Changes in soil acidity and related variables over 25 years in the North Pennine Uplands, UK

Abstract. Soil profiles, first sampled between 1963 and 1973, were resampled in 1991 in an upland area with modertely high deposition of pollutants. One hundred horizons from 32 profiles, representing 10 different soil subgroups were analysed for pH and seven variables related to pH, using the same laboratory methods on both sampling occasions. To allow comparisons to be made with results obtained with these old methods, analysis of the 1991 samples was repeated for some determinands using the methods currently used in the analytical laboratory. Organic and A horizons show a consistent increase in acidity between samplings. Although brown soils and lithomorphic soils have increased in acidity throughout their depth, gleys and podzols have decreased in acidity at depth, probably because of poor water transmission downwards into these horizons. Correlations with other determinands suggest that the dominant process in the soils is leaching of basic cations and their replacement on exchange sites by protons and probably aluminium ions. A cause of the increase in soil acidity is likely to be the deposition of atmospherically transported pollutants.     

Effect of biogas slurry addition on soil properties,yields, and bacterial composition in the rice-rape rotation ecosystem over 3 years

Journal of Soils and Sediments - Organic treatments may improve soil nutrient availability and ecological functions. This study aimed to determine the effect of biogas slurry (BS) on soil...     

Impact of biochar on red paddy soil physical and hydraulic properties and rice yield over 3 years

Journal of Soils and Sediments - Biochar is a promising soil amendment to improve soil quality. This study was conducted to understand the effect of biochar on soil physical and hydraulic...     

Runoff and sediment variation and attribution over 60 years in typical Loess Plateau basins

Purpose

The trends in runoff and sediment transportation in typical Loess Plateau basins and the factors causing the changes need to be clarified.

Materials and methods

In this study, the runoff and sediment transportation data from 1960 to 2016, from hydrological stations (Wenjiachuan, Baijiachuan, Ganguyi, and Zhuangtou) based in four typical basins, were analyzed systematically using linear regression, anomaly accumulation, the Mann–Kendall test, and double accumulation curve. The characteristics of the runoff and sediment transportation and their responses to climatic and anthropogenic activities were investigated using several hydrological analytical and statistical methods.

Results and discussion

The results indicate that both runoff and sediment transportation in the four typical basins have decreased sharply from 1960 to 2016. Since the implementation of the Grain-for-Green Project in 1999, the reduction has been more marked, in particular the runoff and sediment discharge of the Kuye River (Wenjiachuan station). Compared with the period 1960–1999, the average annual runoff and sediment discharge in 2000–2016 had decreased by 76.72% and 94.50%, respectively. Apart from the Wuding River (Baijiachuan station), an abrupt change in runoff and sediment transportation in the basins occurred within 2–7 years of the implementation of the Grain-for-Green Project.

Conclusions

In general, returning farmland to forests (grass) has had a more pronounced effect on the reduction of runoff and sediment in the more northerly Kuye River (Wenjiachuan station) and Wuding River (Baijiachuan station) basins, compared with the more southerly Yanhe River (Ganguyi station) and Beiluo River (Zhuangtou station) basins.

     

Surface water acidification in the UK; current status,recent trends and future predictions

Data collected at 22 lake and stream sites under the UK Acid Waters Monitoring Network, established in 1988, are assessed. Non-marine sulphate concentrations in surface waters largely reflect the sulphur deposition gradient across the country. Time series analysis indicates an increase in non-marine sulphate concentrations at sites in SW Scotland, the Lake District and in Wales. No similar trends have been detected in deposition data for the same period. Predictions of water chemistry response at each site to the new UNECE sulphur protocol have been made using a long-term, dynamic acidification model (MAGIC). The results indicate that the agreed emissions reductions will lead to recovery at many sites over a 15–20 year timescale but will have little effect at the most impacted sites, within the next 15 years.     

Changes in soil properties related to conversion of savannah woodland into pine and eucalyptus plantations,Northern Nigeria

Soil properties associated with six age-grade plantations of Pinus oocarpa Schiede and Eucalyptus camaldulensis Dehnh., respectively, including nearby natural vegetation, were compared in the savannah zone of Nigeria. The soil organic matter, total nitrogen and exchangeable nutrients first show declining values with the increasing age of the plantation, then an increase and finally steady or declining values in the 0–15 cm soil depth. Usually the differences between the two youngest plantations and the oldest plantations, and the natural vegetation, were significant. In the 20–30 cm soil depth the properties showed a decrease or steady values over time, with the three oldest plantations showing significant differences from the natural vegetation. The soil pH showed an increased acidity over time. There was little difference in the soil properties between the two tree species. The implications of the results are discussed in relation to sustaining productivity and soil fertility. © 1998 John Wiley & Sons, Ltd.     

Effects of 10 years of conservation tillage on soil properties and productivity in the farming–pastoral ecotone of Inner Mongolia, China

Soil degradation and subsequent yield decline are the main factors limiting further development of agriculture on the farming–pastoral transition zone of China. A 10-year field experiment was conducted in Inner Mongolia to compare the long-term effects of no-tillage with straw cover (NT), subsoiling with straw cover (ST), rototilling with straw cover (RT) and traditional tillage (TT) using ploughs on soil properties and productivity in a spring wheat–oat cropping system. Long-term conservation tillage increased soil organic matter in the top 20 cm by 21.4%, total N by 31.8% and Olsen's P by 34.5% in the 0–5 cm layer compared to traditional tillage. Mean percentage of macro-aggregates (>0.25 mm, +20%) and macroporosity (>60 μm, +52.1%) also improved significantly in the 0–30 cm soil layer ( P  <   0.05). The largest yield improvements coupled with greatest water use efficiency (WUE) were achieved by no-tillage with straw cover. Ten-year mean crop yields increased by 14.0% and WUE improved by 13.5% compared to traditional tillage due to greater soil moisture and improved soil physical and chemical status. These improvements in soil properties and productivity are of considerable importance for the seriously degraded soils in semiarid Inner Mongolia, as well as for food security, sustainable agriculture and carbon storage in the farming–pasture transition regions of China.     

Changes in phosphorus and potassium contents in soddy-podzolic soil under pasture at the long-term surface application of mineral fertilizers

Experiments performed on sandy loamy gleyic soddy-podzolic soil at the Vezaiciai Branch of the Lithuanian Institute of Agriculture showed that, after liming to specified pH levels at the annual surface application of mineral fertilizers to pastures, the greatest change in the pH KCl and P₂O₅ and K₂O accumulations occurred in the upper (0-to 5-cm) layer of the plow horizon, which indicated the important role of grassing systems in hampering the migration of nutrients.     

Changes in water content in and under frozen soil in Iowa,U.S.A.

Water contents were measured in a soil profile during the winter from the time of harvest until soil temperatures were greater than 0°C through this profile in the spring. Water movement between successive layers was predicted using the Darcy flow law and changes in water flux. These values were then compared with the changes in soil water content observed in field measurements. Results showed that water content changes (accumulation or loss) below the frozen layer were greater than predicted but that the differences between predicted and measured contents were small, much smaller than the amounts reported in previous experiments.     

Changes of pore morphology, infiltration and earthworm community in a loamy soil under different agricultural managements

Earthworm activity produces changes at different scales of soil porosity, including the mesoporosity (between 1.000 and 30 μm eq. dia.) where both water retention and near-saturated infiltration take place. At this scale, the structural changes are poorly described in temperate agricultural systems, so we do not yet fully understand how these changes occur. The present study was conducted to determine the relationships between the morphology of the mesopores, which is mainly affected by earthworm activity, and the hydrodynamic behaviour (near-saturated infiltration) of topsoil under different agricultural managements inducing a large range of earthworm populations.Investigations were carried out at the soil surface in three fields under different management practices giving rise to three different earthworm populations: a continuous maize field where pig slurry was applied, a rye-grass/maize rotation (3/1 year, respectively) also with pig slurry, and an old pasture sown with white clover and rye-grass.Pore space was quantified using a morphological approach and 2D image analysis. Undisturbed soil samples were impregnated with polyester resin containing fluorescent pigment. The images were taken under UV light, yielding a spatial resolution of 42 μm pixel⁻¹. Pores were classified according to their size (which is a function of their area) and their shape. Hydraulic conductivity K(h) was measured using a disc infiltrometer at four water potentials: −0.05, −0.2, −0.6, and −1.5 kPa. The abundance and ecological categories groups of earthworms were also investigated.Continuous soil tillage causes a decrease in both abundance and functional diversity (cf. maize compared with old pasture) when soil tillage every 4 years causes only a decrease in abundance (cf. rotation compared with old pasture). There were no relationships between total porosity and effective porosity at h=−0.05 kPa. Image analysis was useful in distinguishing the functional difference between the three managements. Fewer roots and anecic earthworms resulted in fewer effective tubular voids under maize. There were fewer packing voids in the old pasture due to cattle trampling. Greater hydraulic conductivity in the pasture phase of rotation may arise from a greater functional diversity than in the maize and absence of cattle trampling compared with the pasture. We point to some significant differences between the three types of agricultural management.A better understanding is required of the influence of agricultural management systems on pore morphology. This study provides a new methodology in which we consider the earthworm activity as well as community in order to assess the effects of agricultural management on soil structure and water movement.     

Response of soil water chemistry and fine-roots to clean rain in a spruce forest ecosystem at Solling,FRG

In the Solling experimental forest in central Germany a ‘clean rain’ roof experiment is conducted in a 60 year old Norway Spruce (Picea abies KARST.) stand. In this experiment with application of artificially prepared pre-industrial throughfall there is now a time series of soil water chemistry data from about 2 yr of pre-experiment and 3.5 yr of manipulation treatment. The response of soil solution chemistry to reduced inputs of N and S was strong and fairly rapid. There is a clear reflection of reduced input in soil solution concentrations, particularly for the N ions. The fine-roots of the Norway spruce trees reacted strongly to these changes in soil water chemistry. Fine-root biomass increased in the clean rain plot by about 40 % compared to pre-experimental conditions. This increase was strongest in the B-horizon, indicating that acid stress has ameliorated in the mineral soil. However, low concentrations of ammonium and nitrate in the root zone may also have contributed to this effect, since more fineroots are needed to maintain the N demand of the trees. No effect was yet found for other variables (photosynthesis, respiration, transpiration). Nutrient cation concentrations in the needles remained on the same low level as in the control groups. However, these aboveground variables may react after some time lag. The results demonstrate that in spruce forests on acid soil atmospheric element input largely controls soil solution chemistry and that air pollution control measures would have a significant effect with respect to ameliorating soil water chemistry, acidity and forest health.     

Changes in soil chemistry and aggregate stability induced by fertilizer applications, burning and trash retention on a long-term sugarcane experiment in South Africa

Throughout the world there is a trend towards retaining crop residues rather than burning them. For this reason, changes in soil chemistry and aggregation in a Vertisol induced by 59 years of burning or green cane harvesting with or without annual fertilizer applications were investigated. Crop residues were either burnt prior to harvest with the harvest residues raked off (R₁), burnt prior to harvest with the harvest residues left on the soil surface (R₂), or left unburnt with all the trash left on the soil surface (R₃). Concentrations of organic C in the surface 10 cm of soil increased with fertilizer applications and with increasing amounts of crop residue returned in the order R₁ < R₂ < R₃. Fertilizer applications caused an accumulation of residual P in both inorganic (Pi) and organic (Po) forms. A sequential P fractionation showed that fertilizer P accumulated in both labile and recalcitrant Pi and Po forms, and trash retention caused an accumulation of recalcitrant Po. Concentrations of K decreased in the unfertilized R₁ and R₂ treatments because K reserves were depleted. By contrast, there was an increase in the concentrations of K in the fertilized R₃ treatment. The soil became more acid on the fertilized and, to a lesser extent, trash retention plots. We attribute this to nitrification and subsequent nitrate leaching. Acidification resulted in a loss of exchangeable Ca and Mg, a decrease in ECEC, and an increase in the concentrations of total and monomeric Al in soil solution, in exchangeable Al³⁺ and in the buffering reserve of non‐exchangeable Al associated with organic matter. Aggregate stability was increased by increasing crop residues but decreased by fertilizer applications. The decrease was attributed to an increase in the proportion of exchangeable cations present in monovalent form due to applications of fertilizer K and leaching of Ca and Mg. We conclude that trash retention and annual fertilizer applications have substantial long‐term effects on both organic matter status and soil pH and therefore on other soil chemical and physical properties.     

Changes in soil microbial biomass, metabolic quotient, and organic matter turnover under Hieracium (H. pilosella L.)

 In New Zealand Hieracium is an opportunistic plant that invades high country sites more or less depleted of indigenous vegetation. To understand the invasive nature of this weed we assessed the changes in soil C, N and P, soil microbial biomass C, N and P contents, microbial C : N and C : P ratios, the metabolic quotient, and turnover of organic matter in soils beneath Hieracium and its adjacent herbfield resulting from the depletion of tussock vegetation. The amounts of soil organic C and total N were higher under Hieracium by 25 and 11%, respectively, compared to soil under herbfield. This change reflects an improvement in both the quantity and quality of organic matter input to mineral soil under Hieracium, with higher percentage organic C and a lower C : N ratio. The microbial biomass C, N and P contents were also higher under Hieracium. The amount of C respired during the 34-week incubation indicated differences in the nature of soil organic matter under Hieracium, the unvegetated "halo" zone surrounding Hieracium patches, and herbfield (depleted tussock grassland). Decomposition of organic matter in these zones showed that the Hieracium soil had the greatest rate of CO₂ respired, and the halo soil had the lowest. We relate the enhanced organic C turnover to the invasive nature of Hieracium. Net N mineralization was significantly lower from the Hieracium soil (57 mg N g^–1 soil N) than from herbfield and halo soils (74 and 71 mg N g^–1 soil N, respectively), confirming that the nature of organic N in Hieracium soil is different from adjoining halo and herbfield soils. It seems plausible that specific compounds such as polyphenols and lignins released by Hieracium are not only responsible for increased organic N, but also control the form and amount of N released during organic matter transformations. We conclude that the key to the success of Hieracium in the N-deficient South Island high country of New Zealand lies in its ability to control and sequester N supply through modifying the soil organic matter cycle. Received: 1 December 1998     

Carbon mineralization in an organic soil, with and without added grass litter, from a high-CO2 environment at a carbon dioxide spring

Both CO₂-C production and the decomposability of grass leaf litter in a gley soil from a naturally occurring CO₂ spring were previously shown to be influenced by the atmospheric CO₂ concentrations under which the soil and litter were sampled. Here we investigate C mineralization in an organic soil from very high CO₂ environments (range 1220-3900 μl l⁻¹) at the same spring, and the effect of added leaf litter on CO₂-C production. Carbon mineralization in the organic soil was unusual in two respects: (1) the proportion of labile components was very high, with more than 11% of the initial soil C being metabolized to CO₂-C after 56 d at 25 °C; (2) rates of CO₂-C production in autumn samples increased on incubation, after an initial decline. Decomposition was initially more rapid in C3 Holcus lanatus (Yorkshire fog) than in C4 Pennisetum clandestinum (kikuyu) litter, but differed little in samples from different atmospheric CO₂ concentrations. Overall, the effects of environmental variables on estimates of litter decomposability in the organic soil were similar to, although much less marked than, those in the gley soil. Results suggest that organic components in the organic soil were metabolized at least as readily as those of added litter during the later stages of the 56-d incubation.     

Changes in enzyme activities and soil microbial community composition along carbon and nutrient gradients at the Franz Josef chronosequence, New Zealand

During primary succession, the abundance of carbon (C) and nitrogen (N) in soil increases, while phosphorus (P) declines. These changes in nutrient concentrations in organic matter are likely to play an important role in controlling enzyme-mediated nutrient mineralization. We examined how enzyme activity and efficiency changed with successional time in organic and mineral soils taken from the 120 000-year-old Franz Josef soil development sequence, New Zealand, and the relationship between enzyme activity and efficiency and soil nutrient concentrations. We found that the activity of enzymes involved in P mineralization increased with site age across the Franz Josef chronosequence, while the activity of enzymes regulating C and N mineralization declined in organic but not mineral soil. Sulfatase activity peaked at an intermediate-aged site, possibly indicating a transient period of S limitation. The activity of phosphatase enzymes was negatively correlated with the concentration of P in the soil, whereas activity of C-, N- and S-hydrolyzing enzymes was not strongly dependent on nutrient concentrations. When assessed as efficiency (activity per unit microbial biomass), there were strong patterns of increasing efficiency of P-, and decreasing efficiency of C- and N-hydrolyzing enzymes with site age. We suggest that activity patterns for C-, N- and S-hydrolyzing enzymes were obscured by simultaneous and opposing changes in enzyme efficiency and microbial biomass. In mineral soil, efficiency of enzymes was negatively correlated with soil nutrient availability. In contrast, in organic soil, efficiency of C-, N- and S-hydrolyzing enzymes was positively correlated with soil P, while efficiency of P-hydrolyzing enzymes was negatively correlated with soil P. The increase in efficiency of P-hydrolyzing enzymes, and decrease in efficiency of C-, N- and S-hydrolyzing enzymes with site age was accompanied by a shift in microbial community composition towards higher relative abundances of fungi. Changes in enzyme efficiency with site age are likely to be due to both constitutive differences in enzyme production, and down-regulation of enzyme expression.     

Changes in microbial biomass C, soil carbohydrate composition and aggregate stability induced by growth of selected crop and forage species under field conditions

The effects of growth of various crop and forage species on microbial biomass C, soil carbohydrate content and monosaccharide composition, and mean weight diameter (MWD) were investigated in two field experiments. One experiment was conducted over one growing season (4 months) whereas the other had been conducted for three consecutive growing seasons (32 months). In the four-month experiment, aggregate stability (estimated as MWD) of soil from experimental plots followed the order Italian ryegrass > prairie grass > phacelia = pea = maize. At the 32-month site the order was perennial ryegrass > annual ryegrass > perennial white clover = barley. At both sites crops with the greatest root mass and root length density had the greatest effect on increasing MWD. In all cases, rhizosphere soil had a significantly higher microbial biomass and MWD than non-rhizosphere soil. However, organic C, total content of acid-hydrolysable carbohydrate and content of individual monosaccharides in acid hydrolysates were similar in rhizosphere and non-rhizosphere soil. The fraction of soil carbohydrate extractable with hot water (representing about 6-8% of the total carbohydrate content) was significantly higher in the rhizosphere soil. This fraction has a galactose plus mannose over arabinose plus xylose ratio of 2.1–2.3 indicating that it was predominantly of microbial origin. It is suggested that the carbohydrate fraction extractable with hot water is made up of exocellular microbial polysaccharides that are involved in stabilizing soil aggregates in the rhizosphere. By comparison with arable crop species, grass species have a larger root mass and root length density, and therefore a higher microbial biomass and larger production of carbohydrate extractable with hot water. As a result they have a more marked effect on improving soil aggregate stability.     

Organic carbon and nitrogen in soil particle-size aggregates under dry tropical forests from Guanacaste,Costa Rica — Implications for within-site soil organic carbon stabilization

In this study we report results on the soil organic carbon (SOC) pool (0–50 cm) from a chrono-sequence of dry tropical forest (dTf) of increasing age and a yearly burned ancient pasture in the “Sector Santa Rosa” at the “Área de Conservación Guanacaste” (ACG) in northwestern Costa Rica, where intense human induced land-use modifications has occurred during the past century. The effects of land conversion on soil organic carbon (SOC) have mainly been conducted in the Atlantic humid forests while overlooking dTfs. We quantified the depth distribution of SOC concentration down to 50-cm and in physically separated mineral soil fractions, as these data are scanty from the dTf. Additional objectives were to identify the relationship with selected soil physical and chemical properties, including stabilized SOC fractions by means of multivariate ordination methods. Statistically significant differences were found for the main fixed factor ecosystem for all soil variables analyzed (ANOVA). SOC and N concentrations were significantly higher in the oldest dTf compared to the other dTfs. Soil physical properties like aggregate size distribution and bulk density changed with depth, and varied significantly among the three dTf stands sampled. The multivariate analysis, i.e. between-within class principal component analysis (PCA), revealed a significant ordination of dTfs (P < 0.0001). The SOC concentration decreased in particle size fractions of < 200 μm aggregates with increasing soil depth. The lowest and highest C concentrations were obtained in the fine sand (105–200 μm) and clay + silt (< 20 μm) fractions, respectively. Mineral-associated and stable SOC pool increased with depth, and poorly crystalline Fe oxides and ferrihydrite were the most important minerals for SOC stabilization at 40–50 cm depth. The highest SOC pool was found in the old-growth and > 80 years-old dTfs, i.e., 228.9 and 150.3 Mg C ha^− 1, respectively, values similar to those obtained in the Atlantic humid forests of Costa Rica. Comparatively to other studies, soils under dTf at Santa Rosa store a considerable amount of SOC with potentially large CO2 emissions if this ecosystem is not preserved.     

n-Alkanes and free fatty acids in humus and A1 horizons of soils under beech, spruce and grass in the Massif-Central (Mont-Lozère), France

Soil profiles under beech, spruce and a grassland have been analysed to study the evolution of natural n-alkanes in pollution-free ecosystems. The soils had all developed on granitic bedrock, at an altitude of 1300–1500 m in the region of Mont-Lozère (southern Massif-Central, France). In contrast to the grassland soil, the two forest soils both possessed a well-developed acidic moder humus-type horizon. This could be subdivided as follows: fresh litter (OL), fragmentation (OF) and humification (OH) layers; two litters, one fresh (OL1) and one old (OL2) could actually be distinguished in the beech forest soil. The n-alkane signature of the parent plants was preserved in the top litter. Immediately underneath, in the OF layer(s) the original n-alkane signatures were progressively but rapidly replaced by a common signature composed of n-C₂₇ and n-C₂₅ with larger proportions of the former than of the latter. These two hydrocarbons were most probably produced in situ by fungi. These results appear to illustrate the action of soil microorganisms which metabolize the inherited n-alkanes and produce new compounds of the same family. Unlike the alkanes and the low molecular weight fatty acids ≤ C₂₀ (which increase greatly in the OL2 layer under beech as a result of intense microbial activity), the heavy fatty acids (> C₂₀) show no significant change in the organic horizon.     

Decomposition in soil of specifically 14C-labeled model and cornstalk lignins and coniferyl alcohol over two years as influenced by drying,rewetting, and additions of an available C substrate

Losses of 2-side chain and ring-carbons of coniferyl alcohol units in model and cornstalk lignins were about 22, 33 and 40% after 6, 12 and 24 months incubation in a neutral sandy loam top soil. Comparable values for the O¹⁴CH₃ carbons were 46, 66 and 69%, respectively. The free coniferyl alcohols decomposed more rapidly during the first 6–9 months and C loss values for the ring- and 2-side chain carbons were about 47% at 6 months and 58% at 2 yr. Loss of the OCH₃ C was about 61% at 6 months and 72% at 2 yr. The addition of ground cornstalks at 0, 6, 12 and 18 months did not influence the total amount of ¹⁴C evolved from any of the treatments. During the first week after the fresh cornstalk additions at 6 months the amount of ¹⁴C evolved was increased from about 0.3% to 0.8% of the applied activity. After 1 month, however, losses from the controls were the same as for the supplemental treatments.