Factors controlling the erosion rates in a semi-arid zone (Bardenas Reales,NE Spain)

Bardenas Reales is an erosive depression 415 km² in area located in the central-western part of the Ebro Depression. Tertiary sediments crop out in the margin of the basin whereas Quaternary sediments, Holocene in age, occur only in its centre. These Holocene sediments (clays and silts) are the result of the erosion and weathering of the Tertiary clays and are made up of 3 different stratigraphic units. Erosion is clearly the dominant process in the centre of the depression, generating gullies up to 10 km in long and 8 m deep. In order to analyse and quantify the erosion rates of the studied area, erosion was measured on two Soil Erosion Plots with volumetric and instrumental techniques that have been supplied for the last 12 years. The results show that the estimated erosion rates depend extrinsically on the used method and intrinsically on the time of the year in which they are measured. The most accurate values are those obtained by means of collector devices. The values obtained by the microtopographic profile gauge are overestimated, while the results of the measurement with erosion pins are clearly lower. The study area is located in a semi-arid environment, with two pluviometric maximums, in spring and autumn, associated with convective storms. In summer and winter, rainfall is related to Atlantic cyclonal fronts. Soil loss is significant during the pluviometric maximums when rainfall quantity and intensity are higher. During cyclonal periods, in contrast, water erosion is null or scarce and soil loss is related to mudflows. In addition, the erosion rates of each Holocene unit are different. The C2 Holocene unit has undergone greater erosion because of its physico-chemical properties. All the stratigraphic units have similar characteristics regarding Tertiary materials. Since 1993 the average erosion rate measured by the collector device on the Tertiary materials is 32 Mg ha^− 1 year^− 1 and 77 Mg ha^− 1 year^− 1 in the Holocene.     

Impacts of 22-year organic and inorganic N managements on soil organic C fractions in a maize field,northeast China

Impacts of 22-year organic and inorganic N managements on total organic carbon (TOC), water-soluble organic C (WSOC), microbial biomass C (MBC), particulate organic C (POC) and KMnO₄ oxidized organic C (KMnO₄-C) concentrations, C management index (CMI), and C storage in surface soil (0–20 cm) were investigated in a maize (Zea may L.) field experiment, Northeast China. The treatments included, CK: unfertilized control, M: organic manure (135 kg N ha^− 1 year^− 1), N: inorganic N fertilizer (135 kg N ha^− 1 year^− 1) and MN: combination of organic manure (67.5 kg N ha^− 1 year^− 1) and inorganic N fertilizer (67.5 kg N ha^− 1 year^− 1). TOC concentration and C storage were significantly increased under the M and MN treatments, but not under the inorganic N treatment. The organic treatments of M and MN were more effective in increasing WSOC, MBC, POC and KMnO₄-C concentrations and CMI than the N treatment. The M treatment was most effective for sequestrating SOC (10.6 Mg ha^− 1) and showed similar increase in degree of grain yield to the N and MN treatments, therefore it could be the best option for improving soil productivity and C storage in the maize cropping system.     

Effect of snow amount on runoff,soil loss and suspended sediment during periods of snowmelt in southern West Siberia

Surface runoff, soil loss, suspended sediment concentration (SSC), texture of eroded soils and suspended sediment were determined on slightly eroded chernozems (mouldboard fall-ploughed) during years with different amounts of snow in three areas of southern West Siberia (Predsalairye, Priobye and Kuznetsk hollow). These areas have different geomorphological and climatic characteristics and soils. Observations were made from 1969 to 2007. The soil loss during very low-snow and low-snow years did not exceed 2 t ha^− 1. After winters with normal amounts of snow, the runoff led to slight soil loss (2–5 t ha^− 1). Soil losses in high-snow and very high-snow years varied from slight to severe (4.8–15.8 t ha^− 1) depending on studied area. The main sediment exported during intensive snowmelt and the 1 mm of runoff transported from 35 to 150 kg ha^− 1 of soil material. The removal of soil particles < 0.01 mm (especially clay) prevailed during the initial and final stages of snowmelt. Clay removal by meltwater from the ploughed layer in high-snow and very high-snow years varied from 3300 to 4200 kg ha^− 1 and, in the initial and final stages of snowmelt clay removal, accounted for 1260–1,500 kg ha^− 1. Among the three studied regions, Predsalairye had decreased soil erosion resistance and was the area with the greatest danger of erosion.     

Soil loss tolerance limits for planning of soil conservation measures in Shivalik–Himalayan region of India

Soil loss tolerance limit is defined as the threshold upper limit of soil erosion that can be allowed without degrading long term productivity of specific soils. In India a default soil loss tolerance limit (SLTL) of 11.2 Mg ha^− 1 yr^− 1 is followed for planning soil conservation activities. The objective of this investigation is to provide a methodology to estimate quantitative SLTL for the Shivalik–Himalayan region in India for suggesting suitable soil conservation measures. A quantitative model was used to integrate potential soil indicators such as infiltration rate, bulk density, water stable aggregate, organic carbon and fertility status to assess soil quality governing soil resistibility to erosion. Scaling functions were used to convert soil parameters to unit less 0 to 1 scale. Normalized values of soil parameters were then multiplied by assigned weights based on relative importance and sensitivity analysis of each indicator. Soils were grouped into 1, 2 and 3 depending on overall additive score. A general guideline developed by the USDA-Natural Resource Conservation Service (NRCS) was followed with certain modifications in depth category for estimation of SLTLs. Soil loss tolerance limits varied from 2.5 to 12.5 Mg ha^− 1 yr ^− 1 compared to single value of 11.2 Mg ha^− 1 yr ^− 1 being followed earlier. Consideration of the newly estimated SLTLs would facilitate site specific conservation planning and prioritising areas for watershed management activities in India.     

The role of tree leaf mulch and nitrogen fertilizer on turfgrass soil quality

 The influence of tree leaf amendment and N fertilization on soil quality in turfgrass environments was evaluated. Our objective was to assess changes in soil quality after additions of leaf materials and N fertilization by monitoring soil chemical and physical parameters, microbial biomass and soil enzymes. Established perennial ryegrass (Lolium perenne) plots were amended annually with maple (Acer spp.) leaves at three different rates (0, 2240, and 4480 kg ha^–1 year^–1) and treated with three nitrogen rates (0, 63, and 126 kg N ha^–1 year^–1). Tree leaf mulching did not significantly affect water infiltration or bulk density. However, trends in the data suggest increased infiltration with increasing leaf application rate. Tree leaf mulching increased total soil C and N at 0–1.3 cm depth but not at 1.3–9.0 cm. Extracted microbial phospholipid, an indicator of microbial biomass size, ranged from 28 to 68 nmol phospholipid g^–1 soil at the 1.3–9.0 cm depth. The activity of β-glucosidase estimated on samples from 0–1.3 cm and 1.3–9.0 cm depths, and dehydrogenase activity estimated on samples from 1.3–9.0 cm were significantly increased by leaf mulching and N fertilizer application. Changes in microbial community composition, as indicated by phospholipid fatty acid methyl ester analysis, appear to be due to seasonal variations and did not reflect changes due to N or leaf amendment treatments. There were no negative effects of tree leaf mulching into turfgrass and early data suggest this practice will improve soil chemical, physical, and biological structure. Received: 10 December 1997     

Assessing soil erosion and control factors by the radiometric technique in the Boussouab catchment,Eastern Rif,Morocco

In the Eastern Rif of N Morocco, soil conservation is seriously threatened by water erosion. Large areas of soil have reached an irreversible state of degradation. In this study, the ¹³⁷Cs technique was used to quantify erosion rates and identify the main factors involved in the erosion process based on a representative catchment of the Eastern Rif. To estimate erosion rates in terms of the main factors affecting soil losses, samples were collected taking into account the lithology, slope and land use along six selected transects within the Boussouab catchment. The transects were representative of the main land uses and physiographic characteristics of that Rif sector. The reference inventory for the area was established at a stable, well preserved, matorral site (value of 4250 Bq m^− 2). All the sampling sites were eroded and ¹³⁷Cs inventories varied widely (between 245 and 3670 Bq m^− 2). The effective soil losses were also highly variable (between 5.1 and 48.8 t ha^− 1 yr^− 1). Soil losses varied with land use. The lowest average values were on matorral and fallow land (10.5 and 15.2 t ha^− 1 yr^− 1, respectively) but much higher with alfa vegetation or cereal crops (31.6 and 27.3, respectively). The highest erosion rate was on a badland transect at the more eroded part of the catchment, with rates exceeding 40 t ha^− 1 yr^− 1 and reaching a maximum of 48.8 t ha^− 1 yr^− 1.The average soil losses increased by more than 100% when the slope increased from 10° (17.7 t ha^− 1 yr^− 1) to 25° (40. 8 t ha^− 1 yr^− 1). Similar results were obtained when comparing erosion rates in soils that were covered by matorral with respect to those under cultivation. Lithology was also a key factor affecting soil loss. Soils on marls were more erodible and the average erosion rates reached 29.36 t ha^− 1 yr^− 1, which was twice as high as soils on the glacis and old fluvial terraces (average rates of 14.98 t ha^− 1 yr^− 1). The radiometric approach was very useful to quantify erosion rates and to examine the pattern of soil movement. The analysis of main erosion factors can help to promote rational soil use and establish conservation strategies in the study area.     

Effects of 30-year-old Aleppo pine plantations on runoff,soil erosion,and plant diversity in a semi-arid landscape in south eastern Spain

Forest management policies in Mediterranean areas have traditionally encouraged land cover changes, with the establishment of tree cover (Aleppo pine) in natural or degraded ecosystems for soil conservation purposes: to reduce soil erosion and to increase the vegetation structure. In order to evaluate the usefulness of these management policies on reduced erosion in semi-arid landscapes, we compared 5 vegetation cover types (bare soil, dry grassland, shrublands, afforested dry grasslands and afforested thorn shrublands), monitored in 15 hydrological plots (8 × 2 m), in the Ventós catchment (Alicante, SE Spain), over 4 years (1996 to 1999). Each cover type represented a different dominant patch of the vegetation mosaic on the north-facing slopes of this catchment. The results showed that runoff coefficients of vegetated plots were less than 1% of the precipitation volume; whereas runoff in denuded areas was nearly 4%. Soil losses in vegetation plots averaged 0.04 Mg ha^− 1 year^− 1 and increased 40-fold in open-land plots. The evaluation of these forest management policies, in contrast with the natural vegetation communities, suggests that: (1) thorn shrublands and dry grassland communities with vegetation cover could control runoff and sediment yield as effectively as Aleppo pine afforestation in these communities, and (2) afforestation with a pine stratum improved the stand's vertical structure resulting in pluri-stratified communities, but reduced the species richness and plant diversity in the understorey of the plantations.     

Long-term application of organic manure and nitrogen fertilizer on N2O emissions, soil quality and crop production in a sandy loam soil

A long-term field experiment was established to determine the influence of mineral fertilizer (NPK) or organic manure (composed of wheat straw, oil cake and cottonseed cake) on soil fertility. A tract of calcareous fluvo-aquic soil (aquic inceptisol) in the Fengqiu State Key Experimental Station for Ecological Agriculture (Fengqiu county, Henan province, China) was fertilized beginning in September 1989 and N₂O emissions were examined during the maize and wheat growth seasons of 2002-2003. The study involved seven treatments: organic manure (OM), half-organic manure plus half-fertilizer N (1/2 OMN), fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (PK) and control (CK). Manured soils had higher organic C and N contents, but lower pH and bulk densities than soils receiving the various mineralized fertilizers especially those lacking P, indicating that long-term application of manures could efficiently prevent the leaching of applied N from and increase N content in the plowed layer. The application of manures and fertilizers at a rate of 300 kg N ha⁻¹ year⁻¹ significantly increased N₂O emissions from 150 g N₂O-N ha⁻¹ year⁻¹ in the CK treatment soil to 856 g N₂O-N ha⁻¹ year⁻¹ in the OM treatment soil; however, there was no significant difference between the effect of fertilizer and manure on N₂O emission. More N₂O was released during the 102-day maize growth season than during the 236-day wheat growth season in the N-fertilized soils but not in N-unfertilized soils. N₂O emission was significantly affected by soil moisture during the maize growth season and by soil temperature during the wheat growth season. In sum, this study showed that manure added to a soil tested did not result in greater N₂O emission than treatment with a N-containing fertilizer, but did confer greater benefits for soil fertility and the environment.     

A preliminary assessment of the potential for using Pbex measurement to estimate soil redistribution rates on cultivated slopes in the Sichuan Hilly Basin of China

In order to assess its potential for estimating soil redistribution rates, the naturally occurring fallout radionuclide ²¹⁰Pb_ex has been used in parallel with ¹³⁷Cs, derived from the atmospheric testing of nuclear weapon testing in the 1950s to 1970s, to estimate rates of soil redistribution on a sloping field with traditional erosion control measures located near Jiajia Village, Jianyang County, in the Sichuan Hilly Basin of China. The local ²¹⁰Pb_ex reference inventory of 12,860 Bq m^− 2 is higher than those reported for many other areas of the world and may reflect the influence of cloudy weather in preventing ²¹⁰Pb released to the atmosphere across the local region moving up into the upper troposphere, where is would be more widely dispersed. The mean ²¹⁰Pb_ex and ¹³⁷Cs inventories measured in cores collected from the upper part of the field with an average slope of 10° were 8028 Bq m^− 2 and 993 Bq m^− 2, respectively, and the equivalent values for the lower part of the field, where the slopes are steeper (20°) were 11,388 Bq m^− 2 and 1299 Bq m^− 2. The pattern of post-fallout ²¹⁰Pb_ex and ¹³⁷Cs redistribution on the sloping field reflects not only the effects of water erosion and redistribution by tillage, but also the local traditional practice of “Tiaoshamiantu”, whereby sediment trapped in the ditches is returned to the fields by the farmer. The estimates of annual rates of soil loss provided by the ²¹⁰Pb_ex measurement are closely comparable with those derived from the ¹³⁷Cs measurements and are consistent with existing knowledge for the study area. The results obtained from this study confirm the potential for using ²¹⁰Pb_ex measurement to estimate soil erosion rates over medium-term timescale of 50–100 years. By combining the estimates of erosion rates provided by the ²¹⁰Pb_ex and ¹³⁷Cs measurements, the weighted mean net soil loss was estimated to be 48.7 t ha^− 1 year^− 1 from the upper subfield and 16.9 t ha^− 1 year^− 1 from the lower subfield. These rates are considerably lower than the erosion rates obtained from runoff plot measurements in the local area. It is suggested that the traditional erosion control practices and the practice of “Tiaoshamiantu” have a significant effect in reducing soil loss and conserving valuable cultivated soil on sloping fields in the Sichuan Hilly Basin.     

Feasibility of using FGD gypsum to conserve water and reduce erosion from an agricultural soil in Georgia

Crop production in Georgia and the Southeastern U.S. can be limited by water. Highly-weathered, drought-prone soils are susceptible to runoff and erosion. Rainfall patterns generate runoff producing storms followed by extended periods of drought during the crop growing season. Thus, supplemental irrigation is often needed to sustain profitable crop production. Increased water retention and soil conservation would efficiently improve water use and reduce irrigation amounts/costs and sedimentation, and sustain productive farm land, thus improving producer's profit margin. Soil amendments, such as flue gas desulfurization (FGD) gypsum, have been shown to retain rainfall and/or irrigation water through increased infiltration while decreasing runoff (R) and sediment (E). Objectives were to quantify rainfall partitioning and sediment delivery improvements with surface applied FGD gypsum from an Ultisol managed to conventional till (CT) and to assess the feasibility of using FGD gypsum on agricultural land in southern Georgia. A field study (Faceville loamy sand, Typic Kandiudult) was established (2006, 2007) near Dawson, GA managed to CT, irrigated cotton (Gossypium hirsutum L.). FGD gypsum application rates evaluated were 0, 1.1, 2.2, 4.5, and 9 Mg ha^− 1. Gypsum treatments and simulated rainfall (50 mm h^− 1 for 1 h) were applied to 2-m wide × 3-m long field plots (n = 3). Runoff and E were measured from each 6-m² plot (slope = 1%). FGD gypsum plots averaged 26% more infiltration (INF), 40% less R, 58% less E, 27% lower maximum R rates (R_max), and 2 times lower maximum E rates (E_max) than control plots. Values of INF and water for crop use increased, and R, E, R_max, and E_max decreased as FGD gypsum application rate increased. Values of INF, R, E, R_max, and E_max for 9 Mg ha^− 1 plots were as much as 17% greater, 35% less, 1.9 times less, 35% less, and 1.9 times less than those from other FGD gypsum plots, respectively; and 40% greater, 40% less, 2.2 times less, 52% less, and 2.9 times less than those from control plots, respectively. Applying FGD gypsum to agricultural lands is a cost-effective management practice for producers in Georgia that beneficially impacts natural resource conservation, producer profit margins, and environmental quality. Agriculture in the Southeast provides a viable market for the electric power industry to convert disposal costs of FGD gypsum into a profitable commodity.     

Natural and anthropogenic controls on soil erosion in the Internal Betic Cordillera (southeast Spain)

Soil erosion in southeast Spain is a complex process due to strong interactions between biophysical and human components. Significant progress has been achieved in the understanding of soil hydrological behavior, despite the fact that most investigations were focused on the experimental plot scale. Although experimental plots allow exploring the effect of multiple biophysical and anthropogenic factors, they provide limited insights in the combined effect of all factors acting together at the landscape scale. In this study, area-specific sediment yields (SSY) have been estimated based on the volume of sediment trapped behind 36 check dams in the southeast of Spain. Low SSY-values were reported (mean = 1.40 t ha⁻¹ year⁻¹: median = 0.61 t ha⁻¹ year⁻¹). SSY variability could be explained for 67% by catchment characteristics such as drainage area, soil characteristics, land cover, average catchment slope, and annual rainfall. The low SSY values are probably caused by the agricultural abandonment that occurred over the past decades and allowed the recovery of natural vegetation. Furthermore, our results suggest that the soils have eroded in the past to such an extent that nowadays not much sediment is detached by overland flow due to residual enrichment of clay and stones. Also, sediment is to a large extent trapped locally in the catchment, as indicated by the negative relationship between SSY and catchment area.     

Establishing a Holocene sediment budget for the river Dijle

A Holocene sediment budget was constructed for the 758 km² Dijle catchment in the Belgian loess belt, in order to understand long-term sediment dynamics. Hillslope sediment redistribution was calculated using soil profile information from 809 soil augerings, which was extrapolated to the entire catchment using morphometric classes. As large parts of the forests within the catchment prove to have undergone little or no erosion since medieval times, a correction was applied for the presence of forests. Total Holocene erosion amounts 817 ± 66 Mt for the catchment, of which 327 ± 34 Mt was deposited as colluvium. This corresponds with a net Holocene soil erosion rate of 10.8 ± 0.8 × 10³ Mg ha^− 1 for the entire Dijle catchment. Alluvial deposits were studied through 187 augerings spread over 17 cross-valley transects. The total alluvial sediment deposition equals 352 ± 11 Mt or 42% of total eroded sediment mass. Results indicate that at the scale of a medium-sized catchment the colluvial sediment sink is as important as the alluvial sediment sink and should not be neglected. As a result the estimation of erosion through alluvial storage and sediment export would yield large errors. Dating of sediment units show an important increase in alluvial deposition from medieval times onwards, indicating the important influence of agricultural activities that developed from that period. Mean sediment export rates from the catchment for the last 1000–1200 years range between 0.8 and 1.3 Mg ha^− 1 a^− 1 and are consistent with present suspended sediment measurements in the Dijle. Erosion for agricultural land for this period is 9.2 ± 2.2 Mg ha^− 1 a^− 1. Sediment budgets for the various tributary catchments provide an insight in the sources and sinks of sediment at different scales within the catchment.     

Animal treading stimulates denitrification in soil under pasture

The effects of animal treading on denitrification in a mixed ryegrass-clover pasture were studied. A single treading event of moderate or severe intensity was applied in plots during spring by using dairy cows at varying stocking rates (4.5 cows 100 m⁻² for 1.5 or 2.5 h, respectively). Treading caused a significant short-term 21 days) increase in denitrification. Denitrification rates reached a maximum of 52 g N₂O-N ha⁻¹ day⁻¹ at 8 days after severe treading compared to 2.3 g N₂O-N ha⁻¹ day⁻¹ under nil treading. Thereafter, denitrification rates declined, and were similar to non-trodden control plots after 28 days. Soil aeration, was significantly reduced by treading as expressed by water-filled porosity. In addition, soil NH₄⁺-N and NO₃⁻-N concentrations were also increased by treading. We propose that the underlying processes involved in increasing denitrification under treading were two-fold. Firstly, treading caused a temporary (e.g. 3 days after treading) reduction in soil aeration through soil physical damage, and secondly, reduced soil N utilisation prompted by reduced plant growth led to increased soil NH₄⁺-N and NO₃⁻-N availability. This study shows that treading, without the influence of other grazing animal factors (e.g. excretion), can cause a large short-term stimulation of denitrification in grass-clover pastures.     

Long-term effects of metal-containing farmyard manure and sewage sludge on soil organic matter in a fluvisol

Our aim was to establish the long-term effects of repeated applications after 20 y of organic amendments (farmyard manure at 10 t ha⁻¹ y⁻¹, and urban sewage sludge at two different rates, 10 t ha⁻¹ y⁻¹ and 100 t ha⁻¹ every 2 y) on the quality of a sandy and poorly buffered soil (Fluvisol, pH 6). Chemical characteristics and biodegradability of the labile organic matter, which is mainly derived from microbial biomass and biodegradation products of organic residues, were chosen as indicators for soil quality. The organic C content had reached a maximal value (30.6 g C kg⁻¹ in the 100 t sludge-treated soil), i.e. about 2.5 times that in the control. Six years after the last application, the organic C content and the microbial biomass content remained higher in sludge-treated soils than in the control. In contrast, the proportion of labile organic matter was significantly lower in sludge-treated soils than in manure-treated and control soils. The labile organic matter of sludge extracts appeared less humified than that of manure-treated and control soils.     

Nitrous oxide emissions from boreal organic soil under different land-use

Nitrous oxide emissions were studied with a static chamber technique during 2 years from a drained organic soil in eastern Finland. After drainage, the soil was forested with birch (Betula pendula Roth) and 22 years later, part of the forest was felled and then used for cultivation of barley (Hordeum vulgare L.) and grass. The annual N₂O emissions from the cultivated soil (from 8.3 to 11.0 kg N₂O-N ha⁻¹ year⁻¹) were ca. twice the annual emission from the adjacent forest site (4.2 kg N₂O-N ha⁻¹ year⁻¹). The N₂O emissions from the soils without plants (kept bare by regular cutting or tilling) were also lower (from 6.5 to 7.1 kg N₂O-N ha⁻¹ year⁻¹) than those from the cultivated soil. There was a high seasonal variation in the fluxes with a maximum in spring and early summer. The N₂O fluxes during the winter period accounted for 15-60% of the total annual emissions. N₂O fluxes during the snow-free periods were related to the water table (WT) level, water-filled pore space, carbon mineralisation and the soil temperature. A linear regression model with CO₂ production, WT and soil temperature at the depth of 5 cm as independent variables explained 54% of the variation in the weekly mean N₂O fluxes during the snow-free periods. N₂O fluxes were associated with in situ net nitrification, which alone explained 58% of the variation in the mean N₂O fluxes during the snow-free period. The N₂O-N emissions were from 1.5 to 5% of net nitrification. The acetylene blockage technique indicated that most of the N₂O emitted in the snow-free period originated from denitrification.     

Effects of gravel on grassland soil carbon and nitrogen in the arid regions of the Tibetan Plateau

Many previous studies have focused on soil gravel concentrations and their effect on crop yields in agricultural systems. The extent of carbon and nitrogen sequestration in soils under steppe systems in relation to surface gravel mulch remains largely unexplored. This study investigated the effects of gravel mulches on soil organic carbon and total nitrogen stocks in the arid and windy regions of the Tibetan Plateau. Surface gravel mulches provide a more favorable environment for soil carbon and nitrogen stocks than do non-mulched sites. Soil organic carbon and total nitrogen stocks were highest (46.9 Mg ha^− 1 SOC and 2.8 Mg ha^− 1 TN) in the medium gravel mulch sites with ~ 40-50% gravel, and lowest (29.5 Mg ha^− 1 SOC and 1.4 Mg ha^− 1 TN) in no gravel mulch sites. Analysis of aggregate size fractions indicated that the vast majority of SOC was present in microaggregate fractions throughout the top 30 cm of soil. Considering the low level of soil disturbance in the study area, the carbon contained in the macroaggregate fraction might become stabilized in the soil. Gravel mulches above the soil surface have an important bearing on soil carbon sequestration as they control wind erosion, decrease soil surface evaporation and change soil physical behavior in the arid and semiarid regions.     

Concentration and stock of carbon in the soils affected by land uses and climates in the western Himalaya,India

Soils are the third biggest sink of carbon on the earth. Hence, suitable land uses for a climatic condition are expected to sequester optimum atmospheric carbon in soils. But, information on how climatic conditions and land uses influence carbon accumulation in the soils on the Himalayan Mountains is not known. This study reports the impact of four climatic conditions (sub-tropical, altitude: 500–1200 m; temperate 1200–2000 m; lower alpine 2000–3000 m; upper alpine, 3000–3500 m) and four land uses (forest, grassland, horticulture, agriculture) on the concentrations and stocks of soil organic carbon (SOC) in upper (0–30 cm) and deeper (30–100 cm) soil depths on the western Himalayan Mountains of India. The study also explored the drivers which influenced the SOC stock build up on the mountains. Rainfall and soil moisture showed quadratic relations, whereas temperature declined linearly with the altitude. SOC stock as well as concentration was the highest (101.8 Mg ha^− 1 in 0–30 cm, 227.97 Mg ha^− 1 in 0–100 cm) in temperate and the lowest in sub-tropical climate (37 Mg ha^− 1 in 0–30 cm, 107.04 Mg ha^− 1 in 0–100 cm). Pattern of SOC stock build up across the altitude was: temperate > lower alpine > upper alpine > sub-tropical. SOC stocks in all land uses across the climatic conditions, except agriculture in lower alpine, was higher (0.7 to 41.6%) in the deeper than upper soil depth. SOC stocks in both the depths showed quadratic relations with soil temperature and soil moisture. Other factors like fine soil particles, land-use factor and altitude influenced positively whereas slope and pH, negatively to the SOC stocks. In all climatic conditions, other than temperate, SOC stocks were greater in natural ecosystems like forests and pastures (112.5 to 247.5 Mg ha^− 1) than agriculture (63 to 120.4 Mg ha^− 1). In temperate climate, SOC stock in agriculture (253.6 Mg ha^− 1) on well formed terraces was a little higher than forest (231.3 Mg ha^− 1) on natural slope. These observations, suggest that land uses on temperate climate may be treated as potential sinks for sequestration of the atmospheric carbon. However, agriculture in subtropical climate need to be pursued with due SOC protection measures like the temperate climate for greater sequestration of the atmospheric carbon.     

Microbial biomass and activity at various soil depths in a Brazilian oxisol after two decades of no-tillage and conventional tillage

The advantages of no-tillage (NT) over conventional tillage (CT) systems in improving soil quality are generally accepted, resulting from benefits in soil physical, chemical and biological properties. However, most evaluations have only considered surface soil layers (maximum 0-30 cm depth), and values have not been corrected to account for changes in soil bulk density. The objective of this study was to estimate a more realistic contribution of the NT to soil fertility, by evaluating C- and N-related soil parameters at the 0-60 cm depth in a 20-year experiment established on an oxisol in southern Brazil, with a soybean (summer)/wheat (winter) crop succession under NT and CT. At full flowering of the soybean crop, soil samples were collected at depths of 0-5, 5-10, 10-20, 20-30, 30-40, 40-50 and 50-60 cm. For the overall 0-60 cm layer, correcting the values for soil bulk density, NT significantly increased the stocks of C (18%) and N (16%) and microbial biomass C (35%) and N (23%) (MB-C and -N) in comparison to CT. Microbial basal respiration and microbial quotient (qMic) were also significantly increased under NT. When compared with CT, NT resulted in gains of 0.8 Mg C ha⁻¹ yr⁻¹ (67% of which was in the 0-30 cm layer) and 70 kg N ha⁻¹ yr⁻¹ (73% in the 0-30 cm layer). In the 0-5-cm layer, MB-C was 82% higher with NT than with CT; in addition, the 0-30 cm layer accumulated 70% of the MB-C with NT, and 58% with CT. In comparison to CT, the NT system resulted in total inputs of microbial C and N estimated at 38 kg C ha⁻¹ yr⁻¹ and 1.5 kg N ha⁻¹ yr⁻¹, respectively. Apparently, N was the key nutrient limiting C and N stocks, and since adoption of NT resulted in a significant increase of N in soils which were deficient in N, efforts should be focused on increasing N inputs on NT systems.     

The impact of organic and inorganic fertilizers and lime on the species-richness and plant functional characteristics of hay meadow communities

Vegetation responses to fertilizers and lime applied in a seven-year study at paired unimproved and semi-improved mesotrophic hay meadows in Cumbria and Monmouthshire, UK, are described in terms of species-richness and several other plant community variables. Treatments were farmyard manure (FYM) applied at rates of between 6 and 24 tonne ha⁻¹ annually or every third year, inorganic fertilizers giving equivalent amounts of N, P and K, and lime applied either alone or with FYM applied annually or three-yearly. Annual FYM at 24 tonne ha⁻¹ reduced species-richness and the richness of positive indicator species at all sites and increased the proportional cover of nutrient-demanding species, whilst liming in conjunction with 12 tonne ha⁻¹ annual FYM application was equally detrimental at the unimproved site in Wales but not in Cumbria. Inorganic fertilizers were apparently no more detrimental to vegetation quality than equivalent FYM treatments, although medium-term nutrient supply from FYM may have been underestimated. Species-richness was maintained by FYM at ?12 tonne ha⁻¹ year⁻¹ in the semi-natural northern meadow, where such levels had been used in the past, but only by amounts equivalent to ?6 tonne ha⁻¹ year⁻¹ at the Welsh sites which had no recent history of fertilizer use. It is unclear to what extent such differences are attributable to innate differences in plant community type, rather than to site-specific differences in past management. The implications of our findings for defining sustainable fertilizer practices to maintain or enhance the nature conservation value of mesotrophic meadows are discussed.     

Responses of soil organic matter and greenhouse gas fluxes to soil management and land use changes in a humid temperate region of southern Europe

We studied the effects of soil management and changes of land use on soils of three adjacent plots of cropland, pasture and oak (Quercus robur) forest. The pasture and the forest were established in part of the cropland, respectively, 20 and 40 yr before the study began. Soil organic matter (SOM) dynamics, water-filled pore space (WFPS), soil temperature, inorganic N and microbial C, as well as fluxes of CO₂, CH₄ and N₂O were measured in the plots over 25 months. The transformation of the cropland to mowed pasture slightly increased the soil organic and microbial C contents, whereas afforestation significantly increased these variables. The cropland and pasture soils showed low CH₄ uptake rates (<1 kg C ha⁻¹ yr⁻¹) and, coinciding with WFPS values >70%, episodes of CH₄ emission, which could be favoured by soil compaction. In the forest site, possibly because of the changes in soil structure and microbial activity, the soil always acted as a sink for CH₄ (4.7 kg C ha⁻¹ yr⁻¹). The N₂O releases at the cropland and pasture sites (2.7 and 4.8 kg N₂O-N ha⁻¹ yr⁻¹) were, respectively, 3 and 6 times higher than at the forest site (0.8 kg N₂O-N ha⁻¹ yr⁻¹). The highest N₂O emissions in the cultivated soils were related to fertilisation and slurry application, and always occurred when the WFPS >60%. These results show that the changes in soil properties as a consequence of the transformation of cropfield to intensive grassland do not imply substantial changes in SOM or in the dynamics of CH₄ and N₂O. On the contrary, afforestation resulted in increases in SOM content and CH₄ uptake, as well as decreases in N₂O emissions.