SOIL ORGANIC CARBON STOCK AND FRACTIONS IN RELATION TO LAND USE AND SOIL DEPTH IN THE DEGRADED SHIWALIKS HILLS OF LOWER HIMALAYAS

The proportional differences in soil organic carbon (SOC) and its fractions under different land uses are of significance for understanding the process of aggregation and soil carbon sequestration mechanisms. A study was conducted in a mixed vegetation cover watershed with forest, grass, cultivated and eroded lands in the degraded Shiwaliks of the lower Himalayas to assess land‐use effects on profile SOC distribution and storage and to quantify the SOC fractions in water‐stable aggregates (WSA) and bulk soils. The soil samples were collected from eroded, cultivated, forest and grassland soils for the analysis of SOC fractions and aggregate stability. The SOC in eroded surface soils was lower than in less disturbed grassland, cultivated and forest soils. The surface and subsurface soils of grassland and forest lands differentially contributed to the total profile carbon stock. The SOC stock in the 1.05‐m soil profile was highest (83.5 Mg ha⁻¹) under forest and lowest (55.6 Mg ha⁻¹) in eroded lands. The SOC stock in the surface (0–15 cm) soil constituted 6.95, 27.6, 27 and 42.4 per cent of the total stock in the 1.05‐m profile of eroded, cultivated, forest and grassland soils, respectively. The forest soils were found to sequester 22.4 Mg ha⁻¹ more SOC than the cultivated soils as measured in the 1.05‐m soil profiles. The differences in aggregate SOC content among the land uses were more conspicuous in bigger water‐stable macro‐aggregates (WSA > 2 mm) than in water‐stable micro‐aggregates (WSA < 0.25 mm). The SOC in micro‐aggregates (WSA < 0.25 mm) was found to be less vulnerable to changes in land use. The hot water soluble and labile carbon fractions were higher in the bulk soils of grasslands than in the individual aggregates, whereas particulate organic carbon was higher in the aggregates than in bulk soils. Copyright © 2012 John Wiley & Sons, Ltd.     

CARBON BUDGET AND SEQUESTRATION POTENTIAL IN A SANDY SOIL TREATED WITH COMPOST

The effects of compost application on soil carbon sequestration potential and carbon budget of a tropical sandy soil was studied. Greenhouse gas emissions from soil surface and agricultural inputs (fertiliser and fossil fuel uses) were evaluated. The origin of soil organic carbon was identified by using stable carbon isotope. The CO₂, CH₄ and N₂O emissions from soil were estimated in hill evergreen forest (NF) plot as reference, and in the corn cultivation plots with compost application rate at 30 Mg ha⁻¹ y⁻¹ (LC), and at 50 Mg ha⁻¹ y⁻¹ (HC). The total C emissions from soil surface were 8·54, 10·14 and 9·86 Mg C ha⁻¹ y⁻¹ for NF, HC and LC soils, respectively. Total N₂O emissions from HC and LC plots (2·56 and 3·47 kg N₂O ha⁻¹ y⁻¹) were significantly higher than from the NF plot (1·47 kg N₂O ha⁻¹ y⁻¹). Total CO₂ emissions from fuel uses of fertiliser, irrigation and machinery were about 10 per cent of total CO₂ emissions. For soil carbon storage, since 1983, it has been increased significantly (12 Mg ha⁻¹) under the application of 50 Mg ha⁻¹ y⁻¹ of compost but not with 30 Mg ha⁻¹ y⁻¹. The net C budget when balancing out carbon inputs and outputs from soil for NF, HC and LC soils were +3·24, −2·50 and +2·07 Mg C ha⁻¹ y⁻¹, respectively. Stable isotope of carbon (δ¹³C value) indicates that most of the increased soil carbon is derived from the compost inputs and/or corn biomass. Copyright © 2011 John Wiley & Sons, Ltd.     

PROJECTED CHANGES IN SOIL ORGANIC CARBON STOCKS UPON ADOPTION OF RECOMMENDED SOIL AND WATER CONSERVATION PRACTICES IN THE UPPER TANA RIVER CATCHMENT,KENYA

Large areas in the Upper Tana river catchment, Kenya, have been over‐exploited, resulting in soil erosion, nutrient depletion and loss of soil organic matter (SOM). This study focuses on sections of the catchment earmarked as being most promising for implementing Green Water Credits, an incentive mechanism to help farmers invest in land and soil management activities that affect all fresh water resources at source. Such management practices can also help restore SOM levels towards their natural level. Opportunities to increase soil organic carbon (SOC) stocks, for two broadly defined land use types (croplands and plantation crops, with moderate input levels), are calculated using a simple empirical model, using three scenarios for the proportion of suitable land that may be treated with these practices (low = 40 per cent, medium = 60 per cent, high = 80 per cent). For the medium scenario, corresponding to implementation on ~348 000 ha in the basin, the eco‐technologically possible SOC gains are estimated at 4·8 to 9·3 × 10⁶ tonnes (Mg) CO₂ over the next 20 years. Assuming a conservative price of US$10 per tonne CO₂‐equivalent on the carbon offset market, this would correspond to ~US$48–93 million over a 20‐year period of sustained green water management. This would imply a projected (potential) payment of some US$7–13 ha⁻¹ to farmers annually; this sum would be in addition to incentives that are being put in place for implementing green water management practices and also in addition to the benefits that farmers would realize from the impact on production of these practices themselves. Copyright © 2012 John Wiley & Sons, Ltd.     

ASSESSMENT OF LAND COVER CHANGES AND THEIR EFFECT ON SOIL ORGANIC CARBON AND SOIL TOTAL NITROGEN IN DAQING PREFECTURE,CHINA

The aim of this study was to examine the influence of land cover changes on soil organic carbon (SOC) and soil total nitrogen (STN) in the Daqing Prefecture of China, where heavy industrialisation in the form of dense oil wells has impacted the environment. Time‐series presentations for the period 1978 to 2008 of remotely sensed data and soil survey data were used to assess the extent of the changes. The study revealed soil degradation under all land cover types and in all soil types, grassland retreat (−15 per cent), swampland retreat (−45 per cent) and increases in the area of farmland (+19 per cent), sand land (+1450 per cent) and alkaline land (+52 per cent). Depletion of the SOC pool occurred in swampland (−64 per cent) both because of the decrease in the area of swampland and because of a decrease in SOC density (−34 per cent). An increase in the SOC pool occurred in alkaline land because of the increase in the area and also because of an increase in SOC density (+297 per cent), but there was little change in the SOC pool in farmland because the increase in area was largely offset by a decrease in SOC density (−14 per cent). The decrease in the STN pool was substantial (−44 per cent), with the largest contributor being the decrease in swamplands (−74 per cent), partly because of the decrease in the area of swampland and partly because of a decrease in STN density (−52 per cent). Large decreases in the STN pool also occurred in farmland (−22 per cent) and grassland (−41 per cent). The direct impacts of construction associated with the expansion of the oil industry were overshadowed by indirect impacts such as interference with water flows and water levels resulting in salinisation of soil. The study also revealed that land cover changes are much more dynamic than a simple analysis would reveal, and because of lag times in the loss of SOC, soil degradation will continue even if land cover changes cease. Copyright © 2012 John Wiley & Sons, Ltd.     

河北曲周盐渍土区的地下水化学特征

对河北曲周县盐渍土区浅层地下水的水化学类型、基本化学性质、主要化学组分及其形式和微量元素的状况及分布等化学特征进行了分析和研究。资料表明，该区地下水化学类型以Cl-SO4型为主，其次为SO4-Cl型。阳离子以Ca∧2 为主，其次为Na∧ 。各地下水化学类型可用于3种特征指标，即rHCO3/r（Cl SO4)、rSO4/rCl和rNa/r（Ca Mg），加以区分。地下水矿化度平均3.11gL∧-1，最高达17gL∧-1。以Cl-SO4和SO4-Cl型的矿化度和离子强度较高。全区纳吸附比较低，基本上无钠害问题。饱和指数表明，地下水中石膏和硬石膏呈非饱和状态，而方解石、霰石呈过饱和状态。除主要游离子外，化学组分形式中CaSO∧04、MgSO∧04、CaHCO∧ 3和MgHCO∧ 3等配合物和配离子的相对浓度较高。地下水中微量元素Cr、Cd和Fe的含量较高，应注意其水质问题，除Zn外，各微量元素浓度均与矿化度呈极显著（或显著）相关。     

喀斯特石漠化过程中土壤氮同位素组成及其空间分异特征

对喀斯特高原区贵州省清镇市王家寨峰丛洼地同一流域内不同类型石漠化、不同等级石漠化以及不同干扰方式石漠化表层土壤全氮的同位素组成及其空间分异特征进行了研究。结果表明：流域内黄壤区样地的表土全氮δ15N值主要分布在＋0.35‰～＋6.82‰之间,平均值为＋4.50‰;黑色石灰土区样地的表土全氮δ15N值主要分布在＋2.70...     

LONG‐TERM MANURING AND FERTILIZER EFFECTS ON DEPLETION OF SOIL ORGANIC CARBON STOCKS UNDER PEARL MILLET‐CLUSTER BEAN‐CASTOR ROTATION IN WESTERN INDIA

Soil organic carbon (SOC) pools are important for maintaining soil productivity and reducing the net CO₂ loading of the atmosphere. An 18‐year old long‐term field experiment involving pearl millet‐cluster bean‐castor sequence was conducted on an Entisol in western India to examine the effects of chemical fertilizers and manuring on carbon pools in relation to crop productivity and C sequestration. The data showed that even the addition of 33.5 Mg ha⁻¹ C inputs through crop residues as well as farm yard manure could not compensate the SOC depletion by oxidation and resulted in the net loss of 4.4 Mg C ha⁻¹ in 18 years. The loss of SOC stock in the control was 12 Mg C ha⁻¹. Conjunctive use of chemical fertilizers along with farm yard manure produced higher agronomic yields and reduced the rate of SOC depletion. The higher average seed yields of pearl millet (809 kg ha⁻¹), cluster bean (576), and castor (827) over six cropping seasons were obtained through integrated use of fertilizers and manure. For every Mg increase in profile SOC stock, there was an overall increase of 0.46 Mg of crop yield, comprising increase in individual yield of pearl millet (0.17 Mg ha⁻¹ y⁻¹ Mg⁻¹ SOC), cluster bean (0.14) and castor (0.15). The magnitude of SOC build up was proportional to the C inputs. Carbon pools were significantly correlated with SOC, which increased with application of organic amendments. Threshold C input of 3.3 Mg C ha⁻¹ y⁻¹ was needed to maintain the SOC stock even at the low antecedent level. Copyright © 2011 John Wiley & Sons, Ltd.     

稻草还田配施化肥与腐秆菌剂下的土壤微生物及有机碳组分特征

通过田间试验,研究了稻草还田配施化肥与腐秆菌剂对早稻土壤微生物、酶活性及有机碳组分和产量的影响。结果表明:稻草还田配施化肥与菌剂可以有效地提高土壤细菌、真菌、放线菌数量,增强蔗糖酶、脲酶、过氧化氢酶的活性。与稻草不还田施肥(F)和不施肥(CK)相比,稻草还田配施化肥与菌剂(SFM),提高了土壤不同形态有机碳含量和碳库管理指数,其中活性有机碳、碳库管理指数分别提高了10.33%～28.88%、12.85%～30%;并且因为有利于早稻分蘖,产量增加3.56%～23.29%。可见,稻草还田配施化肥与菌剂,不仅可以提高产量,而且对改善稻田土壤肥力也有重要的作用。