Foraging pits of the short-beaked echidna (Tachyglossus aculeatus) as small-scale patches in a semi-arid Australian box woodland

Many animals create disturbances on the soil surface while constructing habitat and resting sites, or foraging for food. This soil disturbance, which is sometimes known as biopedturbation, is a major contributor to landscape patchiness in arid and semi-arid environments. In the semi-arid woodlands of eastern Australia, the Short-Beaked Echidna (Tachyglossus aculeatus) creates a mosaic of foraging pits close to the canopies of large trees. The effects of pits on physical, chemical and biological properties of soils were compared at seven sites, each with two levels of disturbance (foraging pit vs. surface) and two canopy locations (under the canopy, in the open) associated with two tree species (Eucalyptus intertexta, Alectryon oleifolius). Foraging pits trapped twice the mass of litter compared with adjacent non-pit surfaces, and there was more litter under the tree canopies than in the open. Pits contained more bark and leaf material, and larger pits tended to trap more litter. Soil electrical conductivity levels were lower in the pits, and although there were greater concentrations of soil nutrients under the canopy, the concentrations of total carbon, nitrogen and sulphur were lower in the pits compared with the surface. Changes in litter mass did not explain differences in soil carbon, nitrogen or phosphorus. Soil in the pit was moister and more porous, and surface temperatures below the litter in the pits about 2 °C lower than at the surface. Respiration was about 30% greater in the pits, and both the early (sorptivity) and late (steady-state infiltration) stages of infiltration were significantly greater in the pits. Soil micro-arthropods were more abundant in the pits, which supported a different complement of taxa, but a similar diversity, to non-pit surfaces. Our results indicate that echidna foraging pits act as substantial resource traps. Given their extensive distribution in semi-arid woodlands, and their marked influence on soil biogeochemistry, echidnas should be seen as important ecosystem engineers in woodland critical for the maintenance of small-scale patchiness and, therefore, the efficient functioning of arid and semi-arid ecosystems.     

南方红壤丘陵区水土流失现状与综合治理对策

  目的  探究红壤丘陵区不同林分林下土壤颗粒粒级分布特征和土壤养分含量,为该地区林分升级、土壤肥力改善和纯林可持续经营提供理论依据。  方法  以红壤丘陵区3种典型林分林下土壤作为研究对象,运用相关性分析和逐步回归分析探讨不同林分类型土壤颗粒粒级分布特征、分形维数及其与土壤养分含量的相互关系。  结果  ① 3种林分土壤质地类型主要集中在粉壤土、粉土和砂壤土,3种林分分形维数的大小为：桉树 × 红锥混交林 > 桉树纯林 > 红锥纯林。② 除土壤全磷以外,不同林分类型和土层均对土壤养分含量具有显著性影响（P < 0.05）,尤其混交林中更为明显。但两者之间的交互作用仅对有机质、全氮和全钾具有显著性影响（P < 0.05）,而对pH和全磷无显著影响。③ 土壤颗粒分形维数与黏粒含量呈极显著正相关,与土壤粉粒、有机质和全氮的含量呈显著负相关性（P < 0.05）,同时土壤颗粒分形维数与黏粒、粉粒、极细砂、全氮和全钾呈极显著线性相关性（P < 0.001）。  结论  土壤颗粒的分形特征可以在一定程度上反映不同林分类型土壤颗粒粒级分布特征及其养分含量,而混交林较纯林土壤分形维数和养分含量均高于纯林,混交林较纯林具有更优越的保水保土功能和更高的土壤肥力水平。     

Changes of soil organic carbon and its fractions in relation to soil physical properties in a long-term fertilized paddy

Soil organic carbon (SOC) has an important role in improving soil quality and sustainable production. A long-term fertilization study was conducted to investigate changes in SOC and its relation to soil physical properties in a rice paddy soil. The paddy soils analyzed were subjected to different fertilization practices: continuous application of inorganic fertilizers (NPK, N–P–K = 120–34.9–66.7 kg ha⁻¹ yr⁻¹ during 1967–1972 and 150–43.7–83.3 kg ha⁻¹ yr⁻¹ from 1973 to 2007), straw based compost (Compost, 10 Mg ha⁻¹ yr⁻¹), a combination of NPK + Compost, and no fertilization (control). Soil physical properties were investigated at rice harvesting stage in the 41st year for analyzing the relationship with SOC fraction. Continuous compost application increased the total SOC concentration in plough layers and improved soil physical properties. In contrast, inorganic or no fertilization markedly decreased SOC concentration resulting to a deterioration of soil physical health. Most of the SOC was the organo-mineral fraction (<0.053 mm size), accounting for over 70% of total SOC. Macro-aggregate SOC fraction (2–0.25 mm size), which is used as an indicator of soil quality rather than total SOC, covered 8–17% of total SOC. These two SOC fractions accumulated with the same tendency as the total SOC changes. Comparatively, micro-aggregate SOC (0.25–0.053 mm size), which has high correlation with physical properties, significantly decreased with time, irrespective of the inorganic fertilizers or compost application, but the mechanism of decrease is not clear. Conclusively, compost increased total SOC content and effective SOC fraction, thereby improving soil physical properties and sustaining production.     

套种绿肥对茶园土壤理化性状的影响

通过田间小区试验,以不套种任何绿肥处理为对照,研究了白三叶(Trifolium repens L.)、多年生黑麦草(Lolium perenne L.)和两者混播的3种套种模式对茶园土壤理化性状及环境小气候的影响。结果表明:茶园套种绿肥有降低土壤体积质量、降低土壤紧实度、改善土壤气相和液相比例的趋势,套种绿肥可明显降低地表、5 cm、10 cm和15 cm土层温度,减小土壤温度变幅。最高温时,各土层降温效果均为:黑麦草白三叶混播。绿肥处理的土壤有机质含量、全氮含量、速效磷含量和速效钾含量较对照有所增加,增幅分别为6.67%~12.6%、0.8%~15.2%、24.1%~26.7%和6.8%~88.9%。绿肥处理与对照相比,土壤微生物数量明显增加:细菌数量、真菌数量、放线菌数量分别是对照的1.75倍~2.58倍、1.22倍~1.88倍和1.15倍~1.46倍。因此,茶园套种白三叶和套种黑麦草对土壤生态环境效应的改善和茶园土壤基本肥力的效果相对更佳,值得在生产上进一步推广应用。     

Seasonal differences in tillage draught on a sandy loam soil with long‐term additions of animal manure and mineral fertilizers

Energy requirements for soil tillage are closely linked to soil properties, such as clay, water and soil organic carbon (SOC) contents. Long‐term application of inorganic fertilizer and organic amendments affects SOC content but little is known about seasonal differences in tillage draught requirements of soils subject to contrasting nutrient management regimes. We assessed autumn and spring tillage draught following harvest of early‐sown and timely sown winter wheat grown on a sandy loam in the Askov Long‐Term Experiment on Animal Manure and Mineral Fertilizers. Draught force was related to soil texture, soil water and SOC content, shear strength and bulk density, nutrient management, and yield of the preceding winter wheat. Contents of clay and SOC ranged from 8.9 to 10.6% and from 0.98 to 1.36%, respectively. In the autumn and spring, SOC normalized by clay content explained 38 and 5% of the variation in specific draught, respectively. Specific draught did not differ significantly among individual fertilization treatments. SOC was closely correlated with clay and water contents and bulk density, and with yield of the preceding wheat. Draught force was significantly smaller in the spring than in the autumn. In the autumn when soils were drier (?700 hPa), tillage draught was correlated with several soil characteristics, whereas water content was the dominating parameter in the spring when soils were wetter (?100 hPa). The range of SOC contents observed in this study aligns with that observed in Danish sandy loams under intensive cultivation, and within this range, SOC per se had little effect on draught requirements.     

Humus forms in terrestrial ecosystems: a framework to biodiversity

Humus forms are the seat of most biological transformations taking place in terrestrial ecosystems, being at the interface between plants, animals and microbes. The diversity of terrestrial humus forms (mor, moder and mull) can be attributed to the existence of different patterns (strategies) for the capture and use of resources by ecosystems, in ascending order of biodiversity and bioavailability. Arguments are found in the parallel development of humus forms and terrestrial ecosystems, in exclusion mechanisms between organisms living in different humus forms, and in palaeontological studies. The diversification of terrestrial life forms in the course of Earth history, concomitant with an improvement in resource availability due to the development of sedimentary layers at the surface of continents, may explain the successive appearance of more active humus forms enabling the co-existence of an increasing number of organisms. Contradictory reports about the relationships between biodiversity and stability of ecosystems can be explained by the existence of different belowground pathways making ecosystems more stable.     

Spatial and Fractal Characterization of Soil Chemical Properties and Nutrients across Depths in a Clay-Loam Soil

Researchers assessed the spatial distribution of soil chemical properties and nutrients at four depths in a clay loam soil cropped to corn and soybean at Freeman farm of Lincoln University. Soil samples were taken at depths of 0–10, 10–20, 20–40, and 40–60 cm in a 4.05-ha field and analyzed for acidity or basicity (pH), cation exchange capacity (CEC), total carbon (TC), organic matter (OM), base saturations on the CEC, ammonium (NH₄⁺), nitrate (NO₃^?), phosphorus (P), potassium (K), calcium (Ca), sulfur (S), magnesium (Mg), sodium (Na), manganese (Mn), copper (Cu), iron (Fe), and zinc (Zn). Results showed that coefficients of variation (CV) ranged between 5 and 30%, except for TC, NO₃^?, and Zn, which had greater CVs. Soil chemical properties and nutrients responded to exponential, linear, Gaussian, and spherical variogram models with nugget-to-sill ratios ≤ 1.0 and effective ranges from 4 to 56 m. Fractal analysis showed that CEC in all depths belonged to the 1.99 ≥ D3 ≥ 1.90 group, which suggests great disorder and antipersistence in the spatial structure.     

Amelioration of a highly alkaline soil by trees in northern India

Abstract. A study was carried out to compare the impact of 6-year-old plantations of Prosopis juliflora (Swartz) D.C., Dalbergia sissoo Roxb. Ex. D.C. and Eucalyptus tereticornis Sm. on the physical and chemical properties of sodic soil in the Indo-Gangetic alluvial plains of Uttar Pradesh, India. Soil properties under the three tree species showed significant improvement through a reduction in the pH, electrical conductivity, exchangeable sodium percentage, CaCO₃ and gypsum requirement, and by increase in organic C, total N, and available P and K. The six years of reclamation had achieved a marked reduction in exchangeable sodium (from 11.5 to 4.5 cmol_c kg⁻¹) to a depth of 1.5 m in the soil profile, whereas the levels of exchangeable calcium, magnesium and potassium had increased. There was also a significant reduction in soil bulk density (from 1.66 to 1.24 g cm⁻³) and increases in porosity, water holding capacity, field capacity, permeability and infiltration rate. The equilibrium infiltration rate after 455 min increased from 0.03 cm h⁻¹ in the control to 0.13 cm h⁻¹ under P juliflora and D. sissoo and 0.10 cm h⁻¹ under E. tereticornis . It is concluded that salt-tolerant tree species have a significant impact on soil properties, which could help to rehabilitate the sodic wastelands in the region.     

Biochemical properties in managed grassland soils in a temperate humid zone: modifications of soil quality as a consequence of intensive grassland use

Although soil biochemical properties are considered to be good indicators of changes in soil quality, few studies have been made of the changes in biochemical properties brought about by anthropogenic disturbance of grassland ecosystems. In the present study, several biochemical properties were analysed in 31 grassland soils subjected to a high level of management, and the values obtained were compared with known values corresponding to native grasslands from the same region (Galicia, NW Spain). The 31 managed grasslands were divided into two groups (re-sown grasslands and improved grasslands) according to their management and past land use. The biochemical properties studied were: labile carbon, microbial biomass carbon, microbial respiration, metabolic quotient, net nitrogen mineralisation and the activities of dehydrogenase, catalase, phosphodiesterase, phosphomonoesterase, casein hydrolysing proteases, benzoyl arginamide (BAA)-hydrolysing proteases, urease, cellulase, ß-glucosidase, invertase and arylsulphatase. Managed grasslands exhibited lower values of soil biochemical properties than native grasslands. Three biochemical equilibrium equations were used to compare soil quality in managed and native grasslands. One of the equations did not show any significant difference between the groups of grassland soils considered. In contrast, two of the equations showed similar soil quality for improved and native grasslands, while re-sown grasslands exhibited a loss of soil quality when compared to native grassland soils.     

Grassland conversion along a climate gradient in northwest China: Implications for soil carbon and nutrients

Soil organic carbon (SOC) stocks and nutrient availability are key indicators of soil quality, and both can be influenced by land-use change. However, it is still unclear whether the impact of land-use change on SOC and nutrient stocks differs between ecoregions. Grasslands near the northeast border of the Qinghai-Tibetan Plateau (QTP) occur across several ecoregions that have recently been subjected to substantial land-use change. Based on long-term land-use history, we conducted a field investigation comparing soil C and nutrient stocks between natural grassland (NGL) and three types of converted grassland (agricultural grassland, AGL; farmland, FL; and abandoned farmland, AFL) in three ecoregions along a climate gradient: alpine meadow, temperate steppe and temperate desert. Compared with NGL, soil C stocks in converted grasslands were 22%–30% lower in the alpine meadow, but 60–82% higher in the temperate steppe and 6%–76% higher in the temperate desert. Converted grasslands also contained higher stocks of available nitrogen and phosphorus than NGL in the temperate steppe and desert. Soils (0–40 cm) in NGL contained 14.8 ± 0.1 kg C m⁻² in alpine meadow, 6.7 ± 0.6 kg C m⁻² in temperate steppe and 1.7 ± 0.3 kg C m⁻² in temperate desert. Together, our results indicate that the responses of soil C and nutrients to grassland conversion differed between ecoregions. Thus, to optimize soil C sequestration rates and overall soil quality, we suggest that land-use policies in this area should take into account local environmental conditions.     

Biotic interactions in Antarctic terrestrial ecosystems: Are they a factor?

Antarctic terrestrial ecosystems are noted for their relative simplicity and limited trophic structure. In this context, knowledge of biotic interactions in structuring terrestrial soil communities would seem beneficial from a theoretical perspective as well as from a conservation perspective. Unfortunately, although biotic interactions are generally seen as being insignificant in these unique ecosystems, this view is based upon few explicit studies and very little is known of the role that biotic interactions may play. Accordingly, we review our current understanding of these interactions, including analogues from other appropriate ecosystems. On the basis of this review, we conclude that: (1) Antarctic terrestrial systems are predominantly abiotically-driven systems; and (2) a network of manipulative field and laboratory experiments are needed for establishing any role for biotic interactions in structuring Antarctic soil environments.     

Chemical and microbial properties in a greenhouse loamy soil after steam disinfestation alone or combined with CaO addition

Steam disinfestation represents an increasingly attractive strategy to control soil-borne pathogens and weeds both in greenhouses and field crops. Beyond pest control, steam injection has the potential to alter soil nutrient dynamics and composition of bacterial communities. This study investigated the impact of a soil-steaming method (the Bioflash™ system) on main chemical (total organic C, TOC; total N, TN; cation exchange capacity, CEC; exchangeable Na, K, Mg and Ca; KCl-extractable ammonium and nitrate, DTPA-exchangeable Mn) and microbial (microbial biomass C, MBC; genetic structure of bacterial communities) properties in a greenhouse loamy soil. Treatments were carried out by using a self-propelled soil-steaming machine operating at two steaming modes (deep or shallow) in combination or not with addition of an exothermically reacting compound (CaO at a 1000 kg ha⁻¹ rate). Soils from a five-treatment (NS, non-steamed soil, DS, deep steam injection; DS + E, deep steam injection plus CaO; SS, shallow steam injection; SS + E, shallow steam injection plus CaO) plot block were sampled before steaming and after 8, 19, 54 and 91 days. Compositional shifts in the structure of soil bacterial communities were monitored by denaturing gradient gel electrophoresis (DGGE) fingerprinting of soil-extracted 16S rRNA gene fragments, using primers specific for Bacteria and Actinobacteria. Maximum soil temperature reached 70 °C (DS) and 82 °C (DS + E) in the 10-20 cm layer; and 50 °C (SS) and 53 °C (SS + E) in the 0-10 cm layer. TOC, TN, CEC, exchangeable Na, Mg and Ca were not statistically affected by soil steaming, CaO addition, depth of injection or their interactions. Conversely, SS promoted a large release of exchangeable K, notwithstanding CaO addition. Steam disinfestation significantly stimulated ammonium release, which further increased in CaO-treated steamed soils. Generally ammonium and nitrate pools varied oppositely, being the latter markedly reduced at the end of the observation period. Available Mn was significantly increased by soil steaming, but it was depressed when steaming was combined with CaO addition. Soil steaming markedly reduced the MBC, especially in DS-treated and SS-treated plots. The genetic structure of soil bacterial and actinobacterial communities was largely unresponsive to the steaming treatments. Even though the Bioflash™ system did not cause bacterial eradication or compositional shifts in bacterial community structure, soil steaming stimulated an increased release of soluble nutrients (K⁺, Mn²⁺, NH₄⁺-N). Over a longer perspective, excessive soil resources exploitation and potential risks of Mn toxicity should be cautiously considered especially in repeatedly (and eventually acid) steamed soils.     

Ecological conditions for Saxifraga hirculus in Central Europe: A better understanding for a good protection

Saxifraga hirculus is a postglacial relict in Central Europe, whose populations suffered a dramatic decrease in the 19th and 20th centuries. However, few researchers have been interested in its ecological requirements in Central Europe. This article synthesizes previous knowledge supplemented by original data from the last large population (Switzerland).S. hirculus is a weak competitor which needs precise ecological conditions. It grows on bryophyte carpets in neutral to slightly acid wetlands, with stable water table close to the soil surface (optimum between 8 and 14 cm) but does not stand long flooding. However, it requires a good oxygen supply, with roots 2-3 cm under the soil surface, generally not reached by water, with running, cold water through loose, fibric peat. Its optimal conditions are in spring fens, but it grows in other types of wetlands as well. However, overgrowing by shrubs, sedges or Sphagnum in natural successions may threaten the species with extinction, as did drainage and peat extraction previously. Now, its survival in Central Europe depends on an adequate management of the ecosystems. Moderate grazing (cattle or sheep) or mowing help to limit competition with taller Carex species. Reintroduction of disappeared populations or creation of new ones from cultivation in botanical garden is possible, but appropriate sites are rare. In some cases, substrate management could improve the conditions in somewhat inadequate situations. This management in four directions can be flexibly applied in different situations to progress to optimal conditions for the conservation of this valuable species.     

Late Quaternary eolian dust in surficial deposits of a Colorado Plateau grassland: Controls on distribution and ecologic effects

In a semi-arid, upland setting on the Colorado Plateau that is underlain by nutrient-poor Paleozoic eolian sandstone, alternating episodes of dune activity and soil formation during the late Pleistocene and Holocene have produced dominantly sandy deposits that support grass and shrub communities. These deposits also contain eolian dust, especially in paleosols. Eolian dust in these deposits is indicated by several mineralogic and chemical disparities with local bedrock, but it is most readily shown by the abundance of titaniferous magnetite in the sandy deposits that is absent in local bedrock. Magnetite and some potential plant nutrients (especially, P, K, Na, Mn, and Zn) covary positively with depth (3–4 m) in dune-crest and dune-swale settings. Magnetite abundance also correlates strongly and positively with abundances of other elements (e.g., Ti, Li, As, Th, La, and Sc) that are geochemically stable in these environments. Soil-property variations with depth can be ascribed to three primary factors: (1) shifts in local geomorphic setting; (2) accumulation of relatively high amounts of atmospheric mineral dust inputs during periods of land-surface stability; and (3) variations in dust flux and composition that are likely related to changes in dust-source regions. Shifts in geomorphic setting are revealed by large variations in soil texture and are also expressed by changes in soil chemical and magnetic properties. Variable dust inputs are indicated by both changes in dust flux and changes in relations among magnetic, chemical, and textural properties. The largest of these changes is found in sediment that spans late Pleistocene to early Holocene time. Increased dust inputs to the central Colorado Plateau during this period may have been related to desiccation and shrinkage of large lakes from about 12 to 8 ka in western North America that exposed vast surfaces capable of emitting dust. Soil properties that result from variable dust accumulation and redistribution in these surficial deposits during the late Quaternary are important to modern ecosystem dynamics because some plants today utilize nutrients deposited as long ago as about 12–15 ky and because variations in fine-grained (silt) sediment, including eolian dust, influence soil-moisture capacity.     

Soil losses due to potato harvesting: a case study in western Turkey

Harvesting of potato (Solanum tuberosum L.) may cause soil losses, but the magnitude of such losses has not been widely documented. We quantified the amount of soil lost with the mechanical harvesting of potatoes in 39 fields in western Turkey in 2013. The amount of soil lost was 1.81 Mg/ha/harvest and increased with increased gravimetric water content and plant density. The cost to replace nutrients lost with soil was about US$3 per hectare. Overall, soil loss due to potato harvesting is an important component of total erosion in the study region.     

The elusive role of soil quality in nutrient cycling: a review

Cycling of nutrients, including nitrogen and phosphorus, is one of the ecosystem services we expect agricultural soils to deliver. Nutrient cycling incorporates the reuse of agricultural, industrial and municipal organic residues that, misleadingly, are often referred to as ‘wastes’. The present review disentangles the processes underlying the cycling of nutrients to better understand which soil properties determine the performance of that function. Four processes are identified (i) the capacity to receive nutrients, (ii) the capacity to make and keep nutrients available to crops, (iii) the capacity to support the uptake of nutrients by crops and (iv) the capacity to support their successful removal in harvested crop. Soil properties matter but it is imperative that, as constituents of ‘soil quality’, they should be evaluated in the context of management options and climate and not as ends in their own right. The effect of a soil property may vary depending on the prevailing climatic and hydrologic conditions and on other soil properties. We recognize that individual soil properties may be enhancing one of the processes underlying the cycling of nutrients but simultaneously weakening others. Competing demands on soil properties are even more obvious when considering other soil functions such as primary production, purification and flow regulation of water, climate modification and habitat provision, as shown by examples. Consequently, evaluations of soil properties and management actions need to be site‐specific, taking account of local aspects of their suitability and potential challenges.     

Changes in the carbon concentrations and other soil properties of some Scottish agricultural soils: Evidence from a resampling campaign

The change in soil carbon (C) concentration, soil pH and major nutrients for approximately 1,000 topsoil sampled from on-farm experimental sites over a thirty-year period from 1950 to 1980 in north-east Scotland are summarized. This period coincided with increased agricultural intensification, which included regular liming and fertilizer additions. During 2017, 37 of these sites were resampled and reanlaysed. While pH and extractable phosphorus (P) and potassium (K) increased over this period, there was no detectable change in the percentage loss on ignition. Composite soil samples were taken by auger from a depth of 0–15 cm and compared with the corresponding archived samples collected at the initiation of each experiment. Analysis of these resampled soils indicated no significant change in soil carbon (C), although soil pH, extractable magnesium (Mg) and K and Nitrogen (N) concentrations were significantly greater (p < .001) but extractable soil P concentration was significantly less (p = .015) compared with the original samples. Even though measuring C concentration alone is a poor indicator of overall changes in soil C stocks, it does provide a relative quick “early warning” of C losses that would justify a more comprehensive measure of stocks.     

Assessing soil properties and nutrient availability under conservation agriculture practices in a reclaimed sodic soil in cereal-based systems of North-West India

Soil quality degradation associated with resources scarcity is the major concern for the sustainability of conventional rice-wheat system in South Asia. Replacement of conventional management practices with conservation agriculture (CA) is required to improve soil quality. A field experiment was conducted to assess the effect of CA on soil physical (bulk density, penetration resistance, infiltration) and chemical (N, P, K, S, micronutrients) properties after 4 years in North-West India. There were four scenarios (Sc) namely conventional rice-wheat cropping system (Sc1); partial CA-based rice-wheat-mungbean system (RWMS) (Sc2); CA-based RWMS (Sc3); and CA-based maize-wheat-mungbean (Sc4) system. Sc2 (1.52 Mg m^?3) showed significantly lower soil bulk density (BD). In Sc3 and Sc4, soil penetration resistance (SPR) was reduced and infiltration was improved compared to Sc1. Soil organic C was significantly higher in Sc4 than Sc1. Available N was 33% and 68% higher at 0–15 cm depth in Sc3 and Sc4, respectively, than Sc1. DTPA extractable Zn and Mn were significantly higher under Sc3 and Sc4 compared to Sc1. Omission study showed 30% saving in N and 50% in K in wheat after four years. Therefore, CA improved soil properties and nutrient availability and have potential to reduce external fertilizer inputs in long run.     

Regulation of nitrogen mineralization and nitrification in Southern Appalachian ecosystems: Separating the relative importance of biotic vs. abiotic controls

Long-term measurements of soil nitrogen (N) transformations along an environmental gradient within the Coweeta Hydrologic Laboratory basin in western North Carolina showed a strong seasonal pattern and suggested that vegetation community type—through its influence on soil properties—was an important regulating factor. Our objective was to determine the relative effects of biotic vs. abiotic factors on soil N transformations. During the 1999 and 2000 growing seasons we transplanted soil cores from each of the five gradient plots to all other gradient plots for their 28-day in situ incubation. N mineralization and nitrification rates in soils from the northern hardwood (NH) site were significantly increased when soils were transplanted to warmer sites. N mineralization rates also increased in transplanted soil from the dry mixed-oak/pine site to a wetter site. Multiple regression analysis of N mineralization from all five sites found that biotic (total soil N and C:N ratios) and climatic factors (moisture and temperature) regulate N mineralization. Regression analyses of individual sites showed that N mineralization rates responded to variation in temperature and moisture at only the high elevation northern hardwood site and moisture alone on the dry warm mixed-oak/pine site. N mineralization was unrelated to temperature or moisture at any of the other sites. Results indicate that soil properties plus climatic conditions affect soil N transformations along the environmental gradient at Coweeta. Environmental controls were significant only at the extreme sites; i.e., at the wettest and warmest sites and soils with highest and lowest C and N contents. The high degree of temperature sensitivity for the northern hardwood soils indicates potentially large responses to climatic change at these sites.     

Farmland degradation in the mountains of Nepal: a study of watersheds ‘with’ and ‘without’ external intervention

Amidst growing concerns about farmlands conservation, this paper examines the status of farmlands in two mountain watersheds ‘with’ and ‘without’ external intervention, located in the western hills of Nepal. Information was obtained from a household survey and group discussions conducted during April to September 1999. The severity of soil erosion from farmers' perspectives, density of landslides, soil nutrient balance and change in crop yield have been adopted as indicators of the status of the land. Results of the analysis indicate that land resources in both watersheds are undergoing degradation, though the causes and extent of degradation vary from one type of land to another. Upland crop terraces, locally called bari, are undergoing degradation most seriously under the combined influence of severe soil erosion, landslide and the depletion of soil nutrients. In particular, soil erosion has severely affected nearly half of the upland crop terraces in both watersheds due to a number of natural and anthropogenic factors ranging from weak geological structure to arable agriculture. Landslide and nutrient depletion have affected all types of farmlands except homesteads in both watersheds. Overall, the extent and intensity of land degradation is relatively high in the non‐project area, as farmers were not provided with necessary technical and financial support. A broad strategy has been outlined for effective conservation of farmlands. Copyright © 2002 John Wiley & Sons, Ltd.