A study of the effects of land use changes on soil physical properties and organic matter

Changes in land use can significantly affect soil properties. This study was conducted in the Taleghan watershed of Tehran Province, Iran, to determine the effects of land use changes on soil organic matter (SOM) and soil physical properties including soil aggregate stability, saturated hydraulic conductivity, infiltration rate, available water content, total porosity and bulk density (BD). In the present study, two sites contained adjacent land uses of natural pasture and dryland farming were selected. Soil samples were taken from depths of 0–15 and 15–30 cm for each land use. The results indicated that the conversion of natural pasture to dryland farming led to a significant decrease in SOM at 0–30 cm in the first and second sites (24.7 and 44.2%, respectively). In addition, a significant increase in BD was observed at a depth of 0–30 cm in dryland farm soils (1.39 g cm^–3) compared to pastureland (1.20 g cm^–3) at the first site. An increase in BD was also observed at the same depth of dryland farm soils (1.46 g cm^–3) and pastureland soils (1.42 g cm^–3) at the second site. In addition, total porosity, mean‐weight diameter of aggregates, saturated hydraulic conductivity, available water content and estimated final infiltration rate showed significant differences between land uses. The results showed that the conversion of natural pasture to dryland farming alters soil properties that negatively affect soil productivity and erodibility. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of charcoal production on maize yield,chemical properties and texture of soil

The effects of charcoal production on soil textural and chemical properties were investigated in Ejura, Ghana. The aim was to study the effects of heating and charcoal residue on maize yield, soil texture and soil chemical properties. Composite samples were taken from the 0–10 cm layer of soil at charcoal-making sites and from adjacent fields (control). Twelve sites were randomly selected for the study across the range of the Kotokosu watershed. Maize was planted in four selected locations on charcoal site soils (CSS) and adjacent field soils (AFS) to assess the impact of charcoal production on crop yield. There was a significant increase in soil pH, base saturation, electrical conductivity, exchangeable Ca, Mg, K, Na and available P in the soil at the kiln sites as compared to the adjacent soils. A relative change of up to 329% was observed in K while organic C and total N decreased by 9.8% and 12.8%, respectively. Organic C and total N were highly correlated ( P <0.01) and both parameters significantly ( P <0.05) depended on clay minerals in the soils. Soil texture was also modified with a significantly higher sand content and lower clay fraction in the CSS. The grain and biomass yield of maize increased by 91% and 44%, respectively, on CSS as compared to AFS. Further research to ascertain the long-term effects of charcoal production on the soil environment and the fertility of tropical soils is needed.     

Effects of Clear‐Cutting Alder Coppice on Surface Soil Properties and Aboveground Herbaceous Plant Biomass

The purpose of this investigation was to evaluate the effects of clear‐cutting and skidding impacts on surface soils in an alder coppice and aboveground herbaceous biomass. For this purpose, experimental sites used in the study were a randomized complete block with four replications. Some soil properties were measured at 60 pits at 0 to 5 cm and 5 to 10 cm deep in control, normal harvest, and main skid trail sites. In the main skid trail site, as compared to the control and normal harvest site, the bulk density increased from 0.90 to 1.52g cm^?3, the soil organic‐matter content decreased from 4.77% to 1.65%, and saturated hydraulic conductivity decreased from 86.34 to 9.6 cm h^?1 at 0 to 5 cm deep. Optimization of harvesting time and rehabilitation of skid roads needed to be done to prevent and minimize negative impacts of the skid roads on soils.     

Simulated rainfall evaluation of revegetation/mulch erosion control in the Lake Tahoe basin: 2. Bare soil assessment

Slopes that have been disturbed through roadway, ski slope or other construction often produce more sediment than less disturbed sites. Reduction or elimination of sediment loading from such disturbed slopes to adjacent streams is critical in the Lake Tahoe basin. Here, use of a portable rainfall simulator (RS), described in the first paper of this series, is used to evaluate slope effects on erosion from bare volcanic and granitic soils (road cut and ski run sites) common in the basin in order to establish a basis upon which revegetation treatment comparisons can be made. Rainfall simulations (60 mm h⁻¹, approximating a 100‐year, 15‐minute storm) at each site included multiple replications of bare soil plots as well as some adjacent ‘native’, or relatively undisturbed soils below trees where available. Field measurements of time to runoff, infiltration, runoff, sediment discharge rates, and average sediment concentration were obtained. Laboratory measurements of particle‐size distributions using sieve and laser counting methods indicated that the granitic soils had larger grain sizes than the volcanic soils and that road cut soils of either type also had larger grain sizes than their ski run counterparts. Particle‐size‐distribution‐based estimates of saturated hydraulic conductivity were 5–10 times greater than RS‐determined steady infiltration rates. RS‐measured infiltration rates were similar, ranging from 33–50 mm h⁻¹ for disturbed volcanic soils and 33–60 mm h⁻¹ for disturbed granitic soils. RS‐measured runoff rates and sediment yields from the bare soils were significantly correlated with plot slope with the exception of volcanic road cuts due to the narrow range of road cut slopes encountered. Sediment yields from bare granitic soils at slopes of 28 to 78 per cent ranged from ∼1 to 12 g m⁻² mm⁻¹, respectively, while from bare volcanic soils at slopes of 22 to 61 per cent they ranged from ∼3 to 31 g m⁻² mm⁻¹, respectively. Surface roughness did not correlate with runoff or erosion parameters, perhaps also as a result of a relatively narrow range of roughness values. The volcanic ski run soils and both types of road cut soils exhibited nearly an order of magnitude greater sediment yield than that from the corresponding native, relatively undisturbed, sites. Similarly, the granitic ski run soils produced nearly four‐times greater sediment concentration than the undisturbed areas. A possible goal of restoration/erosion control efforts could be recreation of ‘native’‐like soil conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

Tillage Effects on Crop Yield and Physicochemical Properties of Sodic Soils

Tillage modifies soil structure and has been suggested as a practice to improve physical, hydrological and chemical properties of compacted soils. But little is known about effect of long‐term tillage on physicochemical soil properties and crop yield on sodic soils in India. Our objective was to investigate the effect of different tillage regimes on crop yield (wheat and paddy rice) and physicochemical properties of sodic soils. Two sodic sites under conventional tillage for 5 (5‐YT; 5‐year tillage) and 9 (9‐YT; 9‐year tillage) years were selected for this study. Changes in crop yield and physicochemical soil properties were compared with a control, sodic land without any till history, that is, 0‐year tillage/untilled (0‐YT). Five replicated samples at 0‐ to 10‐cm and 10‐ to 20‐cm soils depths were analysed from each site. In the top, 0‐ to 10‐cm soil depth 5‐YT and 9‐YT sites had higher particle density (Pd), porosity, water holding capacity, hydraulic conductivity, organic carbon, total nitrogen (N_t), available nitrogen (N_avail), phosphorus (P_avail) and exchangeable calcium (Exch. Ca⁺⁺) than 0‐YT, whereas bulk density (Bd), C : N ratio and CaCO₃ were significantly lower. Bd, pH, EC and CaCO₃ increased significantly with depth in all the lands, whereas Pd, porosity, water holding capacity, hydraulic conductivity, organic carbon, N_t, N_avail, P_avail and Exch. Ca⁺⁺ decreased. We conclude that continuous tillage and cropping can be useful for physical and chemical restoration of sodic soils. Copyright © 2014 John Wiley & Sons, Ltd.     

黄土丘陵区典型植被土壤物理性质差异及其对导水特性影响

选取黄土丘陵区12种典型植被样地,通过测定各样地不同土层植物残体生物量、土壤容重、毛管孔隙度、非毛管孔隙度及饱和导水率,研究各指标随土层深度和植被类型的变化规律及其对土壤饱和导水率的影响。结果表明:(1)除容重随土层深度增加外,植物残体、毛管孔隙度、非毛管孔隙度和饱和导水率均随土层深度减少,其中植物残体大多集中于表层土壤(0—10 cm),占总残体生物量的51.4%～85.7%。(2)不同植被类型其植物残体及土壤物理性质存在显著差异,乔木林地植物残体、农耕地土壤容重、灌木林地非毛管孔隙度及饱和导水率均最大,而毛管孔隙度与不同土地利用类型间无显著差异。(3)饱和导水率随植物残体生物量密度(0—10 cm)和土壤容重呈幂函数减小,随毛管孔隙度和非毛管孔隙度呈幂函数增大;土壤容重(BD)和非毛管孔隙度(NCP)是影响土壤饱和导水率(K_s)的主要因素,且土壤饱和导水率可表示为两者的综合非线性方程(K_s=0.6BD~(-4.717)NCP~(0.203),P0.01,R~2=0.63,NSE=0.50)。此外,沙棘灌木林地平均饱和导水率最大,有利于降雨过程中土壤水分入渗,具有较强的水土保持功能。本研究结果可为黄土高原植被恢复生态水文效益评价提供理论依据。     

Improvement of degraded physical attributes of a saline-sodic soil as influenced by phytoremediation and soil conditioners

This study aimed to evaluate the use of phytoremediation and soil conditioners in the recovery of physical attributes of a saline-sodic Fluvic Neossol in Brazil Northeast. The applied treatments were: Atriplex nummularia L., as phytoremediation plant, due to its ability to extract salts from the soil; organic conditioners, such as bovine and sheep manure; gypsum and polymer, as chemical conditioners. Samples with preserved structure were collected at the time of the experiment installation and 18 months after in the layers 0–10 cm and 10–30 cm. The analyzed attributes were: water dispersed clay, dispersion index, bulk density, penetration resistance, soil porosity, and saturated hydraulic conductivity. The use of sheep manure, gypsum and polymer promoted an increase in saturated hydraulic conductivity in the 0–10 cm layer from 4.51 to 16.37 cm day^?1, 11.26 to 23.95 cm day^?1 and 7.24 to 22.77 cm day^?1, respectively. Gypsum increased the macroporosity in the superficial layer by 42.6%. Atriplex and polymer were more efficient at reducing soil penetration resistance. The polymer was more efficient at improving the physical properties. However, it is necessary to consider phytoremediation with Atriplex as a more sustainable alternative that can still be used as complementary fodder in animal feed.     

The Effects of Long‐term Fertiliser Applications on Soil Organic Carbon and Hydraulic Properties of a Loess Soil in China

Based on a 28‐year in situ experiment, this paper investigated the impacts of organic and inorganic fertiliser applications on soil organic carbon (SOC) content and soil hydraulic properties of the silt loam (Eumorthic Anthrosols) soils derived from loess soil in the Guanzhong Plain of China. There were two crop (winter wheat and summer maize) rotations with conventional tillage. The treatments included control without fertiliser application, organic manure application (M), chemical fertiliser application (NP), and the application of organic manure with chemical fertiliser (MNP). The results showed that the 28‐year organic manure applications (M and MNP) significantly (p < 0·05) increased SOC content at surface layer (0–10 cm), but the effect of chemical fertilisers alone on SOC was not significant. Organic manure treatments (M and MNP) apparently improved soil hydraulic properties. Compared with control, field capacity and total porosity significantly (p < 0·05) increased while soil bulk density significantly (p < 0·05) decreased for organic manure applications. The M and MNP treatments increased soil water retentions by 3·2–10·8%, which was dependent of suction tensions. However, the NP treatment had no significantly impact on soil water retention compared with control. Neither organic nor inorganic fertiliser applications significantly changed saturated hydraulic conductivity. However, a clear difference was observed for unsaturated hydraulic conductivity between the M and the control at 0–5 cm. Overall, long‐term applications of organic manuring increased SOC content and amended soil hydraulic properties. However, the effects of chemical fertilisers on these soil properties were limited. Copyright © 2015 John Wiley & Sons, Ltd.     

Soil microbial biomass and activity: the effect of site characteristics in humid temperate forest ecosystems

Microbial biomass, respiratory activity, and in‐situ substrate decomposition were studied in soils from humid temperate forest ecosystems in SW Germany. The sites cover a wide range of abiotic soil and climatic properties. Microbial biomass and respiration were related to both soil dry mass in individual horizons and to the soil volume in the top 25 cm. Soil microbial properties covered the following ranges: soil microbial biomass: 20 µg C g^–1–8.3 mg C g^–1 and 14–249 g C m^–2, respectively; microbial C–to–total organic C ratio: 0.1%–3.6%; soil respiration: 109–963 mg CO₂‐C m^–2 h^–1; metabolic quotient (qCO₂): 1.4–14.7 mg C (g C_mic)^–1 h^–1; daily in‐situ substrate decomposition rate: 0.17%–2.3%. The main abiotic properties affecting concentrations of microbial biomass differed between forest‐floor/organic horizons and mineral horizons. Whereas microbial biomass decreased with increasing soil moisture and altitude in the forest‐floor/organic horizons, it increased with increasing N_tot content and pH value in the mineral horizons. Quantities of microbial biomass in forest soils appear to be mainly controlled by the quality of the soil organic matter (SOM), i.e., by its C : N ratio, the quantity of N_tot, the soil pH, and also showed an optimum relationship with increasing soil moisture conditions. The ratio of C_mic to C_org was a good indicator of SOM quality. The quality of the SOM (C : N ratio) and soil pH appear to be crucial for the incorporation of C into microbial tissue. The data and functional relations between microbial and abiotic variables from this study provide the basis for a valuation scheme for the function of soils to serve as a habitat for microorganisms.     

Vertical distribution of charcoal in a sandy soil: evidence from DRIFT spectra and field emission scanning electron microscopy

This study uses diffuse reflectance infrared Fourier Transform (DRIFT) spectrometry and field emission scanning electron microscopy to investigate the vertical distribution of charcoal in a sandy soil from SE Australia. The soil was sampled to bedrock (120 cm) at varying depths and bulk samples were fractionated into three particle‐sizes: macro‐ (2000–200 µm), micro‐ (200–60 µm) and mineral‐associated organic matter (MAOM, < 60 µm). Charcoal was isolated from 0–30 and 30–60‐cm depths. Soil charcoal was detected by using a DRIFT band centred at 1590 cm^?1 and scanning electron microscopy combined with energy dispersive spectroscopy. Charcoal content as a proportion of soil organic carbon (SOC) was estimated with linear regressions of cumulative DRIFT bands. At 0–30 cm, charcoal content as a portion of SOC did not differ significantly between particle‐size fractions, constituting 5–26% of SOC. At a depth of 30–60 cm, charcoal constituted 19–39% of SOC in the fractions. At 60–100 cm, charcoal was only detectable in the mid‐sized fraction, where it constituted about 17% of SOC. These results support our previous hypothesis of charcoal enrichment in the micro‐fraction inducing a greater SOC stability in this fraction as inferred from radiocarbon ages (Hobley et al., 2013). Our findings indicate that DRIFT spectra can be used to detect the presence and amount of charcoal in soil, which may prove to be a simple and low‐cost alternative to more laborious and costly detection methods.     

Effects of compaction on soil hydraulic properties,penetration resistance and water flow patterns at the soil profile scale

The aim of this study was to quantify the effects of compaction on water flow patterns at the soil profile scale. Control and trafficked plots were established in field trials at two sites. The trafficked treatment was created by four passes track‐by‐track with a three‐axle dumper with a maximum wheel load of 5.8 Mg. One year later, dye‐tracing experiments were performed and several soil mechanical, physical and hydraulic properties were measured to help explain the dye patterns. Penetration resistance was measured to 50 cm depth, with saturated hydraulic conductivity (K_s), bulk density, and macroporosity and mesoporosity being measured on undisturbed soil cores sampled from three depths (10, 30 and 50 cm). Significant effects of the traffic treatment on the structural pore space were found at 30 cm depth for large mesopores (0.3–0.06 mm diameter), but not small mesopores (0.06–0.03 mm) or macroporosity (pores > 0.3 mm). At one of the sites, ponding was observed during the dye‐tracing experiments, especially in the trafficked plots, because of the presence of a compacted layer at plough depth characterized by a larger bulk density and smaller structural porosity and K_s values. Ponding did not induce any preferential transport of the dye solution into the subsoil at this site. In contrast, despite the presence of a compacted layer at 25–30 cm depth, a better developed structural porosity in the subsoil was noted at the other site which allowed preferential flow to reach to at least 1 m depth in both treatments.     

Anisotropy of pore functions in structured Stagnic Luvisols in the Weichselian moraine region in N Germany

In order to determine if soil hydraulic properties present a direction‐dependent behavior, undisturbed samples were collected at different horizons and orientations (vertical, diagonal [45°], and horizontal) in structured soils in the Weichselian moraine region in northern Germany. The water‐retention curve (WRC), the saturated hydraulic conductivity (k_f), and the air permeability (k_a) were measured. The air‐filled porosity (?_a) was determined, and pore‐continuity indices (k_a/?_a, k_a/?_a², N) and blocked porosities (?_b) were derived from the relationship between k_a and ?_a. The development of soil structures with defined forms and dimensions (e.g., platy by soil compaction or prismatic up to subangular‐blocky by swelling–shrinkage processes) and the presence of biopores can induce a direction‐dependent behavior of pore functions. Although the pore volume as a scalar is isotropic, the saturated hydraulic conductivity and air permeability (as a function of air‐filled porosity) can be anisotropic. This behavior was observed in pore‐continuity indices showing that the identification of soil structure can be used as a first parameter to estimate if hydraulic properties present a direction‐dependent behavior at the scale of the soil horizon.     

Variability of CO2 and N2O emissions during freeze‐thaw cycles: results of model experiments on undisturbed forest‐soil cores

The amounts of N₂O released in periods of alternate freezing and thawing depend on site and freezing conditions, and contribute considerably to the annual N₂O emissions. However, quantitative information on the N₂O emission level of forest soils in freeze‐thaw cycles is scarce, especially with regard to the direct and indirect effect of tree species and the duration of freezing. Our objectives were (i) to quantify the CO₂ and N₂O emissions of three soils under beech which differed in their texture, C and N contents, and humus types in freeze‐thaw cycles, and (ii) to study the effects of the tree species (beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.)) for silty soils from two adjacent sites and the duration of freezing (three and eleven days) on the emissions. Soils were adjusted to a matric potential of –0.5 kPa, and emissions were measured in 3‐hr intervals for 33 days. CO₂ emissions of all soils were similar in the two freeze‐thaw cycles, and followed the temperature course. In contrast, the N₂O emissions during thawing differed considerably. Large N₂O emissions were found on the loamy soil under beech (Loam‐beech) with a maximum N₂O emission of 1200 μg N m^–2 h^–1 and a cumulative emission of 0.15 g N m^–2 in the two thawing periods. However, the sandy soil under beech (Sand‐beech) emitted only 1 mg N₂O‐N m^–2 in the two thawing periods probably because of a low water‐filled pore space of 44 %. The N₂O emissions of the silty soil under beech (Silt‐beech) were small (9 mg N m^–2 in the two thawing periods) with a maximum emission of 150 μg N m^–2 h^–1 while insignificant N₂O emissions were found on the silty soil under spruce (0.2 mg N m^–2 in the two thawing periods). The cumulative N₂O emissions of the short freeze‐thaw cycles were 17 % (Sand‐beech) or 22 % (Loam‐beech, Silt‐beech) less than those of the long freeze‐thaw cycles, but the differences between the emissions of the two periods were not significant (P ≤ 0.05). The results of the study show that the amounts of N₂O emitted in freeze‐thaw cycles vary markedly among different forest soils and that the tree species influence the N₂O thawing emissions in forests considerably due to direct and indirect impacts on soil physical and chemical properties, soil structure, and properties of the humus layer.     

Soil characteristics in teak plantations and natural forests in Ashanti Region,Ghana

Abstract

The goal of this study to was compare soils of natural forests converted to teak (Tectona grandis Linn. F) plantations (21.3±5.1 years) in the Offinso and Juaso Forest Districts in the Ashanti region, Ghana. Sites selected for this study were in the moist semi‐deciduous forest zone and had nearly identical physiographic characteristics. In each of three natural forest stands and three teak plantations, 16 soil pits were examined and soil samples from the 0–20 (major rooting zone) and 20–40 cm depths were analyzed for selected chemical and physical properties. In the 0–20 cm depths bulk density significantly increased (1.17 to 1.30 g cm^‐3), but soil organic matter (OM) content (13 to 11%), total nitrogen (0.3 to 0.2 %), available phosphorus (4.2 to 1.2 mg kg^‐1), and exchangeable potassium (0.4 to 0.3 cmol(+)kg^‐1), calcium (17.0 to 12.4 cmol(+)kg^‐1), and magnesium (3.8 to 3.2 cmol(+)kg^‐1) significantly decreased in soils where natural forests were replaced with teak plantations. Similar results also were found for the 20–40 cm soil depths. The higher nutrient contents in soils under the natural forest may have been due to more litter contributions from understorey vegetation observed there. In the teak plantations nutrient leaching losses may have accelerated due to increased mineralization and the inability of teak to use the increase in available nutrient.     

The turnover of organic carbon in subsoils. Part 1. Natural and bomb radiocarbon in soil profiles from the Rothamsted long-term field experiments

The Rothamsted long‐term field experiments, started more than 150 years ago, provide unique material for the study of carbon turnover in subsoils. Total organic C, ¹⁴C and ¹³C were measured on soil profiles taken from these experiments, before and after the thermonuclear bomb tests of the mid‐20th century. Four contrasting systems of land management were sampled: land cultivated every year for winter wheat; regenerating woodland on acid soil; regenerating woodland on calcareous soil; and old grassland. The mean radiocarbon ages of all the pre‐bomb samples from cultivated land were 1210 years (0–23 cm), 2040 years (23–46 cm), 3610 years (46–69 cm) and 5520 years (69–92 cm). Bomb radiocarbon derived from thermonuclear tests was present throughout the profile in all the post‐bomb samples, although below 23 cm the amounts were small and the pre‐ and post‐bomb radiocarbon measurements were often not significantly different. Values of δ¹³C increased down the profile, from ?26.3‰ (0–23 cm layer, mean of all measurements) to ?25.2‰ for the 69–92 cm layer. The C/N ratios decreased with depth in virtually all of the profiles sampled. Excluding the surface (0–23 cm) soils from the old grassland, the hyperbola m = 152.1 ? 2341/(1 + 0.264n) gave a close fit to the radiocarbon data from all depths, all sampling times and all sites, where n is the organic C content of the soil, in t ha^?1, and m is the radiocarbon content of the soil, in Δ¹⁴C units, corrected for expansion or contraction of soil layers with time. The aberrant grassland soils almost certainly contained coal: one of them was shown by ¹³C‐NMR to contain 0.82% coal C. In Part 2 (this issue) of this pair of papers, these radiocarbon and total C measurements are used to develop and test a new model for the turnover of organic C in subsoils.     

Soil Organic Carbon and Nitrogen Fractions in Temperate Alley Cropping Systems

Abstract

Alley cropping may promote greater sequestration of soil organic carbon. The objective of this study was to examine spatial variability of soil organic carbon (C) and nitrogen (N) fractions relative to tree rows in established alley cropping systems in north central Missouri. Soils were collected to a depth of 30 cm from two alley cropped sites, a 19‐yr‐old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (pecan site) and an 11‐yr‐old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (maple site). Particulate organic matter (POM) C constituted 15–65% and 14–41% of total organic C (TOC) at the pecan and maple sites respectively, whereas POM N comprised 3 to 24% of total N (TKN). TOC and TKN were on average 13% and 18% higher at the tree row than at the middle of the alley for surface soils (0–10 cm) at the pecan site, respectively. Similarly, POM C was two to three times higher at the tree row than the alley for subsurface soils at the maple site. No differences in microbial biomass C and N between positions were observed. Observed results suggest the existence of spatially dependent patterns for POM C, TOC, and TKN, relative to tree rows in alley cropping.     

Soil hydraulic and physico-chemical properties of Ultisols and Inceptisols in south-eastern Nigeria

Understanding soil water dynamics and storage is important to avoid crop failure on highly weathered, porous and leached soils. The aim of the study was to relate soil moisture characteristics to particle-size distributions and chemical properties. On average, Atterberg limits were below 25% in the A-horizon and not more than26.56% in the B-horizon, whereas soil bulk density was between 1.27 and 1.66Mgm^?3. The saturated hydraulic conductivity (K_sat) was generally between 0.20 and 5.43 cm h^?1 in the top soil and <1.31 cm h^?1 in the subsoil. The higher K_sat values for the A-horizons were attributed to the influence soil microorganisms operating more in that horizon. The amount of water retained at field capacity or at permanent wilting point was greater in the B-horizons than in the A-horizons, suggesting that clay accumulation in the B-horizon and evapotranspiration effects in the A-horizon may have influenced water retention in the soils. Soil moisture parameters were positively related to clay content, silt content, exchangeable Mg²⁺, Fe₂O₃ and Al₂O₃, and negatively related to sand content, SiO₂, sodium absorption ratio, exchangeable sodium percentage and bulk density. The low clay content may explain why drainage was so rapid in the soils.     

Paddy management on different soil types does not promote lignin accumulation

Paddy soil management is generally thought to promote the accumulation of soil organic matter (SOM) and specifically lignin. Lignin is considered particularly susceptible to accumulation under these circumstances because of the recalcitrance of its aromatic structure to biodegradation under anaerobic conditions (i.e ., during inundation of paddy fields). The present study investigates the effect of paddy soil management on SOM composition in comparison to nearby agricultural soils that are not used for rice production (non‐paddy soils). Soil types typically used for rice cultivation were selected, including Alisol, Andosol and Vertisol sites in Indonesia (humid tropical climate of Java) and an Alisol site in China (humid subtropical climate, Jiangxi province). These soil types represent a range of soil properties to be expected in Asian paddy fields. All upper‐most A horizons were analysed for their SOM composition by solid‐state ¹³C nuclear magnetic resonance (NMR) spectroscopy and for lignin‐derived phenols by the CuO oxidation method. The SOM composition was similar for all of the above named parent soil types (non‐paddy soils) and was also not affected by paddy soil management. A substantial proportion (up to 23%) of the total aryl‐carbon in some paddy and non‐paddy soils was found to originate from condensed aromatic‐carbon (e.g ., charcoal). This may be attributed to the burning of crop residues. On average, the proportion of lignin was low and made up 20% of the total SOM, and showed no differences between straw, particulate organic matter (POM), and the bulk soil material. The results from CuO oxidation are consistent with the data obtained from solid‐state ¹³C NMR spectroscopy. The extraction of lignin‐derived phenols revealed low VSC (vanillyl, syringyl, cinnamyl) values for all investigated soils in a range (4 to 12 g kg⁻¹ OC) that was typical for agricultural soils. In comparison to adjacent non‐paddy soils, the data do not provide evidence for a substantial accumulation of phenolic lignin‐derived structures in the paddy soils, even for those characterized by higher organic carbon (OC) contents (e.g ., Andosol‐ and Alisol (China)‐derived paddy soils). We conclude that the properties of the parent soil types are more important for the lignin content of the soils than the effect of paddy management itself.     

Effect of compaction on pore functions of soils in a Saalean moraine landscape in North Germany

Soil compaction and related changes of soil physical parameters are of growing importance in agricultural production. Different stresses (70, 230, 500, and 1000 kPa) were applied to undisturbed soil core samples of eight typical soils of a Saalean moraine landscape in N Germany by means of a confined compression device to determine the effect on (1) total porosity/pore‐size distribution, (2) saturated hydraulic conductivity, and (3) air conductivity to assess the susceptibility towards compaction. Different deformation behaviors after exceeding the mechanical strength particularly resulted from a combination of soil characteristics like texture and initial bulk density. The saturated hydraulic conductivity, as an indicator for pore continuity, was largely affected by the volume of coarse pores (r² = 0.82), whereas there was no relationship between bulk density and saturated hydraulic conductivity. Since coarsely textured soils primarily possess a higher coarse‐pore fraction compared to more finely textured soils, which remains at a high level even after compaction, only minor decreases of saturated hydraulic conductivity were evident. The declines in air conductivity exceeded those in hydraulic conductivity, as gas exchange in soils is, besides the connectivity of coarse pores, a function of water content, which increases after loading in dependence of susceptibility to compaction. A soil‐protection strategy should be focused on more finely textured soils, as stresses of 70 kPa may already lead to a harmful compaction regarding critical values of pore functions such as saturated hydraulic conductivity or air capacity.     

Different responses in bulk density and saturated hydraulic conductivity to soil deformation by logging machinery on a Ferralsol under native forest

Ferralsols have high structural stability, although structural degradation has been observed to result from forest to tillage or pasture conversion. An experimental series of forest skidder passes in an east Amazonian natural forest was performed for testing the effects of mechanical stress during selective logging operations on a clay‐rich Ferralsol under both dry and wet soil conditions. Distinct ruts formed up to 25 cm depth only under wet conditions. After nine passes the initially very low surface bulk density of between 0.69 and 0.80 g cm^?3 increased to 1.05 g cm^?3 in the wet soil and 0.92 g cm^?3 in the dry soil. Saturated hydraulic conductivities, initially >250 mm h^?1, declined to a minimum of around 10 mm h^?1 in the wet soil after the first pass, and in the dry soil more gradually after nine passes. The contrasting response of bulk density and saturated hydraulic conductivity is explained by exposure of subsoil material at the base of the ruts where macrostructure rapidly deteriorated under wet conditions. We attribute the resultant moderately high hydraulic conductivities to the formation of stable microaggregates with fine sand to coarse silt textures. We conclude that the topsoil macrostructure of Ferralsols is subject to similar deterioration to that of Luvisols in temperate zones. The stable microstructure prevents marked compaction and decrease in hydraulic conductivity under wetter and more plastic soil conditions. However, typical tropical storms may regularly exceed the infiltration capacity of the deformed soils. In the deeper ruts water may concentrate and cause surface run‐off, even in gently sloping areas. To avoid soil erosion, logging operations in sloping areas should therefore be restricted to dry soil conditions when rut formation is minimal.