Ap Horizon Research Articles

Comparative assessment of wetland and coastal plain soils in Calabar, Cross River State

The comparative assessment of wetland and coastal plain soils for agricultural productivity were studied. The investigation was carried out in two areas: Atimbo and Obufa Esuk in Calabar, Cross River State. The dominant particle size in bothcoastal and wetland soil was sandy texture. The mean bulk density values of 1.35 g/cm3 and 1.30 g/cm3 were obtained for Atimbo and Obufa Esuk coastal plain soil while 1.33 g/cm3 and 1.30 g/cm3 were obtained for Atimbo and Obufa Esuk wetland soil respectively. Total porosity in wetland soils was lower than coastal plain soil whereas moisture content in wetland soil was higher than coastal plain soil. Except Ap horizon in Atimbo coastal plain soil, the pH observed for the studied soils were all below pH of 5.0 unit which signifies high acidic condition. The mean organic carbon content in coastal plain soil was lower than wetland soil. Available phosphorus in the studied soils were high with Atimbo and Obufa Esuk coastal plain soil having a mean value of 32.10 and 32.42 mg/kg respectively, whereas those in Atimbo and Obufa Esuk wetland soils were 32.73 and 33.88 mg/kg respectively. The exchangeable calcium content obtained for both coastal and wetland soils were all below the critical limit of 5.0 cmolkg-1. Although exchangeable magnesium content was low in both soils but wetland soils was only slightly below the critical value of 1.5cmol/kg when compared to coastal plain soil. Both wetland and coastal plain soils were below (>0.2 cmolkg-1) critical level of K in soils of the zone. Also, exchangeable Na in both soil were low and below 0.3 cmol/kg limit and are adequate for cultivation of arable and tree crops. ECEC in both soils were low whereas percent base saturation was high. The mean C:N ratio in Atimbo and Obufa Esuk coastal plain soil were 11.45 and 15.48 respectively. Comparatively, the C:N ratio in Atimbo and Obufa Esuk wetland soils was slightly higher having a mean value of 16.39 and 18.14 respectively. This also reflect low rate of decomposition because of anaerobic condition of the soil. The Mg:K ratio were low in both soils. The Ca:Mg ratio values were high in wetland soil when compared with a normal range of 3:1-5:1 for productive soils and was low for coastal plain soil. Per cent silt content, moisture content, and exchangeable sodium of soil sample analyzed from wetland and coastal plain soil in Atimbo were significantly different (p<0.05). The result of the studied soils indicated that coastal plain soil is already losing its fertility status as typified by low values of organic carbon, total nitrogen, Exchangeable cations and high acidity couple with low moisture content; hence there is need to harnessed wetland soil for crop productivity. Wetland soils could be exploited for the cultivation of rice, oil palm, coconut, plantain, pineapple and sugar cane with judicious application of lime, and N and K fertilizers since these crops can perform well under acidic condition.Keywords: Wetland soil, coastal plain soil, soil fertility, soil properties

Microstructure of Soils of Different Geneses and Its Transformation in Constructozems of Moscow

The transformation of microstructure of constructozems was studied in a four-year-long (2012–2016) field experiment with the use of rheological and electron microscopy methods. Field studies were performed in the area of Moscow State University on three variants of artificial human-made soils (constructozems) differing in the structure of their profiles: (1) the control variant with the upper part composed of a homogenized Ap horizon, (2) the layered constructozem composed of a sequence of layers (Ap–peat–sand–Ap), and (3) the constructozem consisting of a mixture of the above-mentioned horizons. Electron microscopy attested to an increase in differentiation of the pore space in the upper Ap horizons in variants 1 and 2: new pores and chambers of different sizes appeared. In the loose porous mass of the peat layer in variant 2, more compact cohesive microstructures were formed. Microaggregation was identified in the upper layer of variant 3. Changes in the spatial arrangement of the solid phase of the soils were reflected in their rheological properties. A gradual increase in stability of structural bonds in the Ap horizon (variant 1) was detected. In variant 2, the underlying peat layer affected the shape of rheological curves in the Ap horizon. In variant 3, changes in strength properties of the mixed soil mass resulted in the formation of rheological behavior of fluid bodies typical of the plowed humus horizons.

Organic carbon pools and storage in the soil of olive groves of different age

SummaryCompared with annual crop cultivation, tree groves might represent a relevant land‐use system to improve C sequestration, but few data are available to support this hypothesis. To evaluate the potential of olive tree (Olea europaea L., 1753) cultivation to store soil organic C (SOC), we assessed (i) the distribution of organic C in active (water‐extractable and particulate organic C, WEOC and POC, respectively), intermediate (organic matter associated with stable sand‐size aggregates and silt‐ and clay‐size aggregates, SSAs and SCAs, respectively) and passive (organic matter resistant to oxidation, rSOM) pools, (ii) the phenol content of the C pools, (iii) the humic‐C distribution of the intermediate C pool and (iv) the stocks of SOC pools in two olive groves of different age (7 years (OG7) and 30 years (OG30)) compared with a nearby site with cereal crops (arable soil, AS). In OG30 the organic C stock of the olive grove was no different from that of the AS, but the distribution of SOC pools changed with the age of the olive groves. The WEOC and POC increased in the Ap horizon of OGs, probably because of the herbaceous cover and distribution of chipped prunings on the soil. There were fewer SSAs in OG7 than AS, possibly because of pedoturbations from deep tillage before the olive trees were established, but they increased in OG30. The increase in SSAs and SCAs in the Bw and BC horizons of OG30 was associated with humic‐C and unextractable‐C and a smaller phenol content than AS. This suggested that the olive tree roots had a positive role through rhizodeposition and root turnover, which favoured the stabilization of organic matter into aggregates at depth. In contrast to the active and intermediate C pools, the passive C pool did not vary following the change in land use from arable to olive grove.Highlights Effects of land‐use change from arable to olive grove on soil organic C pools and stocks. Soil organic C stock increased from 7‐ to 30‐year‐old olive orchard. Olive tree cultivation affected active and intermediate C pools, but not the passive C pool. After 30 years, the olive grove stored an amount of SOC similar to that of the arable system.

Potential of Wheat Straw, Spruce Sawdust, and Lignin as High Organic Carbon Soil Amendments to Improve Agricultural Nitrogen Retention Capacity: An Incubation Study.

Plants like winter wheat are known for their insufficient N uptake between sowing and the following growing season. Especially after N-rich crops like oilseed rape or field bean, nitrogen retention of the available soil N can be poor, and the risk of contamination of the hydrosphere with nitrate (NO3-) and the atmosphere with nitrous oxide (N2O) is high. Therefore, novel strategies are needed to preserve these unused N resources for subsequent agricultural production. High organic carbon soil amendments (HCA) like wheat straw promote microbial N immobilization by stimulating microbes to take up N from soil. In order to test the suitability of different HCA for immobilization of excess N, we conducted a laboratory incubation experiment with soil columns, each containing 8 kg of sandy loam of an agricultural Ap horizon. We created a scenario with high soil mineral N content by adding 150 kg NH4+-N ha-1 to soil that received either wheat straw, spruce sawdust or lignin at a rate of 4.5 t C ha-1, or no HCA as control. Wheat straw turned out to be suitable for fast immobilization of excess N in the form of microbial biomass N (up to 42 kg N ha-1), followed by sawdust. However, under the experimental conditions this effect weakened over a few weeks, finally ranging between 8 and 15 kg N ha-1 immobilized in microbial biomass in the spruce sawdust and wheat straw treatment, respectively. Pure lignin did not stimulate microbial N immobilization. We also revealed that N immobilization by the remaining straw and sawdust HCA material in the soil had a greater importance for storage of excess N (on average 24 kg N ha-1) than microbial N immobilization over the 4 months. N fertilization and HCA influenced the abundance of ammonia oxidizing bacteria and archaea as the key players for nitrification, as well as the abundance of denitrifiers. Soil with spruce sawdust emitted more N2O compared to soil with wheat straw, which in relation released more CO2, resulting in a comparable overall global warming potential. However, this was counterbalanced by advantages like N immobilization and mitigation of potential NO3- losses.

Modeling the effect of adsorption on the degradation rate of propiconazole in profiles of Polish Luvisols

Laboratory adsorption and degradation studies were carried out to determine the effect of time-dependent adsorption on propiconazole degradation rates in samples from three Polish Luvisols. Strong propiconazole adsorption (organic carbon normalized adsorption coefficients Koc in the range of 1217–7777 mL/g) was observed in batch experiments, with a typical biphasic mechanism with a fast initial step followed by the time-dependent step, which finished within 48 h in the majority of soils. The time-dependent step observed in incubation experiments was longer (duration from 5 to 23 d), and its contribution to total adsorption was from 20% to 34%. The half-lives obtained at 25 °C and 40% maximum water holding capacity of soil, were in the range of 34.7–112.9 d in the Ap horizon and in the range of 42.3–448.8 d for subsoils. The very strong correlations, between degradation rates in pore water and soil organic carbon and soil microbial activity, indicated that microbial degradation of propiconazole was most likely the only significant process responsible for the decay of this compound under aerobic conditions for the whole of the examined soil profiles. Modeling of the processes showed that only models coupling adsorption and degradation were able to correctly describe the experimental data. The analysis of the bioavailability factor values showed that degradation was not limited by the rate of propiconazole desorption from soil, but sorption affected the degradation rate by decreasing its availability for microorganisms.

Estimating Plant-Available Water in the Ap Horizon Using Geospatial Analysis of Field and SSURGO Data

ABSTRACTSoil provides many of the requirements needed for terrestrial plant growth, including an adequate supply of water. Because the proportion of plant roots is usually greatest in the top 10 to 15 cm of soil, the soil moisture content in the Ap horizon is particularly important for plant growth and crop yields. Uncertainties in estimates of plant available water in the Ap horizon (AWAp) often arise from variabilities in field, laboratory and geospatial data at a farm scale. The objectives of this study were to quantify and compare AWAp estimates across the 147-ha Cornell University Willsboro research farm using four different approaches: a) AWAp calculated from values reported in the SSURGO database for available water capacity (AWC) and Ap thickness for the soil map units (SMUs) present on the farm, b) AWAp estimated from soil texture data reported for the SSURGO SMUs, c) AWAp estimated from soil texture data determined from soil cores taken across the farm that were then averaged within each SMU, and d) spatially interpolating the AWAp values predicted from soil cores across the entire farm irrespective of SMU boundaries. Available water in the Ap horizon varied with soil order in the general trend of Alfisols > Inceptisols > Entisols regardless of the estimation approach used. Field measurement-based estimates of AWAp were lower, in general than the reported SSURGO values and estimates based on reported texture in the SSURGO database. The higher abundance of coarse fragments in the Ap horizon of the soil cores collected on the farm partially explains the lower field measurement-based AWAp estimates. In the SSURGO database, values reported for AWC are frequently obtained from a selected pedon from a “type location” and not from the actual study location. These “type locations” can be located far from study sites and even in different states. Although collecting detailed field data may not always be possible due to the high costs of field and laboratory measurements, it is important to understand the potential benefits and limitations of making field-scale and regional AW estimates using the SSURGO database.

Structural evidence for soil organic matter turnover following glucose addition and microbial controls over soil carbon change at different horizons of a Mollisol

Soil organic matter (SOM) in subsoils stores more than half of terrestrial organic carbon (C), and may sequestrate more C with increasing organic input due to its low C content (or high mineral reactivity) and high chemical stability. Organic inputs can stimulate microbial decomposition of native SOM (known as the priming effect), while being microbially decomposed and transformed into SOM. Yet, microbial controls over these processes and their influence on soil carbon change in soil profile remain elusive because of technical challenge to separate them. We overcame this challenge by employing a novel approach of combining 13C and 12C isotopes with quantitative solid-state 13C nuclear magnetic resonance (NMR). We used soil samples taken from three soil horizons in a Mollisol profile that dominated with fused-ring aromatics for a 43-day incubation. The signal intensities of the most dominant fused-ring aromatics and nonpolar alkyl groups were reduced due to the priming effect following the addition of 12C enriched glucose. Those signal intensities of O-alkyl and nonpolar alkyl groups increased in SOM spectra following the addition of 13C-labeld glucose, demonstrating accumulation of glucose and microbial residues. With the increasing glucose concentration, priming effect estimated using isotopic method and the magnitudes of signal loss estimated using 13C NMR both increased as exemplified for the Ap horizon soil. However, soil organic C content increased only when the added glucose concentration was beyond a previously non-quantified priming saturation threshold (between 36.0 and 100.0 g glucose-C kg−1 SOM-C). The increase of soil organic C was larger in the subsoils than in the topsoil due to lower microbial biomass, higher microbial growth efficiency (MGE) and mineral reactivity, which were related to the reduced priming effect and enhanced accumulation of microbial and glucose residues in the subsoils. The higher MGE in the subsoils agreed with stronger shifts of microbial community composition, characterized by phosphorous lipid fatty acid profiling, with changing glucose concentration during the incubation. Our findings highlighted the importance of priming saturation threshold, microbial mediation and mineral reactivity, but not SOM recalcitrance, in controlling the dynamics of SOM. Our study provided a novel approach to quantify these parameters and understand the controlling factors in relation to different plant types and soil types.

Role of rain intensity and soil colloids in the retention of surfactant-stabilized silver nanoparticles in soil

Undisturbed outdoor lysimeters containing arable loamy sand soil were used to examine the influence of either heavy rain events (high frequency of high rain intensity), steady rain (continuous rainfall of low rain intensity), and natural rainfall on the transport and retention of surfactant-stabilized silver nanoparticles (AgNP). In addition, the AgNP–soil associations within the Ap horizon were analyzed by means of particle-size fractionation, asymmetrical flow field-flow fractionation coupled with UV/Vis-detection and inductively coupled plasma mass spectrometer (AF4-UV/Vis-ICP-MS), and transmission electron microscopy coupled to an energy-dispersive X-ray (TEM-EDX) analyzer. The results showed that AgNP breakthrough for all rain events was less than 0.1% of the total AgNP mass applied, highlighting that nearly all AgNP were retained in the soil. Heavy rain treatment and natural rainfall revealed enhanced AgNP transport within the Ap horizon, which was attributed to the high pore water flow velocities and to the mobilization of AgNP–soil colloid associations. Particle-size fractionation of the soil revealed that AgNP were present in each size fraction and therefore indicated strong associations between AgNP and soil. In particular, water-dispersible colloids (WDC) in the size range of 0.45–0.1 μm were found to exhibit high potential for AgNP attachment. The AF4-UV/Vis-ICP-MS and TEM-EDX analyses of the WDC fraction confirmed that AgNP were persistent in soil and associated to soil colloids (mainly composed of Al, Fe, Si, and organic matter). These results confirm the particularly important role of soil colloids in the retention and remobilization of AgNP in soil. Furthermore, AF4-UV/Vis-ICP-MS results indicated the presence of single, homo-aggregated, and small AgNP probably due to dissolution.

GEMAS: CNS concentrations and C/N ratios in European agricultural soil

A reliable overview of measured concentrations of TC, TN and TS, TOC/TN ratios, and their regional distribution patterns in agricultural soil at the continental scale and based on measured data has been missing – despite much previous work on local and the European scales. Detection and mapping of natural (ambient) background element concentrations and variability in Europe was the focus of this work. While total C and S data had been presented in the GEMAS atlas already, this work delivers more precise (lower limit of determination) and fully quantitative data, and for the first time high-quality TN data. Samples were collected from the uppermost 20cm of ploughed soil (Ap horizon) at 2108 sites with an even sampling density of one site per 2500km2 for one individual land-use class (agricultural) across Europe (33 countries). Laboratory-independent quality control from sampling to analysis guaranteed very good data reliability and accuracy. Total carbon concentrations ranged from 0.37 to 46.3wt% (median: 2.20wt%) and TOC from 0.40 to 46.0wt% (median: 1.80wt%). Total nitrogen ranged from 0.018 to 2.64wt% (median: 0.169wt%) and TS from 0.008 to 9.74wt% (median: 0.034wt%), all with large variations in most countries. The TOC/TN ratios ranged from 1.8 to 252 (median: 10.1), with the largest variation in Spain and the smallest in some eastern European countries. Distinct and repetitive patterns emerge at the European scale, reflecting mostly geogenic and longer-term climatic influence responsible for the spatial distribution of TC, TN and TS. Different processes become visible at the continental scale when examining TC, TN and TS concentrations in agricultural soil Europe-wide. This facilitates large-scale land-use management and allows specific areas (subregional to local) to be identified that may require more detailed research.

Land use and soil legacy in the Lower Coastal Plain: A case study of Wormsloe State Historic Site, Georgia

Agriculture alters forest soil physical and chemical properties, often for decades to centuries, following agricultural cessation. Wormsloe State Historic Site, near Savannah, Georgia, has nearly a 300-year documented history of land use. To investigate agricultural soil legacies at Wormsloe, 120 random sample points were established across two land use history areas: Agriculture (some agricultural activity between 1736 and the present) and Reference (areas never farmed and under some forest cover from 1736 to present) within two mapped soil series (Chipley and Olustee). Landscape variables; profile characteristics; soil pH, carbon (C) and nitrogen (N) concentrations; extractable phosphorus (P), calcium (Ca), and magnesium (Mg) concentrations; and dominant vegetation were evaluated. An A horizon was always described in never farmed reference areas, and an Ap horizon was often, but not always, described in reforested agricultural areas. Soil P concentrations (Mehlich-1) were elevated (<i>p</i> = 0.05) in former agricultural areas. Soil pH (<i>p</i> = 0.04) differed across soil series but not land use. Discriminant analysis of sample plots reclassified by agricultural abandonment period (Reference/No Agricultural History, Civil War, Depression, and Modern) indicated that the Reference/No Agricultural History and Civil War period plots were similar and distinct from plots in areas abandoned during the Depression and Modern periods. Our ability to discriminate among dominant overstory and understory vegetation types using soil and site variables was relatively low.

Evaluation of fertilizers solubility and phosphate release in slightly acidic arable soil

ABSTRACTThe geochemical reactivity of single superphosphate (SSP), triple superphosphate (TSP), phosphate rock (PR), partially acidulated phosphate rock (PAPR) and potassium dihydrogen phosphate (KH2PO4) was evaluated in an incubation trial. The soil was Anthrosols, Ap horizon (Sandy loam). Solubility equilibrium of phosphates was calculated by phosphate (PPot = logH2PO4 – pH) and calcium (CaPot = logCa + 2pH) potentials. Next, activity ratio (AR°) and Woodruff potential (ΔF) were considered for estimating phosphate dynamics in the soil. Data showed that phosphate potentials stressed on significant solubility process and varied accordingly to the rates of the fertilizers: −5.50, −4.81, −4.47 and −4.09 for 0, 50, 100 and 150 kg P ha−1. The values of the Woodruff potential (ΔF) varied widely from −1929 to 8573 cal mol−1, i.e., from marginal supplying power in the case of the control treatment to very high supplying power for the TSP (Triple superphosphate). These findings are of practical value for the following reasons: TSP and KH2PO4 are recommended for quick and high P supply to plants; SSP and PAPR for moderate supply and finally PR for slow and low supply. Phosphorus efficiency should be treated with priority particularly for areas with intensive cropping and susceptibility to runoffs.

Fe-Mn nodules in a southern Indiana loess with a fragipan and their soil forming significance

Little is known about how Fe-Mn nodules vary in relation to pedogenetic horizons in soils derived from loess. In this investigation nodules were collected according to soil genetic horizons from a Fragiudalf in loess at Southeast Purdue Agricultural Center (SEPAC) in Indiana and physical, chemical, micro- and macromorphological features of nodules and their soil matrix were determined as a function of soil depth. The quantity, chemical composition, and micromorphology of the nodules varied with genetic horizons. The Ap horizon was found to contain the largest amount by weight of nodules (25.43g/kg) and this was likely due to soil erosion. After the Ap horizon, the 2Btx1 and 2Btx2 horizons had the greatest content of Fe-Mn nodules by weight. Nodules had lower concentrations of SiO2, Al2O3, K2O, TiO2, MgO, Na2O, and CaO; in contrast Fe2O3, MnO, and P2O5 in nodules showed clearly greater concentrations than that in the corresponding soil material. The SiO2 content decreased with nodule size whereas Fe2O3 and MnO increased. The least depletion of SiO2 in nodules of 1–2mm (N2) and 0.5–1mm (N1) was in the Bt2 horizon, and was greatest in the 2Btx2. The Al2O3 had accumulated in the N2 and N1 nodules within the Ap horizon and in the N2 within the 2Btx2 while other horizons were depleted of Al2O3. Brown nodules had a small Mn/Fe ratio (<1), whereas black nodules had a large Mn/Fe ratio (>1).The internal morphology of the nodules also varied with Mn/Fe ratios. The fungal hyphae or bacteria resulted in honeycomb, cell, cone, or dendritic structures. The cell and cone morphology required large Mn/Fe ratios, low pH, and high content of Ald. The scanning electron microscopy (SEM) analysis illustrated an elemental distribution trend such that the Mn was centralized in the nodule internal structure; whereas, Fe was concentrated towards the exterior. The band structure of nodules likely formed in response to seasonal wetting and drying as an accretionary process. Three basic formation stages for a well developed nodule can be inferred which correspond to different soil forming environments: 1) Fe enrichment for nucleus formation in wet soil, 2) Mn enrichment in an intense dry soil, and 3) Fe banding enrichment in a slightly dry soil. Nodule formation occurred synchronously with soil pedogenesis and can therefore be used as a proxy for understanding soil pedogenesis and the environment under which it occurred.

Use of the USDA National Cooperative Soil Survey Soil Characterization Data to Detect Soil Change: A Cautionary Tale

Core Ideas Long‐term databases are important for assessing soil change. The USDA Soil Survey Characterization Database provides long‐term soil data. Methods of analysis used have changed and soils were sampled only once. Changes in methods must be accounted for in soil change studies and trends. Recently, the USDA–NRCS National Cooperative Soil Survey Soil Characterization Database (NSCD) was reported to provide evidence that total nitrogen (TN) stocks of agricultural soils have increased across the Mississippi basin since 1985. Unfortunately, historical changes in methods used to measure TN were not fully accounted for in that report. We used NSCD archives to calibrate between wet (pre‐1995) and dry (post‐1995) digestion methods used in measuring TN and soil organic carbon (SOC), then evaluated temporal trends in SOC and TN stocks with data from 423 Alfisol and 900 Mollisol profiles representing the US Corn Belt. Data were grouped by moisture regime, farming history (presence of Ap horizon), and depth (0–20, 20–60, and 60–100 cm). Regressions showed geographic and textural influences on SOC, and that SOC increased with time among farmed soils, particularly at 20 to 60 cm. Soil TN was dependent on SOC, especially at the surface (R2 &gt; 0.71), and decreasing TN trends with time were found among farmed soils above 60‐cm depth. Increases in C to N ratios further suggested TN has been slowly stabilizing within soils of the US Corn Belt. However, C to N ratios &lt;9.0 were prevalent at 60–100 cm depth (&gt;60% frequency), indicating large TN stores remain in these soils. An increasing trend in SOC, TN, and C to N ratios among non‐farmed, aquic Mollisols suggested SOC and TN accumulations in wet soils typically located below croplands. Results suggest slow improvement in agricultural soils. However, resampling has not been broadly undertaken for NSCD soil profiles, hence use of this database to detect soil change should be approached cautiously.

Scales of Water Retention Dynamics Observed in Eroded Luvisols from an Arable Postglacial Soil Landscape

Core Ideas Hysteretic, seasonal, and interannual soil water retention dynamics were identified. Hydraulic functions for each drying and wetting event were described separately. Shorter term dynamics indicated soil structural and wettability changes. Longer term dynamics reflected soil management and erosion history. For each timescale, different processes control water retention dynamics. Soil water retention is frequently described by unique main drying curves measured in the laboratory on intact soil cores. In the field, however, soil pore structure changes as a result of swelling and shrinkage, wetting and drying, or tillage operations. For erosion‐affected arable soils characterized by truncated profiles, water retention dynamics could be even more complex. The objective of this study was to separate shorter term hysteretic from longer term seasonal dynamics in field‐measured water retention data of eroded Luvisols. Soil water content and matric potential data were from tensiometers and time‐domain reflectometry sensors of six lysimeter soil monoliths from two sites. For 2012 through 2014, drying and wetting periods were identified and fitted with the van Genuchten (VG) retention function. The results confirmed that drying water retention curves were steeper than those obtained in the laboratory. Steepness increased and fitted VG parameter values of saturated water content decreased within seasons, indicating that rewetting rates successively declined after each dry–wet cycle. Drying water retention curves returned to a similar level in each spring except for soils of transferred monoliths, where drying water retention tended to increase. Results suggested that water retention dynamics of eroded Luvisols was affected by continual incorporation of subsoil material in the Ap horizon and crop management practices in addition to hysteresis and seasonal dynamics. The disentangling of dry–wet cycles from time series of soil water content and matric potential was found useful for identifying the processes responsible for water retention dynamics and could eventually help improve flow and transport models.

Degradation rates of alachlor, atrazine and bentazone in the profiles of Polish Luvisols

AbstractThe degradation rates of three herbicides (alachlor, atrazine, and bentazone) were examined according to OECD Guideline 307 in three profiles of grey-brown podzolic soil (Luvisol) in a laboratory experiment. The aim of the experiment was to determine herbicide degradation parameters and their relationships with soil properties. Degradation processes were effectively described by a first-order model. However, in some cases, the best results were produced by bi-phasic kinetics (hockey-stick and bi-exponential model). The degradation rates of the tested herbicides at 25°C and 40% maximum water holding capacity, established based on half-life values in the Ap horizon, increased in the following order: atrazine (32.6-42.8 days) &lt; bentazone (3.4-16.6 days &lt; alachlor (4.4-5.7 days). The correlation analysis and the Principal Component Analysis revealed significant positive correlations between the herbicide degradation rates and the organic matter content of soils. The depth-dependent degradation factors obtained for topsoil and two subsoil horizons (1: 0.42: 0.11 – based on average values, and 1: 0.31: 0.12 – based on median values) reflect the degradation abilities of Polish Luvisols. The values noted are soil-specific; therefore, they can also be applied to other pesticides in Polish Luvisols.

Soil Organic Carbon Dynamics Responses to Soil Fertility in the Agricultural Regions of China

Increasing the soil organic carbon (SOC) content in croplands can not only improve the soil fertility, but also mitigate climate warming. To evaluate the extent of soil organic carbon density (SOCD) and SOC stock, the examination and prediction of the changes in SOC are essential. Using a field denitrification–decomposition model simulates the dynamics of SOC in the cultivated layer (Ap horizon, all soil depths of sites were 0–30 cm) across all croplands in China. The model simulations results showed that the SOCD and stock approach 3.69 ± 1.09 kg C m−2 and 4.73 ± 1.39 Pg C for the 128.2 M ha croplands in 2040, respectively. Interestingly enough, changes in SOC content (ΔSOC) and soil total nitrogen, soil available phosphorus, and soil available potassium showed negative correlations (P < 0.01), while soil pH value had positive (P < 0.01) correlation with ΔSOC in the cultivated layer. Excess fertilizer can be a disadvantage for SOC accumulation, Chinese croplands have relatively low SOCD and used good amount of fertilizer in comparison with the global average, but the croplands could have great potentials for soil carbon stock under better agricultural “watershed” management practices.

Response of copper concentrations and stable isotope ratios to artificial drainage in a French Retisol

Copper is a redox-sensitive trace element, which can be both, an essential micronutrient and a pollutant. We therefore analyzed Cu concentrations and stable isotope ratios (δ65Cu values) in a drained Retisol to trace the response of Cu to a changing hydrological regime and enhanced clay eluviation. The study soil was artificially drained 16years before sampling resulting in macroscopically visible pedogenetic changes and is thus a suitable site to investigate the influence of pedogenetic processes on the fate of Cu. Samples were collected from all horizons along a trench at four distances from the drain: 0.6m, 1.1m, 2.1m and 4.0m. In the E&Bt horizon, four different soil volumes (ochre, pale brown, white-grey and black) were sampled at all four distances from the drain. Furthermore, we analyzed soil solutions sampled with piezometer, porous cups, and at the drain outlet. The Cu concentrations were lowest in the surface (Ap) horizons (6.5–8.5μgg−1) and increased with depth to the clay-rich Bt horizons (10.5–12μgg−1), because of clay eluviation and associated Cu transport. The δ65Cu values significantly decreased from the surface (Ap=−0.25±0.07‰) to the deeper horizons, but showed no significant variation among the deeper horizons (−0.41±0.28‰) and no correlation with the clay content, indicating that clay eluviation did not significantly affect δ65Cu values. The isotopically heavier δ65Cu values in the Ap horizons can probably be explained by agricultural management practices like sludge application and fertilization. Close to the drain (position 0.6m), Cu concentrations were depleted and the lighter Cu isotope was enriched (−0.91±0.15‰) in the uppermost part of the E&Bt horizon. We attribute this to the changing redox conditions, caused by the lowering of the water level close to the drain. Copper concentrations in black and ochre volumes were significantly higher than in pale-brown and white-grey volumes. The black volume had significantly higher δ65Cu values than the ochre volume indicating preferential sorption/occlusion of the heavy Cu isotope by Fe oxides. Enhanced clay eluviation in bulk soil close to the drain and in specific soil volumes did not affect δ65Cu values. Cu concentrations (2.1–14μgL−1) and δ65Cu (0.04–0.42‰) values in water samples showed no clear relation with redox changes along the trench perpendicular to the drain. The enrichment of the heavy Cu isotope in the solution samples (Δ65Cu(soil-solution)=−0.61±0.41) indicates that reductive Cu mobilization is not the main driver of Cu leaching, because this would preferentially mobilize isotopically light Cu. We conclude that the eluviation of the <2μm fraction, strongly controlled Cu concentrations, but had no discernible effect on δ65Cu values. The changing redox conditions did not seem to control Cu concentrations and the stable isotope distribution in most of the bulk soil, soil volumes and soil water. Instead, weathering, complexation of leached Cu, Cu application with fertilizers and sorption processes within the soil controlled its δ65Cu values.

Climatic and Anthropogenic Impacts on Soil Formation

Soil succession directly records the information of environment and land use change, which is one of the important issues in global climate change research. In this paper, the authors investigated the soil samples and comparing their physical and chemical properties of soil diagnostic horizons. Results indicated that the Cum-ustic Isohumisols and Eum-Orthic Anthrosols had the same profile pattern, Ap-Bc-Bt/A-Bk-C. The characteristic temporal and spatial change of Ap horizon reflected several thousand years of dryland farming history in Weihe valley, but only several hundred years of dryland farming history on loess tableland.

GEMAS: Establishing geochemical background and threshold for 53 chemical elements in European agricultural soil

The GEMAS (geochemical mapping of agricultural soil) project collected 2108 Ap horizon soil samples from regularly ploughed fields in 33 European countries, covering 5.6 million km2. The <2 mm fraction of these samples was analysed for 53 elements by ICP-MS and ICP-AES, following a HNO3/HCl/H2O (modified aqua regia) digestion. Results are used here to establish the geochemical background variation and threshold values, derived statistically from the data set, in order to identify unusually high element concentrations for these elements in the Ap samples. Potentially toxic elements (PTEs), namely Ag, B, As, Ba, Bi, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, U, V and Zn, and emerging ‘high-tech’ critical elements (HTCEs), i.e., lanthanides (e.g., Ce, La), Be, Ga, Ge, In, Li and Tl, are of particular interest. For the latter, neither geochemical background nor threshold at the European scale has been established before. Large differences in the spatial distribution of many elements are observed between northern and southern Europe. It was thus necessary to establish three different sets of geochemical threshold values, one for the whole of Europe, a second for northern and a third for southern Europe. These values were then compared to existing soil guideline values for (eco)toxicological effects of these elements, as defined by various European authorities. The regional sample distribution with concentrations above the threshold values is studied, based on the GEMAS data set, following different methods of determination. Occasionally local contamination sources (e.g., cities, metal smelters, power plants, agriculture) can be identified. No indications could be detected at the continental scale for a significant impact of diffuse contamination on the regional distribution of element concentrations in the European agricultural soil samples. At this European scale, the variation in the natural background concentration of all investigated elements in the agricultural soil samples is much larger than any anthropogenic impact.

Decadal Nitrogen Fertilization Decreases Mineral‐Associated and Subsoil Carbon: A 32‐Year Study

AbstractCrop residues and manure are important sources of carbon (C) for soil organic matter (SOM) formation. Crop residue return increases by nitrogen (N) fertilization because of higher plant productivity, but this often results only in minor increases of SOM. In our study, we show how N fertilization and organic C additions affected SOM and its fractions within a 32‐year‐long field‐experiment at Puch, Germany. Five organic additions, no‐addition (control), manure, slurry, straw and straw + slurry, were combined with three mineral N fertilization rates (no, medium and high fertilization), which resulted in 1·17–4·86 Mg C‐input ha‐1 y‐1. Topsoil (0–25 cm) SOM content increased with N fertilization, mainly because of the C in free light fraction (f‐LF). In contrast, subsoil (25–60 cm) SOM decreased with N fertilization, probably because of roots' relocation in Ap horizon with N fertilization at the surface. Despite high inputs, straw contributed little to f‐LF but prevented C losses from the mineral‐associated SOM fraction (ρ &gt; 1·6 g cm‐3) with N fertilization, which was observed without straw addition. Above (straw) and belowground (roots) residues had opposite effects on SOM fractions. Root C retained longer in the light‐fractions and was responsible for SOM increase with N fertilization. Straw decomposed rapidly (from f‐LF) and fueled the mineral‐associated SOM fraction. We conclude that SOM content and composition depended not only on residue quantity, which can be managed by the additions and N fertilization, but also on the quality of organics. This should be considered for maintaining the SOM level, C sequestration, and soil fertility. Copyright © 2016 John Wiley &amp; Sons, Ltd.