass-C input, constitutes an efficient strategy for improving the biological activity, C stocks, and productivity of agricultural soils. [ABSTRACT FROM AUTHOR]

Although Azospirillum brasilense is used in many inoculant formulations, information of its prevalence under field conditions is still scarce. In this work, we inoculated A. brasilense AbV5/AbV6 (2 × 108 CFU ml−1) on maize seeds and then evaluated its colonization profile throughout seventy-five days after seeding (DAS) in a field assay. The abundance of total bacteria and A. brasilense on the seed, root and soil rhizosphere were determined by qPCR using 16S rRNA and species-specific primers, respectively. A. brasilense was detected in soil at a concentration of 105 CFU g−1 of soil only until radicle emergency. From the fifth day onwards, it was detected at the roots in a concentration of 103 to 105 CFU g−1 of fresh root. Our results provide a sensitive approach to monitor A. brasilense in a field trial and reveal new information on the ecology of maize and A. brasilense association. Unlabelled Image • brasilense was tracked by qPCR throughout seventy-five days under field conditions. • Right after radicle emergence, A. brasilense was detected only at maize roots. • brasilense at 105 CFU g−1 of fresh root increased maize yield. • An accurate approach for tracking and quantifying A. brasilense in the field was developed. [ABSTRACT FROM AUTHOR]