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ABSTRACT: It remains unclear whether temperature and precipitation exert independent control on tropical vegetation and soil C pools. Likewise, it is unknown whether the feedbacks of tropical C pools to climate constraints vary with nutrient availability. These aspects are critical to improving our ability to predict the response of tropical C pools to climate dynamics. This review aimed to assess climate data and the spatial distribution of vegetation and soil C pools across the Brazilian territory to investigate i) whether mean annual precipitation (MAP) and temperature (MAT) exert independent effects on tropical C pools; ii) whether vegetation and soil C pools exhibit hierarchical feedbacks to climate; and iii) how these feedbacks reflect soil nutrient availability. To account for MAP and MAT effects on tropical C cycling, we calculated Ecosystem Effective Moisture (EEM), i.e., the difference between MAP and potential evapotranspiration. We gathered substantial evidence suggesting that under high MAT and MAP controlling EEM, plants exchange more C for water and resorb more nutrients (especially P), which limitations in plant litter reduce microbial-derived C inputs into soil organic matter. Frequent soil saturation under high EEM favors denitrification rates (“open” N cycle), allowing continuous mineralization of litter and shallow soil C pools to release nutrients, sustaining high plant C pools. With decreasing MAP levels, ecosystem C pools depend on MAT controlling evapotranspiration and EEM. Accordingly, decreasing MAP under high MAT reduces EEM, with vegetation and soil C pools co-limited by low net primary productivity (NPP), frequent fire and/or nutrient losses. Otherwise, decreasing MAP and coupled to cool temperatures allow EEM to remain positive, forcing plants to increase deep-rooting and/or shed their leaves, which nutrients are immobilized with microbial-derived C into mineral-organic associations, favoring high soil C pools. Combined, the evidence gathered suggests that the sensitivity of tropical ecosystems to global increases in temperature should not be overlooked, especially if coupled to reductions in precipitation. Overall, the horizontal distribution of vegetation and soil C pools is best described by EEM rather than temperature or precipitation alone, whereas the vertical partition of C in plant-soil systems reflects biotic responses to climate-nutrient constraints.

ABSTRACT Leaf-cutting ants are the most important herbivore in the neotropics, represent active agents of pedobioturbation, and are regarded as ecosystem engineers. These ants have a wide variety of ecological functions, such as pollination, seed dispersal, and tree-growing control. Despite this importance, little is known on their distribution in relation to possible soil and environmental conditions that affect Atta ants occurrence. This study aimed to spatialize the main occurrences of Atta species in the Brazilian territory and evaluate the main environmental conditions driving ants species in the Brazilian tropical landscapes, at a preliminary basis. We compiled data of occurrence for 12 Atta species from Global Biodiversity Information Facility (GBIF) databases, and scientific literature (up to 2019) for each Atta species. To each point, we obtained the respective geoenvironmental data as soil properties, biome, geology, vegetation land use, and climate variables. From these data, possible zonalities of occurrence of 9/10 Atta species were discussed. We applied the principal components analysis (PCA) and Canonical Correspondence Analysis (CCA) to identify the environmental gradient and investigate the possible interplay between variables and species. Soil, vegetation, and land use attributes are the main drivers on the distribution of Atta at local scale where their evolutionary physiological and foraging adaptations allow them to nest and maintain the fungi culture. At broader scales, climatic attributes are key drivers of Atta distribution across Brazil, and also influence pedogenic processes. Our study demonstrates that species of Atta ants are not randomly dispersed in Brazil and are strongly associated with complex and diverse Brazilian landscapes. We remark that further studies on the distribution of leaf-cutting ants of the Atta genus in Brazil, as well as their evolutionary phylogenetics, are needed, based on larger database.

ABSTRACT Extracellular soil enzymes are fundamental for the functioning of ecosystems. Several processes in the soil depend on the activity of these enzymes, including plant decomposition, soil organic matter formation/mineralization, and nutrient cycling. Moreover, extracellular enzyme activity occurs in the soil and is therefore influenced by environmental factors. Due to the high sensitivity to these factors, extracellular enzymes are used for monitoring soil quality. This review aimed to present the main contributions of soil enzymes to agriculture, emphasizing the dynamics of elements in the soil and the environmental factors that modulate enzyme activity. With this knowledge, the relationship of extracellular enzymes to soil quality is demonstrated and their use as a tool for soil monitoring. Finally, the evolution of research on soil enzymes in Brazil is presented, and the perspectives of basic and applied studies necessary to expand the knowledge and use of enzymes in soil management are pointed out. Soil enzymes play a key role in numerous soil processes, thereby making them useful indicators of productive capacity and soil quality. Research on enzymes in soil has developed significantly in the last two decades, which has made it possible for farmers to analyze and interpret enzyme activity in the soil in the laboratory.

ABSTRACT: Litter decomposition dynamics and nutrient release are also dependent on their biochemical composition, and such information is important for adequate nutritional management but is still incipient for plants like teak. This study aimed to evaluate the decomposition dynamics, nutrient release, and biochemical composition of clonal teak litter. The study was conducted in areas of clonal teak stands, in São José do Rio Claro, Mato Grosso, Brazil. Litter collectors were arranged in the area to collect material along the entire dry period. Subsequently, this litter was placed in litter bags, which were distributed in the area. The litter bags were collected every month, for 0.91 years, to determine the dry matter and mineral nutrient contents, in order to estimate the decomposition and nutrient release. Litter biochemical composition was determined at the times of 0, 0.25, 0.58, 0.75, and 0.91 years. Teak litter, essentially leaves, had a half-life time (t1/2) of dry matter and C of 0.74 years, due to the high content of insoluble lignin, which corresponds to 2.28 Mg ha-1 of dry matter and 1.2 Mg ha-1 of C. The t1/2 values of N and P release (1.20 and 1.01 years) were higher than those of K, Ca, and Mg (0.08, 0.47, and 0.66 years, respectively). Hence, the nutrient release rate of the litter followed the descending order: K > Ca > Mg > P > N. The litter biochemical composition at the end of the experimental period showed reductions of 18.7 % in polysaccharides and holocellulose, 56 % in polyphenols, 56.3 % in tannins, 22.2 % in extractives, and 28.5 % in soluble lignin; and increases of 25.6 % in insoluble lignin and 22.6 % in total lignin. These data are useful for the balance of carbon and mineral nutrients and to support fertilization management in teak plantations in low-fertility soils.

ABSTRACT: Accidents related to the rupture of iron ore tailings dams have dramatically impacted on the Brazilian natural ecosystem. So, the development of strategies to recover soil organic matter levels and build-up Technosols are required. This study aimed to evaluate the effect of N-mineral and -organic fertilization and the rhizospheric effect on soil organic matter mineralization from Technosols built under iron ore tailings. The experiment was carried out in a greenhouse; we used a factorial scheme 2 × 2 × 3: without and with the plant Crotalaria juncea ; without and with mineral fertilization; and three different organic fertilization (without organic fertilization, sewage sludge, and household waste composting), with four randomized blocks. The experimental units were PVC columns installed with a top layer of iron ore tailing from a dam, where gases were sampled to determine the CO2-C, CH4-C concentrations, and CO2-δ13C. The organic fertilization promoted a positive priming effect of 184 %. However, with mineral fertilization, no effect was observed in soil derived-CO2-C accumulated and priming effect. Similarly to non-planted soil, the planted soils with mineral and organic fertilization promoted a steady reduction in soil derived-CO2-C accumulated and rhizosphere priming effect. The soil with mineral fertilization improved in 5.52 and 0.45 g per column the shoot and root dry matter of Crotalaria when compared to the soil without mineral fertilization. In summary, the organic fertilization in Technosols built over iron ore tailings dams during revegetation was not enough to ensure the plant development and preservation of soil organic matter. However, the combination of mineral and organic fertilization promoted negative rhizosphere priming effect and a significant increase in plant biomass.

ABSTRACT Tissue analysis results are interpreted by comparing them with nutrient standards; however, using universal standards may lead to a misleading nutritional diagnosis. This study aimed to evaluate the degree of universality of Kenworthy and DRIS norms for irrigated ‘Prata-Anã’ (AAB) and ‘Grande Naine’ (AAA) banana plants grown in two environments. The study was carried out using a database containing leaf nutrient contents and yield data of two farms located in Ponto Novo, Bahia State, and Missão Velha, Ceará State, Brazil. A reference population was that with yields above the average yield plus 0.5 standard deviation. Using a reference population, the mean, standard deviation, and coefficient of variation of nutrient content and dual nutrient ratios were calculated for each site × cultivar combination. To verify the homogeneity of variance among populations, F-test was used (p≤0.05). Means were compared using t-test (p≤0.05). Differences in climate and soil at each farm explain the high frequency of significant differences found between norms for each site. Kenworthy norms established for interpreting leaf nutrient contents of P, K, Ca, Mg, S, Cu, Fe, Mn, and Zn for ‘Prata-Anã’ grown in Ceará were higher than those in Bahia, while for N and B contents, the norms were higher in Bahia. This is due to differences in soil fertility and alkalinity affecting nutrient availability as well as non-nutritional factors. Kenworthy and DRIS norms for ‘Prata-Anã’ and ‘Grande Naine’ bananas grown in Ceará have higher variability and are greater than for those grown in Bahia. Norms are less convergent for ‘Prata-Anã’ than ‘Grande Naine’. Site- and cultivar-specific norms are recommended over universal ones for assessing the nutritional status of ‘Prata-Anã’ and ‘Grande Naine’ banana plants cultivated in different environments.

ABSTRACT Soil chemical and physical analyses are the major sources of data for agriculture. However, traditional soil analyses are time-consuming, not cost-efficient, and not environmentally friendly. An alternative to traditional soil analyses is soil spectroscopy. This technique is a low-cost and quick analytical method, which can be implemented in a laboratory and/or in-situ. Nevertheless, some spectrometers are expensive and do not contemplate the entire spectrum. Despite this limitation, the main objective of the study was to create a soil spectral library of the Piauí State using only the 1000–2500 nm range. In this sense, it was evaluated and standardized the soil spectral library by accessing the combination of smoothing, standard normal variate, continuum removal, and Savitzky-Golay derivative spectral preprocessing procedures with partial least squares, random forest, and cubist machine learning algorithms. It was collected 262 geo-referenced soil samples at the layer of 0.00–0.20 m across the entire Piauí State, representing most of its soil variability. The soil properties evaluated were pH(H2O), sand, clay, and soil organic carbon (SOC) contents. This study demonstrated that the Standard Normal Variate was one of the most promising preprocessing procedures to improve model predictions for pH(H2O), sand, and clay. For SOC and pH, the best overall results were without preprocessing the soil spectra. Moreover, the cubist model was the most accurate in predicting soil properties. Finally, our study showed evidence of the potential and feasibility of using this soil spectral library to estimate soil properties such as pH(H2O), sand, clay, and SOC.

ABSTRACT The phosphorus (P) rates recommended for corrective fertilization-P of soils from southern Brazil may be insufficient to reach the critical level for optimal plant growth. This study aimed to quantify the fertilizer-P rates for total correction fertilization with varying soil buffering capacity in the states of Rio Grande do Sul (RS) and Santa Catarina (SC). Soil samples from 0.00-0.10 and 0.10-0.20 m layers were collected from 41 locations distributed in both states. Twelve P rates were applied to each soil, varying between 0 and 100 % of the maximum adsorption capacity (P-max), and incubated for 20 days. After incubation, the extractable P was determined by Mehlich-1. Based on the relationship between applied rates and extracted P, the P buffer capacity (trP_M1) of the soils was quantified, relating it to soil properties. The trP_M1 values, that is, amounts of P2O5 required to increase 1 mg dm-3 of P extracted by Mehlich-1, varied between 2.4 and 34.5 kg ha-1 of P2O5. A multiple explanatory equation for the variable P was generated, in which only P-max, clay content, and initial P availability have a significant effect. The P buffer capacity was significantly higher in the soils with the highest clay content, and there was a reduction in trP_M1 for soils with higher initial P availability. Considering 270 soil samples with low P, the P rate to reach the sufficient levels may be 2-folds higher than the values currently indicated for the RS and SC states, especially for soils with more than 40 % of clay. Phosphorus rates for corrective fertilization must be based on the soil clay content and in P initial availability. The fertilizer-P in clayey soils must be increased.

ABSTRACT An important strategy for the sustainable management of Cerrado soils is no-till (NT) systems, which may improve soil properties, particularly aggregation. Soil aggregates can be categorized according to their formation pathways into physicogenic (Phy) and biogenic (Bio). This study aimed (i) to quantify the relative proportion of physicogenic and biogenic aggregates and (ii) evaluate the levels of total organic carbon and their respective humic and physical fractions in the aggregates’ formation pathways. The following managed and unmanaged sites were evaluated: a 6-year no-till site (6NT), an 18-year no-till site (18NT), a conventional tillage site (CT), and a reference Cerrado site (RS). Retained aggregates were analyzed morphologically, separated into Phy and Bio, and quantified. Subsequently, aggregates were subjected to total organic carbon (TOC) determination, fulvic acid carbon, humic acid carbon, humin carbon, particulate organic carbon (POC), mineral-associated organic carbon, and free light fraction carbon (FLFC). The proportion of Bio aggregates increased with decreasing management intensity. When TOC and humic acid carbon levels were compared between sites, it was found that Bio aggregates from 18NT and 6NT contained higher carbon content than Bio aggregates from CT. Particulate organic carbon and FLFC differed between aggregate types, with higher POC values observed in Bio aggregates from CT and 18NT and higher FLFC values in Bio aggregates from CT, 6NT, and 18NT. The practices adopted in the conservation management system favored biogenic aggregation in the Cerrado region, which can be proven through the study of the fractions of soil organic matter contained in these aggregates. The biogenic aggregation changed the SOM dynamics. Principal component analysis showed a clear distinction between conventional and conservationist management systems.

ABSTRACT Continually rising scarcity in water and nutrient resources, especially in semi-arid agricultural systems, combined with increased frequency of extreme weather events such as drought, contribute to a growing need for resilient and regenerative agricultural ecosystems. However, evaluating a myriad of combinations of producer-led sustainable management practices in on-farm research remains challenging. Few studies have elucidated spatial variability in measured soil properties across the study area due to logistical and economic constraints. As such, this study aimed to: 1) establish soil health assessment and landscape variability data immediately after land-use change to a sustainable pasture management system, and 2) delineate relationships and predictive capability between measured soil health parameters. Soil samples were collected on May 23, 2018 in a grid pattern across two adjacent pastures on a farm in the semi-arid Southern High Plains (Texas, USA) that had recently been converted from long-term continuous cotton production to grazed pasture. Significant differences were found in soil chemical and biological properties between pastures (e.g., ~37 % reduction in microbial community size and 36 and 178 % greater electrical conductivity (EC) and Na contents, respectively, in the East pasture) that likely resulted from recent tillage and receiving irrigation compared to similar soil types and management history in the West pasture. Spatial diagrams of measured parameters revealed localization of measured properties, such as higher clay content and soil organic matter in the southeastern portion of the study area, and clear boundaries between pastures in terms of arbuscular mycorrhizal fungi (AMF) distribution. Soil physical and chemical properties were sufficiently correlated with biological measurements to predict soil microbial community size based on routine soil test analyses. The patterns of distributed elements evaluated in this study can provide a basis for management decisions on soil health and potential contaminant monitoring across the study area. These findings provide insight as to how novel, producer-designed soil health management practices in small semi-arid production systems impact soil properties, as well as help develop cost-effective predictive modeling solutions that aid long-term monitoring efforts. Such strategies will be critical tools in resource-scarce semi-arid regions such as those found in the current study region of Texas, as well as similar semi-arid regions such as northern China and northeastern Brazil. Overall, the results of this study provide direction for long-term soil health monitoring at this site, as well as a critical evaluation of relationships between soil health indicator measurements that aids interpretation and management planning.

ABSTRACT Defining a suitable soil tillage option that provides adequate soil physical conditions for optimum cassava (Manihot esculenta Crantz) productivity has not been adequately researched in southern Brazil. This study aimed to evaluate, in an Argissolo Vermelho-Amarelo Distrófico (Acrisol or Hapludalf), three tillage methods - conventional (inverting) tillage, chiseling, and long-term no-tillage (without and with, additional soil compaction), as affecting soil hydro-physical properties and cassava yield, in southern Brazil. Undisturbed and disturbed soil samples were collected from row and interrow positions, from the soil surface down to 0.40 m depth to determine soil bulk density, degree of compaction, porosity, water retention, plant available water, air and water permeability, mechanical properties (compressibility and elasticity), and chemical properties. The yield of cassava storage roots was obtained at crop physiological maturity. Conventional (inverting) and chisel tillage of soil previously under long-term no-tillage increased soil macroporosity - a composition or capacity physical property – of the surface soil, but did not improve the functioning/intensity properties air and water permeability. Soil reconsolidation over a short-time significantly affects soil structural condition, and thus soil tillage is not needed to improve soil structure. Additional compaction on the no-till soil causes detrimental consequences on composition/capacity and functioning/intensity physical properties. Nonetheless, neither improvement of soil structure by tillage nor further compaction affects cassava storage root yield in the sandy loam soil. Therefore, no-tillage is the best management system, in which soil loosening is done only during furrowing for cassava-stem planting.

ABSTRACT: Phosphorus (P) fixation in the soil reduces the utilization of this element by plants and can be one of the main problems for fertilization management in soils containing Fe oxides. As a strategy to minimize the effects of P retention, organic materials, such as biochar or commercial composts, may be useful tools to maintain P availability and delay immobilization of this element in the soil, thereby benefiting, for example, the rehabilitation of areas impacted by Fe mining. The objective of this study was to evaluate the kinetics of P sorption and desorption and the hysteresis index in red mining waste from Fe mining subjected to açaí biochar and commercial compost amendments. Therefore, a substrate collected from Fe mining waste piles in the Carajás Mineral Province was incubated for 30 days with açaí biochar, commercial compost, and açaí biochar + commercial compost at a ratio of 90 % mining waste and 10 % organic amendment (w/w). The P sorption and desorption kinetics were evaluated in a solution containing 10 mg L−1 P at times from 0.5 to 48 h; the data were modeled according to a pseudo-first-order equation considering two types of reaction sites, and the hysteresis index was obtained by the difference between the sorption and desorption isotherms. Treatment of the mining substrate with açaí biochar reduced P sorption, while P desorption was increased by up to 60 % by applying biochar and/or commercial compost. Açaí biochar also reduced the hysteresis of P sorption from 78 to 54.8 %, in addition to slowing P fixation in this substrate. Thus, this study showed that açaí biochar and commercial compost may maximize the benefits of phosphate fertilization during the rehabilitation of areas impacted by Fe mining. However, as these composts can cause different effects on P dynamics in mining waste, their effects on other elements, such as micronutrients, whose availability may be affected, are important to be evaluated.

ABSTRACT Oxisols ( Latossolos ) are widely distributed in tropical zones and generally characterized by high levels of surface and subsurface acidity. In Brazil, most Oxisols are managed under no-till conditions with surface application of acidity amendments. This study aimed to evaluate lime application strategies (incorporated and surface) for achieving the desired soil base saturation (BS%) levels (44, 60, 70, and 90 %) and the effect of phosphogypsum + lime application on soil chemical properties as well as wheat and corn yield in southern Brazil. Lime incorporation was more effective in reducing the soil acidity and increasing Ca2+ and Mg2+ despite a decrease in organic matter at the soil surface. Phosphogypsum application increased S-SO42- and Ca2+ availability throughout the deeper soil layers and reduced the Mg2+ content in the surface layer. Wheat yield under incorporated lime conditions increased with BS% up to 75, but there was no response to surface application. When phosphogypsum was applied, the wheat yield increased by 8.4 %. For corn, incorporated lime increased the yield up to 445 kg ha-1, which was equivalent to the yield after phosphogypsum application. An increase in the S-SO42- level was the main factor related to the increase in crop yields. In the short term, our results suggest that phosphogypsum applied along with lime is more appropriate than incorporating lime under no-till management conditions.

ABSTRACT Novel fertilizer stabilization technologies are needed to decrease ammonia (NH3-N) losses and increase nitrogen use efficiency. Duromide + NBPT is a new technology that combines two molecules, Duromide and NBPT, whose propose is to increase the efficiency of the urease inhibitor NBPT in reducing NH3-N loss from urea. Preliminary results showed that Duromide + NBPT can be a more effective product than just NBPT, particularly under low soil pH and high-temperature conditions. This study aimed to compare the effects of urea + Duromide + NBPT, urea + NBPT, and conventional urea on soil N losses by NH3-N volatilization. The field experiment was conducted on a Latossolo Vermelho Distroférrico (Oxisol) in Campo Mourão, Paraná, Brazil, using a randomized complete block design with treatments arranged in a 2 × 3 factorial, comprising two N doses (45 and 90 kg ha-1) and three N fertilizers (urea + Duromide + NBPT, urea + NBPT, and conventional urea). The NH3-N volatilization data were subjected to nonlinear regression using a logistic model. The NH3-N losses varied according to dose and fertilizer, reaching up to 12.4 % of the applied N in the conventional urea treatment. Urea + Duromide + NBPT was more efficient than urea + NBPT in decreasing NH3-N volatilization. Compared to conventional urea at doses of 45 and 90 kg ha-1 of N, urea + Duromide + NBPT reduced NH3-N volatilization losses by 35 and 54 % and from urea + NBPT by 15 and 33 %, respectively. The new stabilizing technology Duromide + NBPT reduced NH3-N losses by up to 33 % compared to NBPT alone. Ammonia volatilization was influenced by soil moisture. The volatilization peak, observed after 18-19 days of N fertilizer application, was triggered by rainfall events.

ABSTRACT Hydro-sedimentological models might be useful tools for investigating the effectiveness of soil and water conservation practices. However, evaluating the usefulness of such models requires that predictions are tested against observational data and that uncertainty from model parameterization is addressed. Here we aimed to evaluate the capacity of the SWAT model to simulate monthly streamflow and sediment load in the Posses creek catchment (12 km2), Southeast Brazil. The SUFI-2 algorithm from SWAT-CUP was applied for calibration, testing, uncertainty, and sensitivity analysis. The model was calibrated and initially tested using discharge and sediment load data, which were measured at the catchment outlet. Additionally, we used soil loss measurements from erosion plots within the catchment as independent data for model evaluation. Average monthly streamflow simulations obtained satisfactory results, with Nash-Sutcliffe coefficient (NSE) values of 0.75 and 0.51 for the calibration and testing periods, respectively. Sediment load simulations also displayed satisfactory results for calibration (NSE = 0.65) and testing (NSE = 0.52). However, the comparison with independent plot data revealed that SWAT severely overestimated hillslope erosion rates and compensated it with high sediment channel deposition. Moreover, the model was not sensitive to the parameters used for calculating hillslope sediment yields. Therefore, it should be used with caution for evaluating the interactions between land use, soil erosion, and sediment delivery. We found that the commonly used outlet-based approach for model calibration and testing can lead to internal misrepresentations, and models can reproduce the right answer for the wrong reasons.

ABSTRACT Soil acidity is one of the main factors that reduces productivity in agricultural crops, and it is corrected with materials that neutralize acidification. Among soils affected by acidity are those of volcanic origin. At least 30 % of agricultural soils in Chile are of volcanic origin, and acidity correction practices must be constantly performed. This study aimed to evaluate the effectively of two materials that may neutralize soil acidification and increase yield production in Chilean volcanic soils. An experiment was conducted during the 2019-2020 season, in which different acidity correction materials derived from the cellulose industry [Ash + Dregs (AD) and Ash + Dregs + Sludge (ADS)] were applied in three volcanic soils cultivated with wheat in southern Chile (Chillán, Temuco, and Osorno). Treatments were a control, CaCO3 at an adjusted rate to reach pH 6.0 and AD and ADS at the same rate as CaCO3 and twice the rate. Results indicated that the application of AD and ADS produced similar effects on pH(H2O), Ca2+, Mg2+, and Al3+ contents, cationic exchange capacity (CEC), and Al saturation compared with CaCO3 at the same rate; the effect was directly proportional to the rate used with each AD and ADS. Wheat production at each location was similar for AD, ADS, and CaCO3 at the same rate; however, it fluctuated between 10.1 and 10.4, 5.4 and 6.5, and 10.0 and 10.3 Mg ha-1 at Chillán, Temuco, and Osorno, respectively. Results indicate that these materials are an alternative to be used as a soil acidity correction amendment.

ABSTRACT Brazil is currently the leading country in no-till (NT) farming, particularly on Ferralsols (Latossolos), the most abundant soil type. These soils are characterized by subsurface acidity that cannot be effectively corrected by surface application of additives. In this situation, the use of phosphogypsum can be advantageous. This study aimed to assess the residual effects of lime and phosphogypsum application on a clayey Ferralsol, and four soybean and two wheat yields in southern Brazil. The area has been cultivated under no-till since 1975. The soil was limed to different base saturation (BS) levels (50, 60, 70, and 90 %) by surface application (SL) or lime incorporation (IL). Three combined treatments were also studied: (i) surface liming to 60 % BS plus standard (3.71 Mg ha-1) phosphogypsum dose (60G1), (ii) surface liming to 70 % BS + standard phosphogypsum dose (70G1); and (iii) surface liming to 70 % BS + double (7.42 Mg ha-1) phosphogypsum dose (70G2). Soil samples were collected 48 months after treatment. Soybean and wheat yield was not influenced by BS levels, however IL increased soybean yield in 2012/13, but reduced soybean and wheat yield in later crops. Phosphogypsum increased wheat yield by up to 12.8 % (2012 season) and 5.2 % (2015 season), but soybean was not influenced. Incorporated liming caused a decrease in soil Al3+ levels until 0.60 m depth, whereas SL decreased Al3+ levels until 0.30 m depth. Surface liming increased Mg2+ levels in the 0.40-0.60 m layer. Incorporated liming reduced soil organic matter in the surface layer. A double dose of phosphogypsum (7.42 Mg ha-1) had a greater residual effect in subsurface layers but caused a decrease in Mg2+ and K+ levels. Therefore, the standard phosphogypsum dose provided the best results. In the very clayey soil in subtropical environment, the effects of SL extend beyond surface layers and are preferable to those of IL, although production was not influenced by BS.

Abstract Vertisols presenting kaolinite codominance or prevalence were already reported in several countries worldwide. However, the literature has few studies focused on investigating the influence of this clay mineral in soil geotechnical behavior. This study aimed to carry out the characterization of Vertisols in Bahia State, Brazil, to understand the influence of physical, chemical, and mineralogical properties on their geotechnical behavior, as these soils have high natural fertility and have been used for agricultural activity, but with great risk due to their physical and geotechnical properties. Six Vertisols were selected, three located in Juazeiro County (Semiarid region) and the other three in Recôncavo region. Geotechnical characterization of selected soils was carried out in their respective diagnostic horizons by determining properties such as granulometric curve, Atterberg limits, clay activity, linear expansion coefficient, compaction capacity, cohesion (c), and internal friction angle (ϕ) of saturated soils. Soil expansion potential was associated with expansive clay contents and clay content in each soil sample. The best soil compaction efficiency was observed for kaolinitic Vertisol, which presented greater void ratio reduction and higher density due to moisture increase. In addition, c increased as kaolinite content also increased and decreased as clay content increased in soils presenting similar mineralogy. On the other hand, ϕ was influenced mainly by granulometry since higher sand and gravel levels enabled higher ϕ, regardless of clay type.

ABSTRACT A good soil fertility management for soybean production must consider the amount of nutrients that are exported by seeds. In recent decades, soybean yield has increased due to better crop management and genetic improvements, which may affect the amount of nutrients removed. Therefore, this study aimed (i) to analyze the relationship between the concentration of macronutrients in soybean seeds in Brazil with soybean yield and genotypes, and (ii) to update nutrient concentration values in soybean seeds for fertilizer recommendation purposes, comparing them with the values described in the main official fertilization recommendation systems used in Brazil. For this purpose, we used 3,017 observations obtained from 67 studies evaluating at least one macronutrient concentration [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S)] in soybean seeds in the last 45 years in Brazil (from 1974 to 2019). Results indicate that the concentration of macronutrients in soybean seed is affected by both soybean yield and genetic material. Modern genotypes of the Intacta Roundup Ready-2 group remove 15, 21, 18, 17, and 23 % more K, P, Ca, Mg, and S and 4 % less N compared to non-Roundup Ready genotypes. The increase in soybean yield was followed by an increase in the concentration of N and a decrease in the concentration of P and K in soybean seed. Data obtained from studies published between 2015 and 2019 indicates that soybean removes, on average, 57.2, 17.6, 5.5, 2.9, 2.6, and 2.5 kg Mg-1 of N, K, P, S, Ca, and Mg, respectively. These macronutrient concentrations in soybean seeds are in disparity with most reference values described in the official fertilization recommendation systems in Brazil, highlighting an urgent need to review the standard values for replacement fertilization of soybeans. Moreover, future studies should focus on the influence of genetics on soybean seeds composition to ensure high soybean productivity with rational use of fertilizers.