Ap Horizon Research Articles

Young and century-old biochars strongly affect nutrient cycling in a temperate agroecosystem

Biochar as a soil amendment is often described as a promising agricultural practice for climate change mitigation and adaptation. However, while recent research showed limited effects of biochar in temperate regions, its long-term impacts on nutrient management in-situ have been overlooked. Here we studied charcoal residues from pre-industrial kiln sites as a proxy to determine the effects of century-old biochar (~200 years old) on nutrient cycles of 3 land covers in a conventionally cropped field. We compared nutrient cycles of soil containing either century-old biochar (CoBC), recently pyrolyzed biochar (YBC) produced from similar feedstock (oak) and amended in similar amounts and a reference charcoal free soil (REF). For these three modalities, we characterized soil chemical properties, the pore water nutrient concentration evolution with time and depth using suction cups, and the crop nutrient uptakes. Our results revealed soil pore water nutrient concentrations strongly depended on biochar age. Indeed, YBC resulted in lower N-NO3- and K+ leaching but higher P-PO4– pore water concentrations in the topsoil Ap (0–30 cm) horizon. In CoBC higher K+ and Mg2+ concentrations occurred in the pore water than in REF for subsoil horizon E (30–60 cm) and Bt (60–100 cm). Beyond soil pore water, CoBC also strongly increased soil total N, available K+ and Ca2+ but decreased available P contents compared to REF and YBC. Finally, although no change in crop productivity occurred, lower N, K, Ca and higher Mg plant uptakes were observed for modalities with biochar. This resulted in no difference in terms of nutrient exports from the field in chicory but it significantly decreased N, K, Ca exports from biochar rich soil under winter wheat in straw. This study delivers the first field-based evidence that the effects of hardwood biochar on nutrient cycles change over its lifetime in a temperate Luvisol soil, whereby young biochar impacts mainly pore water nutrient concentrations and aged biochar mainly plant available contents. In such a strongly managed environment, no differences are noted in productivity despite strong changes in the nutrient cycle. Our study provides insights for addressing long-term effects of biochar in cultivated lands not only in terms of agronomic perspectives but through a biogeochemistry lens.

The effect of resource-saving tillage technologies on the mobility, distribution and migration of trace elements in soil.

The influence of agricultural tillage technologies on the accumulation and distribution of trace elements in the soil is poorly studied. At the same time, intensive agriculture requires large amounts of fertilizers, growth stimulators, pesticides, and other substances, which can effect the ecological safety of the plant products and soil. This paper represents studying the effect of various agricultural techniques (including resource-saving technologies) on the mobility and profile distribution of Pb, Zn, and Cu in Haplic Chernozem. No significant influence of resource-saving tillage technologies was found on the total Pb content. Contrary, the resource-saving tillage technologies was observed to promote the growth of the total Zn and Cu content depending on the cultivation method (by 26% Zn, 34% Cu at minimal tillage, and 28% for both elements using No-till in Ap horizon). Amongst different applied agrotechnologies, there was no influence found on the profile distribution of total elements content. Only two horizons showed the total Pb content accumulation: biogenic (Ap-A) and carbonate (BC-C) horizon. In contrast, the only biogenic accumulation for Zn was determined. Copper characterizes by even distribution over the soil profile. The use of resource-saving agricultural technologies increases exchangeable fraction of Zn, Pb and Cu in soil almost by 1.5-2.0 times in the Ap horizon compared to moldboard ploughing. Despite the increase in the exchangeable fraction of Zn and Cu, this amount of micronutrients is not enough for adequate plant nutrition. The use of various agricultural technologies at Haplic Chernozem led to changes in the distribution of studied elements' exchangeable fraction over the soil profile. The study results suggested a need to increase the amount of Cu and Zn fertilizers applied to the soil with resource-saving cultivation technologies.

Chemical and mineralogical properties of Guanajibo clay (Plinthic Kandiudults)

A profile of Guanajibo clay (Plinthic Kandiudults) was evaluated to determine the ironstone content in the horizons and its chemical, physical and mineralogical properties. The mineralogy was characterized by X-ray diffraction (XRD) and the iron and aluminum oxide content determined by selective dissolution, using citrate-bicarbonate dithionite (CBD) and ammonium oxalate (OX) extractions. Soil color and the color of ground ironstone were determined with Munsell color charts. Soil texture, pH, and effective cation exchange capacity (ECEC) were also evaluated. The highest content of ironstone per unit mass was found in the Ap horizon (4.6%), decreasing in the Bt (0.9%) and Btv1 (1.0%) horizons. An increase in ironstone content was observed in the Btv2 horizon (3.8%), which suggests that this horizon was formed from alluvial deposits containing ironstone. No ironstone was found in the Btv3 horizon. The texture of the Ap horizon was a sandy clay, and the other horizons had a clay texture. Clay content reached a maximum value of 92.8% in the Btv3. The ECEC was low for the whole profile, ranging from 2.37 cmolc/kg in the Ap horizon to 4.37 cmolc/kg in the Btv3 horizon. The low ECEC is indicative of mineralogy dominated by highly weathered clay minerals like kaolinite and iron and aluminum oxides. The XRD analysis confirmed the presence of kaolinite, goethite, quartz, hematite and gibbsite in the clay fraction (< 2 mm) of the soil. A small peak corresponding to 2:1 clay minerals, probably Al-hydroxy interlayer vermiculite or montmorillonite, was observed in clay samples from the Ap, Bt and Btv1 horizons. The major mineral components of the ironstone were goethite, kaolinite and quartz. The fine earth fraction (150 µm) of the Btv1 horizon had a 2.8% CBD extractable iron content and a ratio of OX/CBD less than 0.10, meeting the two requirements established by Soil Taxonomy to qualify as plinthic. The other horizons met the requirement of OX/CBD ratios of less than 0.10, but had less than 2.5% iron extractable by the CBD method. Soil management practices that prevent soil erosion must be implemented in this soil to ward off exposure of plinthite to the surface and its irreversible hardening to ironstone.

Sustainability of the Soil Resource in Intensive Production with Organic Contributions

Organic agriculture is considered an alternative to sustainably preserve soil fertility. For 10 years, ongoing management with organic contributions was carried out in calcareous soil to support or increase fertility by applying 4 t ha−1 of solid poultry manure to produce organic Nopal Verdura (Opuntia Ficus-Indica). In addition, during the 2018 cycle, corn was established as an alternative to diversify agricultural production; the crop was monitored by measuring agronomic variables and the normalized differential vegetation index to evaluate the development of different doses of organic inputs with poultry manure, foliar applications with biofertilizers, or in the irrigation system. The soil physical and chemical analysis was carried out from 2015 to 2020 to monitor nitrogen, phosphorus, potassium, calcium, magnesium, and organic matter before planting and after harvest. The results indicated an increase in nitrogen (>50%), calcium (>130%), and magnesium (>20%), while there was a decrease in phosphorus (50%), potassium (60%), and organic matter (18%). The agronomic management caused an increment of EC in the horizon Ap until 12.93 dS m−1 at the end of each cycle due to the high ambient temperatures recorded and the inadequate irrigation water quality. We did not find significant differences (p > 0.05) in agronomic variables of corn with diverse contributions to organic. However, we obtained a maximum corn yield of 3.9 t ha−1 and nopal production of 143 t ha−1, despite problems of salinity in the horizons Ap during the agricultural cycle. Overall, processed poultry manure is a sustainable source of macroelements for the production of organic crops in calcisols; however, it is necessary to focus on and counteract potassium depletion and the increase in EC through appropriate agronomic management, with organic contributions, both solid and liquid, to increase or sustain production.

ПОДВИЖНОСТЬ И РАСПРЕДЕЛЕНИЕ ФОСФОРА В ЧЕРНОЗЕМЕ ОБЫКНОВЕННОМ ПРИ РАЗЛИЧНЫХ АГРОТЕХНОЛОГИЯХ

The study of the features of the content and profile distribution of total and available phosphates, depending on the applied agrotechnologies (traditional, minimal and No-till), was carried out. The object of the study was Haplic Chernozem carbonate of the southern zone of the Rostov region. The significant influence of the applied agricultural technology on the phosphate state of winter wheat agrocenoses was noted. The use of resource-saving technologies contributes to the accumulation of potential phosphate reserves in the upper horizons of the soil in comparison with the traditional technology with dump ploughing. The involvement of soil in agricultural production leads to an increase in the content of available phosphates (by 28-64 % in the Ap horizon, compared to virgin soil). The intensity of agricultural technology affects the mobility of phosphorus in the soil differently. In areas with dump ploughing, the maximum increase in the content of available phosphates was noted, both in comparison with the Chernozem of the virgin soil, and with the introduction of resource-saving agricultural technologies.

The effect of an extended agricultural reclamation on changes in physical properties of technosols in post-lignite-mining areas: A case study from central Europe

Opencast mining destroys soils that have formed over many thousands of years. Their place is taken by post-mining areas such as external and internal dumps with materials whose physical and chemical properties are unfavorable from the point of view of plant growth and development. In order to minimize the negative effects of opencast mining, reclamation is necessary. In this work, we examined the impact of 42-year agricultural reclamation, in which three variants of mineral fertilization (0NPK, 1NPK, and 2NPK) were applied in the cultivation of alfalfa with the addition of orchard grass on changes in physical properties of Technosols. After forty-two years of agricultural reclamation, there has clearly been a differentiation of post-mining material into genetic horizons that differ in physical properties. The surface part of Technosols was converted to a humus-enriched surface horizon (Ap), which consisted of two subhorizons: Ap1 and Ap2, differing in structure, color, and consistency. In the 1978–2020 period in Ap1 of fertilized soils, there was a decrease in bulk density (BD, 9.0–10.9%) and particle density (PD, 1.5%), but an increase in structural stability index (SI, 243–337%), soil porosity (SP, 15.5–19.2%), air-filled porosity (AFP, 10.8–11.7%), field capacity (FC, 49–21.6%), plant available water capacity (PAWC, 46.4–48.0%) and S-index (46.9–50%). In the Ap2 subhorizon, there was a similar trend of changes; however, BD (for 2NPK), FC (for 1NPK), and PAWC (for 1NPK and 2NPK) were not significant. BD (5.4–14.3%) increased in most horizons of parent material (Cd) between 1978 and 2020, and SP (10.9–29%), AFP (16. 2–73.9%), and S-index values (9.4–34.4%) decreased. On the other hand, PD, SI, FC, and PAWC values did not change significantly.Cultivation o alfalfa with orchard grass in the 1978–2020 period significantly affected the profile variation in physical properties of Technosols, which was not observed when the field experiment was set up (1978). In the Ap horizon, DB and PD had significantly lower values, while SI, SP, AFP, FC, PAWC, and S had significantly higher values compared to parent materials (Cd). This is related to the indirect effect of soil organic carbon (SOC), which was beneficial to improving the surface horizon properties of developing Technosols. The diversity of physical properties of the 42-years old post-mining Technosols in the Ap was dependent on fertilization, especially in the Ap1 subhorizon. In fertilized Technosols, the BD and PD values were lower, and SP, DP, AFP, FC, PAWC, and S values were higher compared to unfertilized Technosols. Parent material (Cd) horizons after 42 years of reclamation had similar physical properties regardless of fertilization.

Leaching Potential of Phosphite Fertilizer in Sandy Soils of the Southern Coastal Plain, USA

Novel biotechnology on transgenic plants capable of metabolizing phosphite (Phi), a reduced form of P, could improve the effectiveness of P fertilizers and reduce the P footprint in agriculture with the benefit of suppressing weed growth. However, potassium Phi (K-Phi) salts used as fertilizer are highly soluble in water. At the same time, sandy soils of the Southern Coastal Plain are vulnerable to leaching losses resulting from long-term Pi fertilizer application. We performed a replicated leaching trial using five soil materials that included three surface and two subsurface layers from cultivated topsoil (Ap horizon) with contrasting Phi and Pi sorption capacities. Each soil received three treatments K-Phi at rates 0 (control), 24, and 49 kg P ha−1 and leached twice with de-ionized water. All K-Phi-treated soils leached Phi except for the controls. A phosphorus saturation ratio (PSR) calculated from P, Al, and Fe in acid extracts indicated increasing environmental risk of Phi leaching in soils with lower Phi and Pi sorption capacities at rising rates of applied K-Phi. Because plants rapidly absorb Phi, further studies on the environmental impact of K-Phi fertilizer use should include the interaction of plants with soil properties and soil microbial activity at optimal Phi application rates for growing transgenic plants able to use Phi as a nutrient source.

Enzymatic Activity and Physicochemical Properties of Soil Profiles of Luvisols.

Most studies on soil enzymes are focused on the upper horizons of the soil profile, even though they transform the soil organic matter at every depth of the soil profile. The aim of this work was to investigate the distribution of β-glucosidase (GLU), nitrate reductase (NR), urease (UR), phosphatase (PHA), dehydrogenase (DHA) and catalase (CAT) activity through 14 trunked soil profiles of the Luvisols formed from a glacial till. The content of microbial biomass carbon (MBC) as well as physicochemical properties such as organic carbon (CORG), total nitrogen (NTOT), available P, K and Mg, soil density and porosity, pH in KCl and fractional composition were also studied. In general, enzymatic activity was highest in the top 30 cm layer of the profiles and decreased progressively towards the deeper horizons. The exceptions were the NR activity, which was active only in the Ap horizon and whose activity decreased sharply to nearly zero in the Bt horizon and parent rock, and the PHA activity, which was highly active even in the parent rock depth. The decreased availability of carbon and nutrients was the main driver of decreases in microbial abundance and enzymatic activity with depth. The enzymatic activity, when expressed on a CORG and MBC basis, behaves differently compared to the activity expressed on a soil mass basis. The activity decreased (NR), increased (PHA, UR), showed no clear pattern (GLU) or the changes were not significant (DHA, CAT). The content of CORG, NTOT, K and PAVAIL generally decreased with depth, while for Mg, there was no clear direction in the profile distribution. Future studies to characterize the substrate distribution within the soil profile and enzyme stability will provide further insight into the controls on nutrient cycling and related enzymes throughout the soil profiles.

Legacy of plaggen agriculture: High soil organic carbon stocks as result from high carbon input and volume increase

Plaggic Anthrosols are anthropogenic soils formed by former plaggen agriculture in north-western continental Europe. Here, we present an inventory of organic carbon (OC) concentrations and stocks of Plaggic Anthrosols and of reference soils in the vicinity without plaggen fertilization history from eight sites in northwest Germany (Lower Saxony, North Rhine-Westphalia) and the eastern parts of The Netherlands (North Brabant, Overijssel). To evaluate the enrichment of Plaggic Anthrosols with OC and the implications for OC stocks, soils were analysed for basic soil properties (bulk density, pH, OC − and nitrogen (N) concentrations), texture, and acid oxalate-(FeOX) and dithionite-citrate-bicarbonate-extractable iron (FeDCB) concentrations. Organic C stocks and plant-available water capacity (PAWC) were calculated. The plaggic topsoils are characterized by high OC concentrations (6.5–36.9 mg g−1) and a thickness of 53–124 cm, in contrast to the modern cultivated ∼30 cm thick topsoils of the reference soils with 10.6–24.0 mg g−1 OC concentration. The plaggen agriculture formed a soil with improved properties and conditions for plant growth. The addition of plaggen material to the topsoils induced a volume increase as well as higher OC concentrations in the Ap horizons, resulting in significantly higher OC stocks in the Plaggic Anthrosols (6.3–14.5 kg m−2) compared to the reference soils (4.9–10.5 kg m−2). The additional soil volume amounted to 30–56% to the total soil profile depth (1.0 to 1.6 m) and comprised 25–62% of the total OC stocks. Compared to the reference soils, the volume increase of the plaggic topsoil increased the PAWC in the effective rooting zone by 1.6 to 3.4 times. Plaggic Anthrosols represent a relic of historical farming with preserved high OC concentrations and improved storage capacity for plant-available water, causing higher nutrient availability and an increase in yields, which in turn result in higher in-situ OM input, additionally contributing to high OC stocks. The results of this study demonstrate the potential of soil melioration practices similar to the former plaggen management to induce high OC concentrations and increase OC stocks in sandy agricultural soils.

Potentialities and limitations of Planosols with distinct depths of diagnostic horizon

There is a variation in the depth of subsurface horizon of Planosols in semi-arid region, which may influence the agricultural potential and affect food production. The general aim of this study was to identify potentialities and limitations of two Planosols as a function of subsurface horizon depth. The adjacent profiles P1 and P2 were studied in Pentecoste (Ceará, Brazil). Morphological, physical, and chemical analyses were done aiming at soil characterization. Soil bulk density (BD), porosity, and penetration resistance (PR) were analyzed in a completely randomized split-plot design with four replicates to compare P1 and P2 and the horizons Ap and Btf. Btf was found at 62cm depth in P1 and at 18 cm depth in P2. Indicatives of water saturation were more evident in P2. The profile P1 showed lower hardness and higher friability, as well as higher acidity in subsurface (pHH2O from 4.4 to 4.7) and higher aluminum content (1.2cmolc kg-1). Both profiles were eutrophic and showed low contents of organic carbon (1.5 to 8.5g kg-1) and phosphorus (0.9 to 3.9mg kg-1). The sodium percentage in CEC was 9.1% in P1 and 5.5% in P2. Water retention increases in Btf compared with Ap was 7.3% in P2 and 2.7% in P1. Both profiles showed increase in BD in Btf, reaching 1.7g cm-3, while PR was higher in P2 (1.5 MPa). There are potentialities and limitations common to both soil profiles, but P1 has more physical potentialities and more chemical limitations than P2.

An Environmental Approach to Understanding the Expansion of Future Vineyards: Case Study of Soil Developed on Alluvial Sediments

The importance of soil properties in wine grape production is generally treated as secondary to climate and canopy management. This study was undertaken to characterize and classify a singular soil resource for a vineyard in a traditional viticultural region: Castilla-La Mancha, central Spain. The soil under study was described and sampled using standard soil survey procedures as outlined by FAO, and served as a pedologic window for Gleyic Fluvisol (Calcaric, Humic), according to the FAO System, or Fluventic Haploxerept, according to the Soil Taxonomy System. This soil, developed on alluvial materials of Holocene age related to the Gigüela river (either carbonatic or gypsiferous) has, in addition to obvious hydromorphic features (that reduce its use), high organic matter content (5.5% in the Ap horizon) and moderate salt content (between 1.14 and 2.39 dS/m). Other properties are common to most vineyard soils in Castilla-La Mancha, such as alkaline reactivity (pH between 7.6 and 8.2); calcium and magnesium as the dominant cations followed by sodium and potassium; finally, some deficiency in N (0.11%) and P (12.3 mg/kg). The most restricting soil factors for vineyard growth of this soil type were waterlogging, which can affect vine roots, and the appearance of certain salinity problems. The final conclusion of this study was that the use of the studied soil type for vineyard cultivation could be recommended to farmers only in the case of improving soil properties—for example, draining the river level.

Phosphorus adsorption characteristics in forested and managed podzolic soils

AbstractDespite the agricultural expansion into Canada's boreal ecoregion, little is known about the phosphorus (P) adsorption capacity in natural and managed Podzols' soil profiles. This information is critical for informing management decisions for P use efficiency and mitigating related environmental risks. Thus, this study aimed to evaluate P adsorption characteristics of podzolic horizons in natural and managed soil using nonlinear Langmuir and Freundlich adsorption models. A batch adsorption experiment was conducted using soils collected from distinct horizons of forested and managed fields in eastern and central Newfoundland, Canada. Nonlinear Langmuir and Freundlich fitted models had r values >.99 regardless of horizons, locations, and management history. The organic LFH, a surface horizon typical for forested Podzols, and a long‐term managed Ap horizon had the highest P retention capacities when compared to either newly converted soils or soils used as tree nursery following conversion from natural forest. A significant linear correlation and multiple regression models (p < .05) were established between P adsorption parameters and selected soil properties. Results suggest that following conversion from forest to agricultural use, long‐term management that includes tillage and lime and fertilizer application creates an Ap horizon with strong adsorption capacity, which could still fix P and serve as a source of P. The newly converted soils and the deeper soil horizons, for both natural and converted lands, do act mainly as P sinks; hence, crops may need larger quantities of P fertilizer increasing fertilizer expenses and also increasing future legacy P.

Earthworm burrow number and vertical distribution are affected by the crop sequence of a grass-clover rotation system

Grass-clover is an important element in crop rotations due to its beneficial agronomic properties including nitrogen build-up, stimulation of earthworms and their burrowing and maintenance of soil macropores. We studied the relationship between important elements of grass-clover management in a crop rotation and earthworm diversity and macropore depth distribution, diameter and density from the ploughing layer to a depth of 1 m. Treatments included winter rye, 1st year cutting + slurry, 3rd year cattle grazing + slurry, 3rd year cutting + slurry and 3rd year cutting without slurry. The four-species earthworm assemblages and their burrow spatial structure responded distinctly to the temporal sequence of farming system management elements. The relative density of the endo-anecic and epi-anecic earthworm species, Aporrectodea longa and Lumbricus herculeus, was higher in the grass-clover phase of the rotation than under the annual crop, and increased with the age of grass-clover. The same was true for Aporrectodea rosea, but density and biomass of Aporrectodea caliginosa showed the opposite trend. Cattle grazing favours the occurrence of burrows (>5 mm ⌀) made by the anecics, A. longa and L. herculeus, while otherwise decreasing the number of fine-medium macropores (<5 mm ⌀) below the topsoil. Our study reveals the intimate interdependence between the cropping sequence and the earthworm burrow structure with low number of detectable burrows under annual crops, then increasing in number during the grass-clover over 3 years. The highest number of burrows was found at 0.5 m depth in 3rd year cutting ± slurry, presumably because there is no soil disturbance by tillage in this horizon. The density of the endogeic A. caliginosa was negatively correlated with the presence of burrows and sensitive to grazing cattle compacting the topsoil. Positive correlations between burrows and density of L. herculeus indicate that this species was responsible for the burrows at one m depth while the density of A. longa was positively correlated with the burrows in the Ap horizon. We discuss the species composition in the grass-clover rotation system and its influence on soil ecosystem functioning.

Characterization of field-scale soil variation using a stepwise multi-sensor fusion approach and a cost-benefit analysis

The potential of a stepwise fusion of proximally sensed portable X-ray fluorescence (pXRF) spectra and electromagnetic induction (EMI) with remote Sentinel-2 bands and a digital elevation model (DEM) was investigated for predicting soil physicochemical properties in pedons and across a heterogeneous 80-ha crop field in Wisconsin, USA. We found that pXRF spectra with partial least squares regression (PLSR) models can predict sand, total nitrogen (TN), organic carbon (OC), silt contents, and clay with validation R2 of 0.81, 0.74, 0.73, 0.68, and 0.64 at the pedon scale but performed less well for soil pH (R2 = 0.51). A combination of EMI, Sentinel-2, and DEM data showed promise in mapping sand, silt contents, and TN at two depths and Ap horizon thickness and soil depth across the field. A clustering analysis using combinations of mapped soil properties or proximal and remote sensing data suggested that data fusion improved the characterization of field-scale variability of soil properties. The cost-benefit analysis showed that the most accurate management zones (MZs) for topsoil can be generated only using estimated soil property maps while it was the most costly as compared to other data sources. For an intermediate-high (for topsoil) and high (subsoil) accuracy and a moderate economic budget, the combination of sensors (proximal + remote sensing + DEM) might be a better approach for effective MZs generation than collecting soil samples for laboratory analysis while the latter produced the most accurate maps for topsoil. It can be concluded that pXRF spectra can be useful for predicting key soil properties (e.g., sand, TN, OC, silt, clay) at different soil depths, and a combination of proximal and remote sensing provides an effective way to delineate soil MZs that are useful for decision-making.

Spatial organization of soil microaggregates

The physical arrangement of compounds in soil microaggregates is controlling many ecosystem functions such as soil stability and C sequestration. However, little is known about the spatial arrangement of organic and inorganic compounds in soil microaggregates, due to the lack of in-situ analyses of undisturbed material. We hypothesized that microaggregates are spatially organized due to interactions between organic matter and mineral phases. To test this, we separated the water stable, occluded, large and small microaggregate fractions (250–53 and 53–20 µm, 60 J ml−1 dispersion energy) from Ap horizons of a toposequence of sandy to loamy Luvisols (Germany) with increasing clay contents (19 to 35% clay), and subjected in total 60 individual aggregates to elemental mapping by electron probe micro analysis (EPMA), which recorded C, N, P, Al, Fe, Ca, K, Cl, and Si contents at 1 × 1 µm resolution. Stoichiometric element ratios characteristic for organic and inorganic matter were used to define discrete components of the aggregates and analyze their spatial arrangement. We found a pronounced heterogeneity in content and arrangement of discrete aggregate components, which was not reproducible for different specimens from the same soil microaggregate fraction, and thus largely independent of clay content in soil. However, nearest neighbor analyses revealed close spatial correlations between plant detritus (C:N app. 100:10) and microbial organic matter (C:N app. 10:1) indicating a spatial relationship between source and consumer. There was no systematic relationship between soil minerals and organic matter, suggesting that well-established macroscale correlations between contents of pedogenic oxides and clay minerals with soil organic matter storage do not apply to soil microaggregates.

Shrink-swell soils of Palakkad district, Kerala: Their characteristics and classification

Representative pedons of Karuvapara series (P1) and Vannamada series (P2) from Palakkad district of Kerala were characterized and classified. The soils were very dark grayish brown to dark brown (P1) and very dark grayish brown to black (P2). The texture of the P1 varied from clay loam (Ap horizon) to clay and gravelly clay in sub-soils, while it was sandy clay (Ap horizon) to clay but sandy clay loam in last two horizons of P2. The pH of the soils in different horizon ranged from 7.1 to 8.2. Vannamada soils retained higher organic carbon (1.38% in Ap horizon) than Karuvapara soils. These soils had medium content of available N barring Ap horizon of P2 but high in available P (surface layer) and K. Available S, DTPA-Cu, DTPA-Fe, DTPA-Mn and hot water-soluble B in the soils were above the critical limit but DTPA-Zn was deficient except in Ap horizon of P2. These soils were classified as Typic Haplusterts (P1) and Vertic Epiaquepts (P2) at subgroup level.

Monitoring of the Contents of Manganese, Zinc, and Copper in Soils and Plants of the Central Chernozemic Region of Russia

The paper discusses the data obtained in 2015–2018 by the State agrochemical monitoring of soils in Belgorod oblast. The research revealed that organic fertilizers are the main source of microelements entering phytocenoses. They are responsible for 79.2% manganese, 87.3% zinc and 84.2% copper of their total amount introduced with fertilizers and ameliorants. The Ap horizon of the ordinary chernozem (Haplic Chernozem) in the steppe zone contains 1.15, 1.18, and 1.14 times more manganese, zinc, and copper, respectively, than the typical chernozem (Haplic Chernozem) in the forest—steppe zone. The studied microelements show the biophylic accumulation in the arable layer. The average total content of manganese, zinc, and copper in the Ap horizon was higher than that in CCa horizon in 1.49, 1.17, and 1.22 times, respectively, in the typical chernozem; and 1.42, 1.22, and 1.16 times in the ordinary chernozem, respectively. The results of continuous monitoring proved that 38.6; 98.7, and 98.2% of the studied arable soils manifest a low supply with manganese, zinc, and copper, respectively. The highest content of manganese was found in grain (1053 mg/kg) and straw (841 mg/kg) of white lupine; that of zinc (43.5 mg/kg), in the grain of the same crop; and the maximal amount of copper was found in the soybean grain (10.5 mg/kg). The lowest accumulation of manganese (9.22 mg/kg) and zinc (26.45 mg/kg) is typical for pea grains, and that of copper, for winter wheat grains (3.60 mg/kg). The concentration of microelements was higher in grains than in straw of winter wheat, soybean and white lupine; whereas the inverse relationship was found for pea plants.

Adsorption of bentazone in the profiles of mineral soils with low organic matter content.

The current laboratory adsorption study aimed at determination of the values of adsorption distribution coefficient (Kd) of bentazone in the profiles of Arenosols, Luvisols, and Cambisols, which are the most common arable mineral soils in Poland. The study attempted to identify the soil components that bind bentazone and the principal adsorption mechanisms of this compound as well as create a model capable of predicting its adsorption in soils. The Kd values determined in batch experiments after 24 h of shaking were very low, and ranged from 0.05 to 0.30 mL/g for the Ap horizon and 0 to 0.07 mL/g for subsoils. The results indicated that the anionic form of bentazone was adsorbed on organic matter, while in acidic soils the neutral form of bentazone was adsorbed on organic matter and sand. The detailed analyses of mineralogical composition revealed that the principal mineral that was responsible for the adsorption of bentazone was quartz, which content was strongly positively correlated with the sand fraction. In soils with pH < 5 and an organic carbon content of < 0.35%, quartz exhibited much greater affinity for the neutral bentazone form than organic matter. Fourier transform infrared photoacoustic spectroscopy analyses supported by computational methods have shown the most probable mechanisms behind the adsorption of bentazone on quartz. The created model, assuming the adsorption of bentazone on organic matter and on sand and using the spectrophotometrically determined dissociation constant of bentazone, very well explained the Kd variance in the 81 examined soils, while correctly predicting the adsorption based on soil properties described in the published data.

Soil organic carbon content: decreases partly attributed to dilution by increased depth of cultivation in southern Ontario

Soil organic carbon contents and depths of Ap horizons (i.e., cultivated topsoil) from Ontario soil survey reports were reviewed, analyzed, and compared from 1950 to 2019. Organic carbon concentrations have declined from 2.85% to 2.34% in Ap horizons, whereas depths have increased by 40%. Considering the entire Ap horizon depth, we show that soil carbon stocks (kg C·ha−1) may be constant or increasing. Losses of organic carbon due to cultivation should not be discounted; however, dilution of organic carbon within a deeper plow layer may contribute significantly to observed decreases in organic carbon concentrations in topsoil.

Genesis and classification of rice-maize-sorghum growing Vertisols in semi-arid tropical region of Chinnapalem village of Guntur district in Andhra Pradesh

The study was carried out in semi-arid tropical ecosystem of Chinnapalem Village of Guntur District. This study was an embodiment with an objective of genesis and classification of some black soils in semi-arid tropical region of Andhra Pradesh. The black soils of Chinnapalem Village, Duggirala mandal were formed at nearly level to plain topography with river alluvium parent material. All the pedons exhibited clear and smooth boundary in surface horizons and diffuse and wavy boundary in the sub-surface horizons and A horizon was designated as Ap horizon while B horizon was Bss due to the presence of well-formed distinct slickensides. The soil colour varied from from very dark gray to black. Textural class of fine earth was clayey with medium to coarse, moderate to strong and angular to subangular blocky in structure. The consistence varied from very hard to extremely hard, firm to extremly firm and sticky to very-sticky and plastic to very-plastic in dry, moist and wet conditions, respectively. Due to the presence of vertic features like slickensides, pressure faces, cracks and presence of more than 30 % clay in all the horizons were grouped under Vertisols and classified as Typic Haplusterts and ideal for cultivation of rice, sorghum, and maize.