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Copyright of Revista Brasileira de Engenharia Agricola e Ambiental - Agriambi is the property of Revista Brasileira de Engenharia Agricola e Ambiental 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.)

Microbial biomass (MB) is an important indicator of soil quality, being responsive to changes resulting from soil management and use. Although there are studies that evaluate changes in soil microbiological attributes in coffee growing systems, the effects of these systems on MB and its relationship with other soil attributes have rarely been investigated, especially in tropical climate conditions at altitude. Therefore, this study aimed to evaluate the effect of different coffee growing systems on biomass and microbial activity and how these responses relate to other soil and litter attributes. Our study was carried out in soils under three Coffea arabica cultivation systems (CCM—monoculture, CCB—consortium with banana, AFS—agroforestry system with Grevillea robusta) and under native forest (NF). Soil samples were collected at a depth of 0–10 cm and subjected to analysis to determine the microbial biomass carbon content (MB-C) by the fumigation-extraction method, accumulated respiration through released CO2, soil organic carbon (SOC) and labile carbon by wet oxidation. There was a 45% reduction in SOC in coffee growing systems and a 75% reduction in MB-C in CCM compared to NF. The AFS is closer to native forest conditions due to its positive influence on the SOC content and the efficiency of converting this carbon into microbial carbon. The presence of the forestry component is positive and should be encouraged to mitigate the impacts of coffee growing on the soil. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) is known to vary among different ecosystems and soilscapes, yet the degree of variation remains uncertain. Comparing SOC levels in undisturbed ecosystems like forests with those in gradually altered ecosystems can provide valuable insights into the impact of land use on carbon dynamics. This study aimed to evaluate the effects of different land uses on soil fertility parameters in the tropical region of Kerala, focusing on forests as well as cultivated agricultural landscape such as coconut, pepper, tapioca, acacia plantations, and mixed home garden cropping systems. Significant variations were observed among different crops and land use systems in terms of soil fertility. Forests exhibited the highest SOC content at 3.78 g kg−1, while acacia plantations showed the lowest at 0.76 g kg−1. Additionally, various soil properties such as different carbon fractions (e.g., humic acid, fulvic acid), total nitrogen, carbon, available nutrients, physical properties, aggregate size fractions, microbial biomass carbon, and spectral signatures differed significantly across the different land uses. These findings suggest a decline in soil fertility in altered ecosystems compared to adjacent forest soils, highlighting the vital role of forests in conserving natural resources and maintaining soil health. In addition, among the different landscapes studied, mixed cropping systems of home gardens sustained soil fertility better than monocropping systems. The observed variations in soil physicochemical properties among different land use types indicate a threat to sustainable crop production. Effective management practices aimed at improving soil fertility and sustaining crop production in these altered ecosystems are essential. This study highlights the importance of adopting appropriate management strategies to conserve soil health and ensure sustainable crop production in tropical landscapes like Kerala. The holistic approach adopted in this study, encompassing a wide range of soil fertility parameters across various land uses, along with its implications for sustainable land management, adds significant novelty and relevance to the existing literature on soil dynamics in tropical regions like Kerala. [ABSTRACT FROM AUTHOR]

In tropical regions, pedogenesis studies are challenging since most soils are polygenetic and studies on this approach are still lacking. Thus, complementary data is needed to understand their formation, which has been possible through proximal sensing tools. The objective of this study was to assess the efficiency of proximal sensing data to investigate the presence of lithological discontinuities and the within-profile variation of polygenetic soils formed from different parent materials and with varying weathering degrees. Soil morphology, texture, fertility, mineralogy, and reflectance analyses were conducted to characterize soil samples collected per horizon from five studied profiles. Additional samples were collected following a 15 x 15 cm grid and analyzed via portable X-ray fluorescence (pXRF) spectrometry. Parent material discontinuities were investigated through the ratios Ti/Zr, Si/Al, fine sand/coarse sand (FS/CS), and differences in the mineralogy of the sand, silt, and clay fractions. The five studied profiles were classified as: Fluvic Cambisol (CY), Sideralic Cambisol (CX), Xanthic Gibbsic Ferralsol (LA), Xanthic Ferralsol (LVA), and Rhodic Gibbsic Ferralsol (LV) per the World Reference Base (WRB/FAO) for Soil Resources. pXRF data revealed within-horizon variation of elemental contents. Chemical traits of anthropic and pedogenetic origin were successfully identified. The Ti/Zr ratio and mineralogical analysis of the sand, silt, and clay fractions were able to identify parent material discontinuities in LVA. By interpreting Vis-NIR spectra, it was possible to separate soils based on texture and mineralogy. Proximal sensor data, especially from pXRF, allowed for the detection of parent material discontinuities that were unapparent during field morphology analysis, contributing to improved details on soil genesis assessment and comprehension of previous soil formation events.

Nitrogen (N) is highly reactive and prone to being easily lost into the air and soil water. Biochar–N composites have proven effective in nourishing and improving maize growth. The aim of this study was to synthesize and assess the properties of composites made from biochars (pyrolyzed at 300 °C) derived from chicken manure (N = 3.5%) and leguminous cake (N = 9%) and enriched with ammonium sulfate (AS), urea, and diammonium phosphate (DAP). The biochar pH was adjusted to approximately 6 using sulfuric and phosphoric acids prior to formulating the six tested composites. Maize was cultivated for 50 days under greenhouse conditions, with evaluations of the maize dry matter (DM) and N in the plant shoot. The biochar and composite properties underwent scrutiny for chemical and physicochemical attributes, as well as for soluble N in water and in an HCl solution. Throughout maize cultivation, the release of N as ammonium and nitrate from the composites and pure biochars in the Oxisol solution was successively assessed. Composites formulated with DAP and supplied at a dose of 270 mg kg−1 N yielded the same maize dry matter as composites in which 400 mg kg−1 N was supplied to plants. Regardless of the N source, at the end of maize cultivation, the residual N in the Oxisol was reduced and inadequate for a new cultivation, even in soils treated with urea. Notably, the biochar–N composites, particularly those formulated with DAP, were as effective as urea in nourishing and promoting robust maize growth. In contrast, the maize biomass was lower for plants fertilized with pure biochars, indicating that the N from the carbonized matrices was insufficient for optimal biomass production. [ABSTRACT FROM AUTHOR]

Crop yield variations in the Orinoquía region - Colombia, are primarily associated with extreme precipitation events. Therefore, studying crop water supplies under naturally variable climate conditions is fundamental in an actual climatic change context. Rainfall data collected in the Quenane sub-basin were analyzed to understand the soil water dynamics in the Orinoco catchment. The basin covers 179 km2 and consists of the piedmont landscape (Eastern Mountain Range) of the Villavicencio Municipality, Department of Meta. This study analyzes the rainfall variability using Pearson correlation analysis, the Mann-Kendall trend analysis, and soil water balance to determine the implications of these factors in crop performance at the basin scale. The results indicated that the spatial distribution of rainfall in the basin responds to a longitudinal average variation of precipitation and that this response is more accentuated (i.e., greater rainfall) toward the west of the basin. Despite the basin being located in the tropical zone, no evidence was found regarding the effect of the El Niño Southern Oscillation on rainfall patterns. Yet, the temporal analysis revealed some years with extreme rainfall values and high-uncertainty levels during transitions between wet and dry periods. During these transition periods, a greater potential for effects on farm yields exists due to the variable cumulative rainfall observed during recent years. The time series trend analysis revealed changes in rainfall patterns at different scales (weekly and yearly) and distribution based on the decrease of rainy days per week and year. This trend is much more accentuated during the second half of the year, generating uncertainty and reducing farm yields throughout the basin. [ABSTRACT FROM AUTHOR]

ABSTRACT Soil fauna organisms participate in a series of processes that benefit the physical and chemical soil properties; however, little is known about their spatial variability and scale. This study aimed to characterize the spatial variability of soil fauna from multifractal and joint multifractal analysis in Brazilian Savanna areas. Pitfall traps collected soil fauna in two Savanna formations (dense Savanna and typical Savanna) in two transects with 128 points. Organisms were identified and classified into functional groups (Microphages, Pollinators, Predators and Social), and then Ind trap−1 day−1 (number of individuals per day in the sample) and Richness were determined. Data were analyzed using multifractal and joint multifractal analysis, and the scale indexes f(α,β) were generated for the singularity indexes of α(q,t) and β(q,t), considering Ind trap−1 day−1 and Richness as predictive variables. A total of 3456 and 1629 individuals were collected from T1 (dense Savanna) and T2 (typical Savanna), respectively. The singularity spectrum for soil fauna showed the greatest difference in dimensions D−10–D10 for the functional group Pollinator (D−10–D10 = 0.936) in T1 and for Social (D−10–D10 = 0.620) in T2, reflecting more heterogeneous systems. The joint multifractal dimension showed a high correlation between Ind trap−1 day−1 and the functional groups (Pollinators, Predators, and Social) in T1, demonstrating how phytophysiognomy of this experimental plot (dense Savanna) favors the presence of these organisms and reflects the spatial correspondence of the measurement values along the geometric support. Abundance of organisms (Ind trap−1 day−1) and Richness were promising variables to represent the set of relationships with the functional groups of soil invertebrate fauna. In general, multifractal analysis using abundance and Richness can assist in decision-making focused on conserving Savanna areas.

The Wanakah Formation and Tidwell Member of the Morrison Formation record intervals of paedogenesis in the Paradox Basin and Central Colorado trough, western Colorado during the Middle-Late Jurassic. Detailed field description of paleosols and paedogenic carbonates at different stratigraphic horizons from three localities document four main pedotypes: vertisols, gleysols, oxisols, and protosols. Generally, gleysols reflect reducing conditions, protosols and oxisols reflect oxidizing conditions, and vertisols reflect fluctuations in oxidizing/reducing conditions (seasonality). Major elemental geochemical ratios in samples from these paleosols suggest variable redox conditions and a sub-humid to humid paleoclimate with seasonal precipitations during paleosol development. Estimated mean annual temperature based on elemental analyses of paleosol B in paleosols from Ribbon Trail and Escalante Canyon in western Colorado suggest mesic – thermic paleoclimate. Mean annual precipitation indicates sub-humid to humid regional palaeoclimatic conditions marked by seasonal precipitation. Clay mineralogy of these paleosols, determined by X-ray diffraction, shows the abundance of illite most likely formed from smectite alteration due to episodic wetting and drying. δ13C and δ18O isotope analyses of carbonate veins in these paleosols suggest that they formed recently from meteoric water and therefore are not considered for palaeoclimatic reconstructions. Mean annual temperature and mean annual precipitation estimates in the Wanakah Formation and Tidwell Member of the Morrison Formation provide new information on the local and regional palaeoclimatic and paleoenvironmental conditions during the Middle Jurassic in western Colorado as well as data for comparison with the Upper Morrison paleoclimate from northern and southern localities in the western United States. [ABSTRACT FROM AUTHOR]

Copyright of Revista Foco (Interdisciplinary Studies Journal) is the property of Revista Foco 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.)

We investigated how organic matter may, directly and indirectly, modify the porosity of Ferralsols, that is, deeply weathered soils of the tropics and subtropics. Although empirical and anecdotal evidence suggests that organic matter accumulation may increase porosity, a mechanistic understanding of the processes underlying this beneficial effect is lacking, especially so for Ferralsols. To achieve our end, we leveraged the fact that the Profundihumic qualifier of Ferralsols (PF) is distinguished from Haplic Ferralsols (HF) by both a much larger average carbon content in the first 1 m of soil depth (19 kg C m−3 in PF vs. 10 kg C m−3 in HF) and a significantly lower bulk density (1.05 ± 0.08 kg L−1 in PF vs. 1.21 ± 0.05 kg L−1 in HF). Through exhaustive modelling of carbon – bulk density relationships, we demonstrate that the lower bulk density of PF cannot be satisfactorily explained by a simple dilution effect. Rather, we found that bulk density correlated with carbon content when combined with carbon: nitrogen ratio (r2 = 0.51), black carbon content (r2 = 0.75), and Δ14C (r2 = 0.81). Total pore space was greater in PF (61 ± 3%) than in HF (55 ± 2%), but x‐ray computed tomography revealed that pore space inside soil aggregates of 4–5 mm diameter does not vary between the studied Ferralsols. We further observed nearly twice as many roots and burrows in PF compared with HF. We thus infer that the mechanism responsible for the increase in porosity is most likely an enhancement of resource availability (e.g., energy, carbon, and nutrients) for the organisms (earthworms, ants, termites, etc.) that physically displace soil particles and promote soil aggregation. As a result of increased resource availability, soil organisms can create especially the mesoscale structural soil features necessary for unrestricted water flow and rapid gas exchange. This insight paves the way for the development of land management technologies to optimize the physical shape and capacity of the soil bioreactor. [ABSTRACT FROM AUTHOR]

In the 1960s, a conservationist agricultural practice known as a "no-tillage system" was adopted. Several benefits such as soil erosion reduction and soil carbon sequestration, among others, could be ascribed to no-till systems. Therefore, it is important to evaluate the long-term sustainability of this agricultural system in different environments. This study has the objective to evaluate the soil organic carbon dynamic in a no-till system (40-year) and on a rolling landscape in Southern Brazil. A systematic grid with four transversal–longitudinal transects was used for soil sampling. Soil samples from 0–20, 20–40, and 40–60 cm depths were collected (16 trenches × 3 depths × 1 sample per soil layer = 48), and a forest nearby was used as control (4 trenches × 3 depths × 1 sample = 12). The soil at the forest site showed 20% more carbon stock than no-till at the 0–20 cm soil depth. However, the entire no-till soil profile (0–60 cm) showed similar soil carbon as forest soil. The soil carbon stock (0–20 cm) in no-till was depleted at a rate of 0.06 kg C m−2 year−1, summing up to a carbon loss of 2.43 kg C m−2. In addition, the non-uniform hillslope affected the soil carbon redistribution through the landscape, since the convex hillslope was more depleted in carbon by 37% (15.87 kg C m−2) when compared to the concave sector (25.27 kg C m−2). On average, the soil carbon loss in the subtropical agroecosystem was much lower than those reported in literature, as well as our initial expectations. In addition, the no-till system was capable of preserving soil carbon in the deepest soil layers. However, presently, the no-till system is losing more carbon in the topsoil at a rate greater than the soil carbon input. [ABSTRACT FROM AUTHOR]

Wetting and drying (W-D) cycles are responsible for significant changes in soil structure. Soil often undergoes irreversible changes affecting infiltration and solute retention through W-D cycles. Thus, it becomes essential to evaluate how soils under natural conditions are altered by W-D cycles. This study analyzed two non-cultivated (from grassland and secondary forest) Oxisols (Typic Hapludox and Rhodic Hapludox) of different textures under 0 and 6 W-D cycles. The main results obtained showed that soil water retention was mainly affected in the driest regions (smaller pore sizes). The contribution of residual pores to total porosity increased with 6 W-D and transmission pores decreased in both soils. The Rhodic Hapludox presented differences in water content at field capacity (increase), while the Typic Hapludox showed alterations at the permanent wilting point (increase), affecting the amount of free water (Rhodic Hapludox) and water available to plants (Typic Hapludox). Both soils showed increases in imaged porosity with 6 W-D. Variations in the contribution of small and medium rounded pores, mainly large and irregular (with an increase in both soils not significant in the Rhodic Hapludox), could explain the results observed. The micromorphological properties were mainly influenced by changes in the number of pores, in which smaller pores joined, forming larger ones, increasing the areas occupied by larger pores. Overall, this study showed that the investigated soils presented pore systems with adequate water infiltration and retention capacities before and after continuous W-D cycles. [ABSTRACT FROM AUTHOR]

Abstract The objective of this work was to investigate changes in soil chemical characteristics, phosphorous concentrations in maize leaves, and the agronomic efficiency (AE) of magnesium thermophosphates produced from rocks of the Maicuru complex in the Brazilian Amazon Basin, in comparison with triple superphosphate (TSP). The thermophosphates consisted of a mixture of raw material from apatite, dunite, and quartz sandstone from Maicuru, aiming to adjust the contents of P, Mg, and Si. The mixture was melted, ground, and subjected to the analysis of solubility, chemical characteristics, and granulometry. The experiment consisted of two rates of dolomitic lime (0 and 2.4 Mg ha-1), three rates of P (20, 60, and 100 mg kg-1 soil), and four sources of P (TSP and three Mg thermophosphates), as well as of two control treatments, with and without lime. Three replicates were carried out per treatment in pots containing plants of the BR 5107 maize hybrid. Phosphorous concentration was determined in maize leaves at 45 days after sowing. The Mg thermophosphates showed a high AE and a higher neutralizing effect with the application of lime, which improved soil chemical characteristics and AE. The thermophosphates obtained from rocks of the Maicuru complex can be an alternative P fertilizer in maize production.

The conversion from native forest to other land-use systems can decline the soil organic carbon (SOC) in tropical soils. However, conservationist management could mitigate SOC losses, promoting the functioning and stability of agricultural soils. This study aimed to address the influence of conversion from native forest to different land-use systems on SOC fractions in Northeastern Brazil. Topsoil soil samples were collected in areas under pasture (PAS), no-tillage (NT1 and NT2), eucalyptus (EUC), and native forests of Cerrado in Northeastern, Brazil. Total organic C, microbial biomass (MBC), particulate (POC), and mineral-occluded organic C (MOC), as well as fulvic acids (C-FA), humic acids (C-HA), and humin (C-HUM) fractions were accessed. The results showed that land conversion maintained similar levels of humic fractions and total organic carbon (TOC) stocks in the PAS, NT1, NT2, and EUC as compared to native Cerrado. Soils with the input of permanent and diverse fresh organic material, such as NT2, PAS, and EUC, presented high levels of MBC and POC, and the lowest C-FA:TOC and C-HA:TOC ratios. The land conversion to agricultural systems that include cropping rotations associated with pasture species such as Mombasa grass and eucalyptus prevents topsoil losses of active C compartments in the Cerrado of the Brazilian Northeast. It suggests that sustainable and conservationist management should be emphasized to maintain and improve the status of soil organic C. [ABSTRACT FROM AUTHOR]

Erosion-soil loss is responsible for long-term environmental impacts due to water resource silting process and biodiversity loss. Studies focusing in erosion-soil loss are important for understanding phenomena affecting the environment. Therefore, this study aimed to analyze and characterize the susceptibility to soil erosion in drainage basins in the municipality of Jataí, located in the southwest of the state of Goiás/Brazil (used as case study model). The places most susceptible to soil losses in the studied context are located in the northwest, southwest and southeast regions of Jataí. The rainfall erosivity (R) indices in the period from 2000 to 2020 were classified as medium (500–750 tn mm ha−1 year−1), high (750–1000 tn mm ha−1 year−1) and very high (> 1000 tn mm ha−1 year−1). With regard to soil erodibility (K), the most prone to erosion are the entisol with a K value of around 0.029 t/ha MJ−1 mm−1 and the entisol with 0.041 t/ha MJ−1 mm−1. As for the topographic factor (LS), values between 3.3 and 5.5, considered moderate, occupy 317.88 km2; the ranges between 5.5 and 7.5, representing 57.69 km2, are considered to have moderately strong susceptibility. Although 46.14% of the analyzed basins have mild-to-moderate susceptibility (FAO), in an area of just over 1316.46 km2 (18.35%), there are susceptibilities of severe to very severe, formed by the soils entisol, ultisol and oxisols, with slopes between 45 and 75%. This study demonstrated to be useful for proposing environmental monitoring policies of drainage basin areas affected by erosion. [ABSTRACT FROM AUTHOR]

Improving and preserving soil quality in areas managed under no-tillage, especially in clayey soils, is extremely important for achieving high productivity along with environmental preservation. In this study, we evaluated the effect of three states of soil compaction and initial water saturation on pre-consolidation pressure (σp) and compaction index (CI) of two Oxisols, in order to estimate maximum loads to be applied by pneumatic machinery and agricultural implements without causing irreversible damage to soil structure. Oxisol-LVd (0.55 kg kg−1 clay) and Oxisol-LVdf (0.62 kg kg−1 clay) soils from the plateau region of Rio Grande do Sul were studied. An isoline map was generated for soil penetration resistance in the 0.07–0.12 m soil layer, with the highest state of compaction. Soil bulk density was used to characterize three state of compaction, used as treatments. Statistical analysis consisted of comparing soil σp and CI means for state of compaction, initial water saturation, and soil layers. Increase in clay content and bulk density and reduction in soil moisture is associated with increase in soil σp and decrease in CI. Average values of critical σp of the three states of compaction at field capacity are 245 kPa for Lvd, and 347 kPa for LVdf. In an annual timeframe for already consolidated no-tillage Oxisols, further soil wheeling and natural reconsolidation does not affect soil pre-consolidation and compaction susceptibility. [ABSTRACT FROM AUTHOR]

The agronomic efficiency of biochar-based fertilizers (BBFs) relies on the synthesis routes, properties, and interaction with the soil–plant system. In our study, BBFs were produced from coffee husk, low-grade acidulated phosphate rock with and without the addition of magnesium (Mg). BBFs were characterized for infrared analysis and the kinetics of phosphorus (P) release in water or citric acid (CA). The agronomic performance of BBFs was tested by growing maize and, in sequence, brachiaria grass in pots filled with two Oxisols with contrasting soil organic matter (SOM) content. Using the same chemical stoichiometric ratio, nitric acid was more effective than hydrochloric and sulfuric acids, creating BBFs with enhanced agronomic performance. The use of Mg in the BBFs synthesis reduced the P released in water. Phosphorus released in CA leachates positively correlated with the P in the shoot of both plants. BBFs produced using nitric acid had higher residual effect on brachiaria grass grown in the Oxisol with the highest SOM. Our outcomes show that the P rate for maize and brachiaria grass should be considered based on P soluble in neutral ammonium citrate plus water in BBFs. BBFs is an alternative to improve the use efficiency of P in Oxisols. [ABSTRACT FROM AUTHOR]

ABSTRACT The aim of this work was to increase the aerial part, biometry, and yield of achenes from sunflower plants on the effect of increasing doses of blood residue, as an alternative source of phosphorus (P), in a clayey-textured red Oxisol. The experimental design used was randomized blocks, with six treatments and four replications. The treatments consisted of five doses of blood residue (0, 6, 12, 24 and 48m3 ha-1) and a control treatment that received phosphate chemical fertilization, 80kg ha-1 of P2O5. The increasing doses of blood residue and chemical fertilization do not show disproportionality for P concentration in soil, leaf, plant height (PH), stem diameter (SD), chapter diameter (CD) and achene production. The analysis of the principal component (PC) revealed that the first PC presents the greatest accumulated variation (74%). Based on the first PC, the dose of 12m-3 ha-1 has greater influence for PH, SC, and CD. Due to the greater influence on the biometric characteristics of sunflower plants, the blood residue (12m-3 ha-1 = 98.4kg P ha-1), can be used as an alternative source of phosphorus for the cultivation of sunflower in clayey oxisols.

A growing demand for resources has led to the expansion of agricultural areas worldwide. However, land conversion associated with poor soil management might lead to soil physical degradation. We investigated the effects of land conversion on soil physical properties in the Brazilian Cerrado region, under native Cerrado vegetation (NV)—pasture (PA) and NV—cropland (CL) conversion scenarios. Soil physical properties related to compaction, pore size distribution, and structure stability were assessed up to a 30 cm depth. Additionally, carbon levels of soil organic matter fractions (particulate and mineral-associated organic matter) were determined. Our results indicate that the compaction process equivalently reduced the soil porosity in PA and CL. However, soil penetration resistance was higher in PA (~2.5 MPa) than in CL (~1.5 MPa), as well as the stable mean weight diameter of soil aggregates. The highest total and labile organic carbon levels were observed in CL, while the lowest levels of total and labile organic carbon occurred in PA (smaller than in CL). These results suggest that the higher structural stability found in PA was mediated by the predominance of stabilized carbon (a decrease in the proportion of soil labile carbon), causing the gaining of soil strength under negligible soil volume variation (in comparison with CL). Our results suggest that the reduction in the soil porosity by compaction due to PA and CL uses can equivalently reduce macropore space and soil hydraulic functioning, and that soil carbon quality alterations (i.e., labile vs. stabilized fractions) are responsible for the gain in soil strength in long-term degraded PA areas. Future research should focus on understanding the magnitude in which soil organic matter controls soil physical attributes, such as soil strength in these expansion areas, and whether this gain in soil strength limits plant development and compromises productivity in the long term. [ABSTRACT FROM AUTHOR]

Cohesive Oxisols are widely used for cultivating eucalyptus in the Coastal Tablelands of the northeastern region of Brazil. However, mechanization and plant cultivation in these soils are difficult because of their cohesive layers. Therefore, the objective of this study was to identify better combinations between tillage systems and types of fertilization to improve the physical attributes of cohesive soil, with the aim of improving eucalyptus growth. The experimental design was completely randomized in a 4 × 2 factorial scheme (soil preparation × fertilization). The tillage systems tested were: i) conventional tillage (CT) - one plowing combined with two harrowings, ii) minimum tillage (MT) - subsoiling down until 0.57 m depths in the planting line, iii) no-tillage type 1 (NT1) - planting in 0.3 m-deep pits, and iv) no-tillage type 2 (NT2) - planting in 0.6 m-deep pits. The types of fertilization tested were mineral (MF) and organic fertilization (OF). The diameter of the soil aggregates was reduced after being subjected to any combination of cohesive soils. Furthermore, OF provided the best levels of plant-available water, attenuating the adverse conditions of the cohesive layer. MT, NT1, and NT2 improved the soil physical attributes when compared to CT. Therefore, the combination of either NT1 or NT2 with OF, followed by the combination of either NT1 or NT2 with MF, was determined to be the best way to cultivate eucalyptus on cohesive soils. [ABSTRACT FROM AUTHOR]

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 benefits of manure as a source of nutrients for plants and to improve soil quality are well‐known. Monitoring of manure application is needed if environmental issues are to be prevented. In particular, the availability and accumulation of phosphorus (P) has to be subject to rigorous monitoring. This study aims to both evaluate the efficacy of the resin method in extracting inorganic labile P in soils under the long‐term application of dairy liquid manure (DLM), and verify the influence of DLM on the recovery of applied P and soil legacy P. To realize our objectives, two long‐term field experiments were established under a no‐tillage system with annual DLM application on sandy clay loam (sandy Oxisol) and clayey (clayey Oxisol) soils. Treatment consisted of DLM applications (0, 60, 120, 180 m3 ha−1 year−1), independent of mineral fertilizer. Soil samples were taken from the 0–5, 5–10 and 10–15 cm layers after 10 years from the beginning of the trial. A single extraction with resin underestimated inorganic labile P; however, successive extractions were able to take up 43% and 26% of the total P in sandy and clayey Oxisols, respectively, whereas in a single extraction the take‐up was 17% and 8% from the same soils, respectively. The resin method was more effective in extracting P from the sandy Oxisol. Thus, when interpreting soil P contents for fertilizer planning, the soil texture should be taken into account. DLM application decreased P recovered from applied P, ranging from 54% to 83% (sandy), and 43% to 67% (clayey), and substantially increased soil legacy P. [ABSTRACT FROM AUTHOR]

Soil structure controls soil hydraulic properties and is linked to soil aggregation processes. The aggregation processes of Oxisols are controlled mainly by clay mineralogy and biological activity. Computed microtomography (µCT) may be a tool for improving the knowledge of the hydraulic properties of these soils. Thus, this study brings an advance in the use of 3D image analysis to better comprehend the water behavior in tropical soils. In this work, three Oxisols were studied with the objective to (i) characterize the soil water retention curve (SWRC), the corresponding pore size frequency, and the saturated hydraulic conductivity (Ksat); (ii) use µCT to obtain, based on 3D images of soil structure and pore size distribution; and (iii) correlating parameters from SWRCs, Ksat, and µCT with other physical-hydric, chemical, and mineralogical attributes. Rhodic Haplustox—P1, Anionic Acrustox—P2, and Typic Hapludox—P3 were the three studied Oxisols. The differences among the SWRCs were related to the microgranular and block type's structure morphology, which modified the soil pore space. The pore size frequency was calculated from SWRCs for pores with diameters of 87 ± 2 μm in P1, 134 ± 11μm in P2, and 175 ± 18 μm in P3. Pore size distribution from µCT was determined for the range of 20–100 µm, mainly with the highest percentages: 12 ± 1.09% for P1 and 12 ± 1.4% for P2. Pore connectivity was assessed from images by calculating Euler Numbers (EN), with the differences related to the biggest pore (ENbigpore): P1 (−44,223 ± 10,096) and P2 (−44,621 ± 12,573) showed more connected pores (ENbigpore) in comparison to P3 (−11,597 ± 6935). The parameter ENbigpore was decisive in understanding the water retention and conduction processes of the studied soils. The better-connected pore space increased Ksat in P1 (220 ± 0.05 mm h−1) and P2 (189 ± 0.1 mm h−1) in comparison to P3 (20 ± 0.3 mm h−1) and modified the shape of SWRCs. [ABSTRACT FROM AUTHOR]

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The objective was to chemically characterize and determine the ionic species of nutrients in percolated water from Oxisol, with application of Phosphogypsum and Gypsite. The experiment was carried out in a greenhouse, applying Phosphogypsum and Gypsum at doses from 0.0 to 4.0 t ha-1. Fifty-five days after application, a 60 mm rainfall simulation was simulated and the pH, conductivity, and content of calcium, magnesium, potassium, nitrogen, phosphorus, sulfur, sodium, and ionic speciation in the percolated water were analyzed. The definition of the source and adequate dose of gypsum for each soil favors less loss of nutrients in the percolated water. This implies that production costs related to plant nutrition do not increase. [ABSTRACT FROM AUTHOR]

Despite the increasing adoption of proximal sensors worldwide, rare works have coupled proximal with remotely sensed data to spatially predict soil properties. This study evaluated the contribution of proximal and remotely sensed data to predict soil texture and available contents of micronutrients using portable X-ray fluorescence (pXRF) spectrometry, magnetic susceptibility (MS), and terrain attributes (TA) via random forest algorithm. Samples were collected in Brazil from soils with high, moderate, and low weathering degrees (Oxisols, Ultisols, Inceptisols, respectively), and analyzed by pXRF and MS and for texture and available micronutrients. Seventeen TA were generated from a digital elevation model of 12.5 m spatial resolution. Predictions were made via: (i) TA; (ii) TA + pXRF; (iii) TA + MS; (iv) TA + MS + pXRF; (v) MS + pXRF; and (vi) pXRF; and validated via root mean square error (RMSE) and coefficient of determination (R2). The best predictions were achieved by: pXRF dataset alone for available Cu (R² = 0.80) and clay (R2 = 0.67) content; MS + pXRF dataset for available Fe (R2 = 0.68) and sand (R2 = 0.69) content; TA + pXRF + MS dataset for available Mn (R2 = 0.87) content. PXRF data were key to the best predictions. Soil property maps created from these predictions supported the adoption of sustainable soil management practices. [ABSTRACT FROM AUTHOR]

Solanum paniculatum L., a species endemic to tropical America and used in folk medicine in the treatment of anemia, hepatic and digestive disorders, has been widely studied. However, to date, no previous studies on correlations between the contents of mineral nutrients in plant roots with their contents in soil have been reported. The aim of this study was to determine the main mineral nutrients found in S. paniculatum roots and the soil in their natural habitat. It was observed that S. paniculatum roots grow in soils rich in calcium and had a positive correlation in the concentration of Ca with Fe, Na and K and a negative correlation with Zn and Mg. The results contribute to the knowledge of mineral nutrients in S. paniculatum as well as to its cultivation.

Copyright of Agronomía Colombiana is the property of Universidad Nacional de Colombia 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.)

Water erosion is one of the main forms of soil degradation, causing economic, environmental, and social damage. This study evaluated the effects of different formation stages of gullies (initial - IG; juvenile- JG; mature - MG; and senile - SG) on the chemical, organic carbon and microbiological attributes of soil, using a secondary forest (SF) and two areas of pasture as references in the “Mar de Morros” environment of the Brazilian Atlantic Forest biome. Soil samples (depth 0–0.05 m) were collected at the end of the rainy and dry seasons. Gullies in different stages of formation promote a decrease in soil fertility and modification of microbiological attributes, particularly when compared with secondary forest areas. Reductions of over 60% in total organic carbon (TOC), oxidizable organic carbon (POXC), FDA activity, β-glycosidase, acid phosphatase, C and N from microbial biomass, basal soil respiration (BSR) and glomalin-related soil protein (GRSP) were observed in gullies in early (IG) and intermediate (JG and MG) stages when compared to SF. It was found that the effect of erosion on soil chemical and microbiological attributes is more intense in gullies in the initial and intermediate stages compared with those in the senile stage (SG). Using multivariate PCA, the microbiological and chemical attributes of the soil are discriminated between gullies with distinct formation stages. Chemical attributes, TOC, POXC, FDA activity, β-glycosidase, acid phosphatase, MBC and MBN, BSR, and GRSP are good indicators for evaluating the process of erosion stabilization in gullies.

Abstract The objective of this work was to determine pedotransfer functions to predict water retention at the -33 and -1500 kPa matric potentials of soils under Cerrado, in the south of the state of Mato Grosso, Brazil. Samples (n=156) were collected for model calibration (n=124) and validation (n=32). A stepwise multiple regression was used to determine pedotransfer functions. Willmott’s index of agreement, root-mean-square error, Pearson’s correlation coefficient, and the confidence index were used to evaluate the performance of the functions and to compare them with those described in the literature. The most efficient variables to estimate water retention were: microporosity, total sand, and clay at -33 kPa; and total sand, silt and clay at -1500 kPa. The regional pedotransfer functions explained more than 94% of water retention variance in the studied soils. The reliability of the functions to predict water retention increased, at -33 kPa, with the use of the structural property microporosity and, at -1500 kPa, with the use of granulometric parameters. The studied regional pedotransfer functions predict water retention at the -33 and -1500 kPa matric potentials of soils under Cerrado, in southern Mato Grosso, better than the functions described in the literature.

In the 1960s, a conservationist agricultural practice known as a “no-tillage system” was adopted. Several benefits such as soil erosion reduction and soil carbon sequestration, among others, could be ascribed to no-till systems. Therefore, it is important to evaluate the long-term sustainability of this agricultural system in different environments. This study has the objective to evaluate the soil organic carbon dynamic in a no-till system (40-year) and on a rolling landscape in Southern Brazil. A systematic grid with four transversal–longitudinal transects was used for soil sampling. Soil samples from 0–20, 20–40, and 40–60 cm depths were collected (16 trenches × 3 depths × 1 sample per soil layer = 48), and a forest nearby was used as control (4 trenches × 3 depths × 1 sample = 12). The soil at the forest site showed 20% more carbon stock than no-till at the 0–20 cm soil depth. However, the entire no-till soil profile (0–60 cm) showed similar soil carbon as forest soil. The soil carbon stock (0–20 cm) in no-till was depleted at a rate of 0.06 kg C m−2 year−1, summing up to a carbon loss of 2.43 kg C m−2. In addition, the non-uniform hillslope affected the soil carbon redistribution through the landscape, since the convex hillslope was more depleted in carbon by 37% (15.87 kg C m−2) when compared to the concave sector (25.27 kg C m−2). On average, the soil carbon loss in the subtropical agroecosystem was much lower than those reported in literature, as well as our initial expectations. In addition, the no-till system was capable of preserving soil carbon in the deepest soil layers. However, presently, the no-till system is losing more carbon in the topsoil at a rate greater than the soil carbon input.

Wetting and drying (W-D) cycles are responsible for significant changes in soil structure. Soil often undergoes irreversible changes affecting infiltration and solute retention through W-D cycles. Thus, it becomes essential to evaluate how soils under natural conditions are altered by W-D cycles. This study analyzed two non-cultivated (from grassland and secondary forest) Oxisols (Typic Hapludox and Rhodic Hapludox) of different textures under 0 and 6 W-D cycles. The main results obtained showed that soil water retention was mainly affected in the driest regions (smaller pore sizes). The contribution of residual pores to total porosity increased with 6 W-D and transmission pores decreased in both soils. The Rhodic Hapludox presented differences in water content at field capacity (increase), while the Typic Hapludox showed alterations at the permanent wilting point (increase), affecting the amount of free water (Rhodic Hapludox) and water available to plants (Typic Hapludox). Both soils showed increases in imaged porosity with 6 W-D. Variations in the contribution of small and medium rounded pores, mainly large and irregular (with an increase in both soils not significant in the Rhodic Hapludox), could explain the results observed. The micromorphological properties were mainly influenced by changes in the number of pores, in which smaller pores joined, forming larger ones, increasing the areas occupied by larger pores. Overall, this study showed that the investigated soils presented pore systems with adequate water infiltration and retention capacities before and after continuous W-D cycles.

The baseline values for metal(loid)s in soils are known as a tool for the evaluation, prevention, and monitoring of the environmental quality of the soil. The main aim is to propose baseline values for metal(loid)s through the analysis of the concentrations in soils within natural areas; additionally, this study attempts to assess the environmental quality of soils in agricultural areas. The study was developed in the Piedemonte Llanero from Colombia a region with more than 5000 mm year−1 of pluviometry. A total of 90 soil samples were collected in agricultural and natural areas. Chemical analysis was conducted by acid digestion following the method EPA 3050B and determined the metal(loid)s (Al, As, Fe, Cd, Cr, Cu, Mg, Mn, Ni, Pb, and Zn) through ICP-OES. This is the first time that baseline values are proposed for a region in Colombia. The values proposed (expressed in mg kg−1) are Cd (0.3), As (2.8), Cu (9.9), Ni (10.2), Pb (11.3), Cr (21.1), Zn (28.2), Mn (83.8), Mg (348), Fe (22,775), and Al (28,975). These values are comparatively lower than those reported for other regions in Latin America and the rest of the world. Also, agricultural soils are not contaminated. The possible explanation is as a consequence of the intense washing caused by the intense rainfall of the place. The results also demonstrated that the soils in this region are not contaminated. Finally, these advances will allow public and private organizations to establish criteria for the environmental and sustainable management of soils, especially on agricultural activities. [ABSTRACT FROM AUTHOR]

Urea is the main nitrogen (N) fertilizer used in the wheat crop, but it is susceptible to volatilization losses. These losses can be reduced by urease inhibitors such as N-(n-butyl) thiophosphoric triamide (NBPT). This study evaluated wheat yield and N utilization efficiency (NUtE) of the cultivar BRS Gralha-Azul in response to N levels, to urea coated with different levels of NBPT, to the timings of N fertilization, and to environmental conditions experienced in-season in Brazilian Rhodic Oxisols. The experiment was carried out in three environments: Londrina under rainfed and irrigated conditions, and Ponta Grossa under rainfed conditions. Agronomic features related to N plant nutrition and wheat yield were assessed. Environmental conditions determined the effectiveness of N fertilization and NBPT on NUtE and grain yield. In Londrina, irrigation improved the density of fertile spikes and the N concentration and N accumulation in shoot dry matter, which contributed to increase grain yield by 39%. Nitrogen fertilization increased NUtE for shoot dry matter production in all the environments, and reduced NUtE for grain yield only in Londrina under rainfed conditions. NBPT is not effective under acid soil conditions combined with high water availability. Nitrogen fertilizer applied only at sowing may be enough for the spring wheat crop to achieve its yield capacity in subtropical environments. The management of N fertilization and NBPT can be improved if the historical data on environmental features throughout the wheat-growing season are considered. An alternative for increasing grain yield under drought conditions is to improve plant N uptake by increasing the N concentration in the soil solution via N fertilization. The optimal level of NBPT for coating urea depends on the N fertilizer level applied to wheat crop, as well as on the timing of N fertilization. Thus, the most suitable procedure for wheat farmers would be to customize the NBPT level according to their specific environmental conditions and N fertilization management practices, instead of purchasing N fertilizer with a single NBPT level. [ABSTRACT FROM AUTHOR]

Studying the electrochemical behavior of colloidal particles is important for fertility management and soil conservation, since it enables the understanding of several physicochemical phenomena that occur in soils. The objective of this study was to determine the point of zero charge (PZC) and the electrochemical behavior of surface and subsurface samples of three Red-Yellow Latosols (Oxisols), with different mineralogical and textural characteristics, through potentiometric titration and ionic adsorption. The point of zero charge (PZC) and the electrochemical behavior were determined in samples from the A and B horizons of three Red-Yellow Latosols: very clayey kaolinitic (LVAcr), very clayey gibbsitic (LVAgr) and sandy loam kaolinitic (LVAcm). The analyses were conducted in soil samples with particle size smaller than 0.7 mm, with desaturation of aluminum (Al3+), and smaller than 2 mm, without desaturation. Solutions containing sodium (Na+) and nitrate (NO3−) as indifferent electrolytes were used in all methods. The LVAgr, even with higher organic matter contents, had higher PZC, indicating the importance of mineralogical composition for this characteristic. Among the two kaolinitic soils, there was higher PZC in LVAcm, with lower organic matter content; however, both soils had higher PZC in the B horizon than in the A horizon. The net electrical charge estimated by the potentiometric titration method was equivalent to the net charge estimated by the ionic adsorption method for horizons A and B of LVAgr and LVAcm. At the same time, there was underestimation of the net negative charge by the potentiometric titration method for the A and B horizons of LVAcr. [ABSTRACT FROM AUTHOR]

Humid tropical forests on highly weathered soils are often characterized by low bioavailable phosphorus (P) concentrations. These ecosystems also often experience low and fluctuating redox conditions. Little is known about how soil redox conditions affect P availability and how this might feedback on biogeochemical cycling. Here we used soils from a wet tropical rainfall gradient in Puerto Rico to explore the effects of redox on P bioavailability and associated biogeochemical processes. Concentrations of soil carbon (C) and poorly crystalline iron (Fe) and aluminum (Al) minerals increased at least twofold with increasing rainfall, reflecting stronger anaerobic conditions at wetter sites and associated declines in decomposition. The fraction of the total P pool in the NaOH-extractable organic form also generally increased with increasing rainfall. In a laboratory incubation experiment using three sites along the gradient, P amendment increased aerobic CO2 production. However, anaerobic processes, including anaerobic respiration, Fe reduction, and methanogenesis, increased with P amendment at the driest site only. Microbial biomass C:P ratios decreased with P amendment under anoxic conditions at the driest site, an indicator of possible microbial P limitation at this site. Both microbial biomass C and P concentrations were lower under anoxic conditions than under oxic conditions across all soils, suggesting that anoxic conditions could be a more limiting factor to microbes than P concentrations. Overall, our results demonstrate that redox conditions regulate the extent of P limitation to biogeochemical processes in tropical forest soils. Phosphorus limitation was pronounced in aerated environments with low mean annual rainfall, whereas low redox conditions or associated factors under high rainfall conditions may have a stronger impact on biogeochemical cycling than P availability. [ABSTRACT FROM AUTHOR]

Soil is considered as one of the most important environmental factors for plant growth. However, the challenge is quantifying the sustainability of soil in agro-ecological systems. Presently, no soil quality assessment has been carried out in the island Mauritius or Small Island Developing States (SIDS) which would help to provide more scientific and precise advice to farmers for fertilisation and/or amendment of the soil. This is a particular handicap when recommendations need to be formulated to shift from conventional agricultural practices to a more sustainable and ecosystem-based approach. The present study attempted to determine the limiting factors of soil quality characterisation following different treatments comprising of mulch, no-mulch, N-based fertiliser, no fertiliser, tillage and no-tillage, and thereafter compare the differences in soil quality with conventional practices. In the present study, soil organic carbon (SOC), bulk density (BD), exchangeable potassium (Ex. K), exchangeable calcium (Ex. Ca), exchangeable magnesium (Ex. Mg), available phosphorous (Av. P), total nitrogen (Total N) and pH were selected as part of the Total Dataset (TDS) and the weighted additive Soil Quality Index (SQIw) of each of the eight treatments was calculated and compared. The study revealed that the SQIs ranged between 0.269 and 0.387 among all treatments, which suggest a low soil quality irrespective of the treatment. On a comparative basis, treatments no-till x mulch x fertiliser, no-till x no-mulch x fertiliser, and tillage x mulch x no-fertiliser are three options that can replace the conventional method tillage x no-mulch x fertiliser (control) based on the SQI. [ABSTRACT FROM AUTHOR]

Soil tillage is a high-cost operation in the replanting of sugarcane fields. Thus, measures to reduce this cost are desirable, provided that they promote good physical conditions for sugarcane development. The objective of this study was to evaluate the effect of chiseling in total area and in the planting row on the physical attributes of Oxisol and Ultisol after soil tillage and after sugarcane planting. The experimental design was in large and uniform plots, with two treatments and ten replicates. The Oxisol and Ultisol had clay contents of 590 and 168 g kg−1 in the 0.00–0.40 cm layer. Treatments consisted of soil tillage with chiseling in the planting row and with chiseling in total area. After soil chiseling and after planting, undisturbed soil samples were collected in each experimental plot, in three layers (0.00–0.10; 0.10–0.20 and 0.20–0.40 m) and at two sampling sites (row and interrow). In both soils, chiseling in total area was efficient to reduce soil density and increase macroporosity in sugarcane interrows, compared to chiseling in the row. The values of the physical attributes of the soils evaluated, in rows and interrows, were similar in the areas with chiseling in total area and row chiseling after sugarcane planting. Changes in Oxisol and Ultisol structure due to chiseling did not persist after sugarcane planting. The soil under row chiseling system has physical quality similar to that of the soil under total area chiseling system, regardless of texture. [ABSTRACT FROM AUTHOR]

Umbric ferralsols (UF) have organic carbon stocks within the first 1 m of soil profile depth that are nearly double the size (~19 kg C m−2) compared to the average carbon stocks of all other ferralsols (~10 kg C m−2). Here, we investigate processes that allow UF to gain and maintain such extraordinary carbon stocks. Using the International Soil Research and Information Center database, complemented with recently published datasets, we show that the carbon saturation capacity of the clay + silt fractions in UF (22.8 ± 5.7 g C kg−1 soil, n = 59) does not exceed the carbon saturation capacity in other ferralsols (23.3 ± 6.2 g C kg−1 soil, n = 165), thus eliminating a particularly retentive mineral matrix as a possible explanation. Rather, carbon stocks were correlated with the thickness of A horizons (106 ± 49 cm, n = 59 in umbric versus 35 ± 22 cm, n = 165 in non‐umbric ferralsols). We subsequently hypothesized that differences in A‐horizon thickness arose from two pedogenic scenarios: (i) superior carbon accrual resulting from a unique vegetation cover capable of allocating large quantities of carbon to belowground plant organs; and (ii) geomorphic processes that led to carbon burial. We evaluated the plausibility of these scenarios considering landscape history and associated carbon flux rates, hillslope position, as well as δ13C values and Ti/Zr ratios for subsets of ferralsol profiles studied by us in a region that encompasses latitudes from 26 to 7°S in eastern Brazil. We found that exceptional carbon stocks were most prevalent in the gradual transition zone (ecotone) between savanna and rainforest, likely resulting from erosion–deposition processes, historic changes of vegetation cover composed of grasses and arboreal elements, and active bioturbation. We suggest that attempts to sequester carbon in non‐umbric ferralsols will be most successful if they emulate or promote the biotic and abiotic processes prevalent in the savanna/rainforest ecotone. [ABSTRACT FROM AUTHOR]

ABSTRACT Sandy soil often has low nitrogen (N) stock. Thus, crops grown in sandy soil rely on high levels of N fertilization. The use of cover crops and efficient fertilizers can increase N stock in the soil and N availability in the topsoil, and reduce overall fertilizer costs. The objective of this study was to evaluate the effects of cover crops (fallow, a single grass species (ruzigrass), two grass species (ruzigrass + millet), one grass species (millet) with legumes [lime-yellow pea (2018) and velvet bean (2019)], and a mixture of three cover crops [two grass species (ruzigrass + millet) and one legume (lime-yellow pea (2018)] and velvet bean (2019), N sources (conventional urea and controlled-release urea) and N doses (70, 100 and 130 kg ha-1) on N dynamics in an Oxisol (Latossolo) with sandy texture in Brazil cultivated with cotton. Systems with the cover crops (average) had 17 % more total N stock in the soil than fallow systems. Inorganic N increased only in systems with legumes. The systems with cover crop mixtures had 70 % more ammonium than fallow systems. Systems only with grass species had low percentages of inorganic N in relation to total N in the soil. The increase in N-fertilizer rates augmented the N stock in the soil (total and inorganic). In the first year, controlled-release urea reduced the availability of inorganic N in cotton flowering, except for the system with mixed cover crops. After the cotton harvest, areas of controlled-release urea application had 12 % more inorganic N than the areas with conventional urea. Our findings show that the combined use of cover crops with high biomass production, moderate dose of N and controlled-release N can increase the availability of inorganic nitrogen in the upper layers of the soil in tropical areas with sandy soil and this can reduce nitrogen fertilizer consumption in the medium and long term in cotton fields.

The conversion from native forest to other land-use systems can decline the soil organic carbon (SOC) in tropical soils. However, conservationist management could mitigate SOC losses, promoting the functioning and stability of agricultural soils. This study aimed to address the influence of conversion from native forest to different land-use systems on SOC fractions in Northeastern Brazil. Topsoil soil samples were collected in areas under pasture (PAS), no-tillage (NT1 and NT2), eucalyptus (EUC), and native forests of Cerrado in Northeastern, Brazil. Total organic C, microbial biomass (MBC), particulate (POC), and mineral-occluded organic C (MOC), as well as fulvic acids (C-FA), humic acids (C-HA), and humin (C-HUM) fractions were accessed. The results showed that land conversion maintained similar levels of humic fractions and total organic carbon (TOC) stocks in the PAS, NT1, NT2, and EUC as compared to native Cerrado. Soils with the input of permanent and diverse fresh organic material, such as NT2, PAS, and EUC, presented high levels of MBC and POC, and the lowest C-FA:TOC and C-HA:TOC ratios. The land conversion to agricultural systems that include cropping rotations associated with pasture species such as Mombasa grass and eucalyptus prevents topsoil losses of active C compartments in the Cerrado of the Brazilian Northeast. It suggests that sustainable and conservationist management should be emphasized to maintain and improve the status of soil organic C.